path: root/doc/guix.de.texi

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@c %**start of header
@setfilename guix.de.info
@documentencoding UTF-8
@documentlanguage de
@frenchspacing on
@settitle Referenzhandbuch zu GNU Guix
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@include version-de.texi

@c Identifier of the OpenPGP key used to sign tarballs and such.
@set OPENPGP-SIGNING-KEY-ID 3CE464558A84FDC69DB40CFB090B11993D9AEBB5

@copying
Copyright @copyright{} 2012, 2013, 2014, 2015, 2016, 2017, 2018 Ludovic
Courtès@* Copyright @copyright{} 2013, 2014, 2016 Andreas Enge@* Copyright
@copyright{} 2013 Nikita Karetnikov@* Copyright @copyright{} 2014, 2015,
2016 Alex Kost@* Copyright @copyright{} 2015, 2016 Mathieu Lirzin@*
Copyright @copyright{} 2014 Pierre-Antoine Rault@* Copyright @copyright{}
2015 Taylan Ulrich Bayırlı/Kammer@* Copyright @copyright{} 2015, 2016, 2017
Leo Famulari@* Copyright @copyright{} 2015, 2016, 2017, 2018 Ricardo
Wurmus@* Copyright @copyright{} 2016 Ben Woodcroft@* Copyright @copyright{}
2016, 2017, 2018 Chris Marusich@* Copyright @copyright{} 2016, 2017, 2018
Efraim Flashner@* Copyright @copyright{} 2016 John Darrington@* Copyright
@copyright{} 2016, 2017 Nils Gillmann@* Copyright @copyright{} 2016, 2017,
2018 Jan Nieuwenhuizen@* Copyright @copyright{} 2016 Julien Lepiller@*
Copyright @copyright{} 2016 Alex ter Weele@* Copyright @copyright{} 2017,
2018 Clément Lassieur@* Copyright @copyright{} 2017 Mathieu Othacehe@*
Copyright @copyright{} 2017 Federico Beffa@* Copyright @copyright{} 2017,
2018 Carlo Zancanaro@* Copyright @copyright{} 2017 Thomas Danckaert@*
Copyright @copyright{} 2017 humanitiesNerd@* Copyright @copyright{} 2017
Christopher Allan Webber@* Copyright @copyright{} 2017, 2018 Marius Bakke@*
Copyright @copyright{} 2017 Hartmut Goebel@* Copyright @copyright{} 2017
Maxim Cournoyer@* Copyright @copyright{} 2017, 2018 Tobias Geerinckx-Rice@*
Copyright @copyright{} 2017 George Clemmer@* Copyright @copyright{} 2017
Andy Wingo@* Copyright @copyright{} 2017, 2018 Arun Isaac@* Copyright
@copyright{} 2017 nee@* Copyright @copyright{} 2018 Rutger Helling@*
Copyright @copyright{} 2018 Oleg Pykhalov@* Copyright @copyright{} 2018 Mike
Gerwitz@* Copyright @copyright{} 2018 Pierre-Antoine Rouby@* Copyright
@copyright{} 2018 Gábor Boskovits@* Copyright @copyright{} 2018 Florian
Pelz@*

Es ist Ihnen gestattet, dieses Dokument zu vervielfältigen, weiterzugeben
und/oder zu verändern, unter den Bedingungen der GNU Free Documentation
License, entweder gemäß Version 1.3 der Lizenz oder (nach Ihrer Option)
einer späteren Version, die von der Free Software Foundation veröffentlicht
wurde, ohne unveränderliche Abschnitte, ohne vorderen Umschlagtext und ohne
hinteren Umschlagtext. Eine Kopie der Lizenz finden Sie im Abschnitt mit dem
Titel »GNU Free Documentation License«.
@end copying

@dircategory Systemadministration
@direntry
* Guix: (guix.de).           Installierte Software und Systemkonfigurationen 
                               verwalten.
* guix package: (guix.de)guix package aufrufen.  Pakete installieren, 
                                                   entfernen und 
                                                   aktualisieren.
* guix gc: (guix.de)guix gc aufrufen.  Unbenutzten Plattenspeicher wieder 
                                         freigeben.
* guix pull: (guix.de)guix pull aufrufen.  Die Liste verfügbarer Pakete 
                                             aktualisieren.
* guix system: (guix.de)guix system aufrufen.  Die 
                                                 Betriebssystemkonfiguration 
                                                 verwalten.
@end direntry

@dircategory Softwareentwicklung
@direntry
* guix environment: (guix.de)guix environment aufrufen.  Umgebungen für 
                                                           Entwickler 
                                                           erstellen
* guix build: (guix.de)guix build aufrufen.  Erstellen von Paketen.
* guix pack: (guix.de)guix pack aufrufen.  Bündel aus Binärdateien 
                                             erstellen.
@end direntry

@titlepage
@title Referenzhandbuch zu GNU Guix
@subtitle Den funktionalen Paketmanager GNU Guix benutzen
@author Die GNU-Guix-Entwickler

@page
@vskip 0pt plus 1filll
Edition @value{EDITION} @* @value{UPDATED} @*

@insertcopying
@end titlepage

@contents

@c *********************************************************************
@node Top
@top GNU Guix

Dieses Dokument beschreibt GNU Guix, Version @value{VERSION}, ein
funktionales Paketverwaltungswerkzeug, das für das GNU-System geschrieben
wurde.

@c TRANSLATORS: You can replace the following paragraph with information on
@c how to join your own translation team and how to report issues with the
@c translation.
This manual is also available in French (@pxref{Top,,, guix.fr, Manuel de
référence de GNU Guix}).  If you would like to translate it in your native
language, consider joining the
@uref{https://translationproject.org/domain/guix-manual.html, Translation
Project}.

@menu
* Einführung::              Was ist Guix überhaupt?
* Installation::             Guix installieren.
* Paketverwaltung::          Pakete installieren, aktualisieren usw.
* Programmierschnittstelle::  Guix in Scheme verwenden.
* Zubehör::                 Befehle zur Paketverwaltung.
* GNU-Distribution::         Software für Ihr freundliches GNU-System.
* Mitwirken::                Ihre Hilfe ist nötig!

* Danksagungen::             Danke!
* GNU-Lizenz für freie Dokumentation::  Die Lizenz dieses Handbuchs.
* Konzeptverzeichnis::       Konzepte.
* Programmierverzeichnis::   Datentypen, Funktionen und Variable.

@detailmenu
 --- Detaillierte Liste der Knoten ---



Installation



* Aus Binärdatei installieren::  Guix installieren, ohne Zeit zu verlieren!
* Voraussetzungen::          Zum Erstellen und Benutzen von Guix nötige 
                               Software.
* Die Testsuite laufen lassen::  Guix testen.
* Den Daemon einrichten::    Wie man die Umgebung des Erstellungs-Daemons 
                               einrichtet.
* Aufruf des guix-daemon::   Den Erstellungs-Daemon laufen lassen.
* Anwendungen einrichten::   Anwendungsspezifische Einstellungen.

Den Daemon einrichten



* Einrichten der Erstellungsumgebung::  Die isolierte Umgebung zum Erstellen 
                                          vorbereiten.
* Auslagern des Daemons einrichten::  Erstellungen auf entfernte Maschinen 
                                        auslagern.
* SELinux-Unterstützung::   Wie man eine SELinux-Richtlinie für den Daemon 
                               einrichtet.

Paketverwaltung



* Funktionalitäten::        Wie Guix Ihr Leben schöner machen wird.
* Aufruf von guix package::  Pakete installieren, entfernen usw.
* Substitute::               Vorerstelle Binärdateien herunterladen.
* Pakete mit mehreren Ausgaben.::  Ein Quellpaket, mehrere Ausgaben.
* Aufruf von guix gc::       Den Müllsammler laufen lassen.
* Aufruf von guix pull::     Das neueste Guix samt Distribution laden.
* Channels::                 Customizing the package collection.
* Inferiors::                Interacting with another revision of Guix.
* Invoking guix describe::   Display information about your Guix revision.
* Aufruf von guix pack::     Software-Bündel erstellen.
* Aufruf von guix archive::  Import und Export von Store-Dateien.

Substitute



* Offizieller Substitut-Server::  Eine besondere Quelle von Substituten.
* Substitut-Server autorisieren::  Wie man Substitute an- und abschaltet.
* Substitutauthentifizierung::  Wie Guix Substitute verifiziert.
* Proxy-Einstellungen::      Wie Sie Substitute über einen Proxy beziehen.
* Fehler bei der Substitution::  Was passiert, wenn die Substitution 
                                   fehlschlägt.
* Vom Vertrauen gegenüber Binärdateien::  Wie können Sie diesem binären 
                                              Blob trauen?

Programmierschnittstelle



* Pakete definieren::        Wie Sie neue Pakete definieren.
* Erstellungssysteme::       Angeben, wie Pakete erstellt werden.
* Der Store::                Den Paket-Store verändern.
* Ableitungen::              Systemnahe Schnittstelle für Paketableitungen.
* Die Store-Monade::         Rein funktionale Schnittstelle zum Store.
* G-Ausdrücke::             Erstellungsausdrücke verarbeiten.
* Invoking guix repl::       Fiddling with Guix interactively.

Pakete definieren



* „package“-Referenz::   Der Datentyp für Pakete.
* „origin“-Referenz::    Datentyp für Paketursprünge.

Zubehör



* Aufruf von guix build::    Pakete aus der Befehlszeile heraus erstellen.
* Aufruf von guix edit::     Paketdefinitionen bearbeiten.
* Aufruf von guix download::  Herunterladen einer Datei und Ausgabe ihres 
                                Hashes.
* Aufruf von guix hash::     Den kryptographischen Hash einer Datei 
                               berechnen.
* Aufruf von guix import::   Paketdefinitionen importieren.
* Aufruf von guix refresh::  Paketdefinitionen aktualisieren.
* Aufruf von guix lint::     Fehler in Paketdefinitionen finden.
* Aufruf von guix size::     Plattenverbrauch profilieren.
* Aufruf von guix graph::    Den Paketgraphen visualisieren.
* Aufruf von guix environment::  Entwicklungsumgebungen einrichten.
* Aufruf von guix publish::  Substitute teilen.
* Aufruf von guix challenge::  Die Substitut-Server anfechten.
* Aufruf von guix copy::     Mit einem entfernten Store Dateien austauschen.
* Aufruf von guix container::  Prozesse isolieren.
* Aufruf von guix weather::  Die Verfügbarkeit von Substituten 
                               einschätzen.
* Invoking guix processes::  Listing client processes.

Aufruf von @command{guix build}



* Gemeinsame Erstellungsoptionen::  Erstellungsoptionen für die meisten 
                                      Befehle.
* Paketumwandlungsoptionen::  Varianten von Paketen erzeugen.
* Zusätzliche Erstellungsoptionen::  Optionen spezifisch für »guix 
                                        build«.
* Fehlschläge beim Erstellen untersuchen::  Praxiserfahrung bei der 
                                               Paketerstellung.

GNU-Distribution



* Systeminstallation::       Das ganze Betriebssystem installieren.
* Systemkonfiguration::      Das Betriebssystem konfigurieren.
* Dokumentation::            Wie man Nutzerhandbücher von Software liest.
* Dateien zur Fehlersuche installieren::  Womit man seinen Debugger 
                                            füttert.
* Sicherheitsaktualisierungen::  Sicherheits-Patches schnell einspielen.
* Paketmodule::              Pakete aus Sicht des Programmierers.
* Paketrichtlinien::         Die Distribution wachsen lassen.
* Bootstrapping::            GNU/Linux von Grund auf selbst erstellen.
* Portierung::               Guix auf andere Plattformen und Kernels 
                               bringen.

Systeminstallation



* Einschränkungen::         Was Sie erwarten dürfen.
* Hardware-Überlegungen::   Unterstützte Hardware.
* Installation von USB-Stick oder DVD::  Das Installationsmedium 
                                           vorbereiten.
* Vor der Installation::     Netzwerkanbindung, Partitionierung etc.
* Fortfahren mit der Installation::  Die Hauptsache.
* GuixSD in einer VM installieren::  Ein GuixSD-Spielplatz.
* Ein Abbild zur Installation erstellen::  Wie ein solches entsteht.

Systemkonfiguration



* Das Konfigurationssystems nutzen::  Ihr GNU-System anpassen
* „operating-system“-Referenz::  Details der 
                                       Betriebssystem-Deklarationen.
* Dateisysteme::             Die Dateisystemeinbindungen konfigurieren.
* Abgebildete Geräte::      Zusatzverarbeitungsschritte für blockbasierte 
                               Geräte.
* Benutzerkonten::           Benutzerkonten festlegen.
* Locales::                  Sprach- und kulturelle 
                               Konventionseinstellungen.
* Dienste::                  Systemdienste festlegen.
* Setuid-Programme::         Programme mit Administratorrechten ausführen
* X.509-Zertifikate::        HTTPS-Server authentifizieren.
* Name Service Switch::      Den Name Service Switch von libc konfigurieren.
* Initiale RAM-Disk::        Linux-libre hochfahren.
* Bootloader-Konfiguration::  Den Bootloader konfigurieren.
* Aufruf von guix system::   Instanzierung einer Systemkonfiguration
* GuixSD in einer VM starten::  Wie man GuixSD in einer virtuellen Maschine 
                                  startet.
* Dienste definieren::       Neue Dienstdefinitionen hinzufügen.

Dienste



* Basisdienste::             Essenzielle Systemdienste
* Geplante Auftragsausführung::  Der mcron-Dienst.
* Log-Rotation::             Der rottlog-Dienst.
* Netzwerkdienste::          Netzwerkeinrichtung, SSH-Daemon etc.
* X Window::                 Graphische Anzeige.
* Druckdienste::             Unterstützung für lokale und entfernte 
                               Drucker.
* Desktop-Dienste::          D-Bus- und Desktop-Dienste.
* Tondienste::               Dienste für ALSA und Pulseaudio.
* Datenbankdienste::         SQL-Datenbanken, Schlüssel-Wert-Speicher etc.
* Mail-Dienste::             IMAP, POP3, SMTP und so weiter.
* Kurznachrichtendienste::   Dienste für Kurznachrichten.
* Telefondienste::           Telefoniedienste.
* Überwachungsdienste::     Dienste zur Systemüberwachung.
* Kerberos-Dienste::         Kerberos-Dienste.
* Web-Dienste::              Web-Server.
* Zertifikatsdienste::       TLS-Zertifikate via Let’s Encrypt.
* DNS-Dienste::              DNS-Daemons.
* VPN-Dienste::              VPN-Daemons.
* Network File System::      Dienste mit Bezug zum Netzwerkdateisystem.
* Kontinuierliche Integration::  Der Cuirass-Dienst
* Power Management Services::  Extending battery life.
* Audio-Dienste::            Der MPD.
* Virtualisierungsdienste::  Dienste für virtuelle Maschinen.
* Versionskontrolldienste::  Entfernten Zugang zu Git-Repositorys bieten.
* Spieldienste::             Spielserver.
* Verschiedene Dienste::     Andere Dienste.

Dienste definieren



* Dienstkompositionen::      Wie Dienste zusammengestellt werden.
* Diensttypen und Dienste::  Typen und Dienste.
* Service-Referenz::         Referenz zur Programmierschnittstelle
* Shepherd-Dienste::         Eine spezielle Art von Dienst.

Paketrichtlinien



* Software-Freiheit::        Was in die Distribution aufgenommen werden 
                               darf.
* Paketbenennung::           Was macht einen Namen aus?
* Versionsnummern::          Wenn der Name noch nicht genug ist.
* Zusammenfassungen und Beschreibungen::  Den Nutzern helfen, das richtige 
                                            Paket zu finden.
* Python-Module::            Ein Touch britischer Comedy.
* Perl-Module::              Kleine Perlen.
* Java-Pakete::              Kaffeepause.
* Schriftarten::             Schriften verschriftlicht.

Mitwirken



* Erstellung aus dem Git::   Das Neueste und Beste.
* Guix vor der Installation ausführen::  Hacker-Tricks.
* Perfekt eingerichtet::     Die richtigen Werkzeuge.
* Code-Stil::                Wie Mitwirkende hygienisch arbeiten.
* Einreichen von Patches::   Teilen Sie Ihre Arbeit.

Code-Stil



* Programmierparadigmen::    Wie Sie Ihre Elemente zusammenstellen.
* Module::                   Wo Sie Ihren Code unterbringen.
* Datentypen und Mustervergleich::  Implementierung von Datenstrukturen.
* Formatierung von Code::    Schreibkonventionen.

@end detailmenu
@end menu

@c *********************************************************************
@node Einführung
@chapter Einführung

@cindex Zweck
GNU Guix@footnote{»Guix« wird wie »geeks« ausgesprochen, also als »ɡiːks« in
der Notation des Internationalen Phonetischen Alphabets (IPA).} ist ein
Werkzeug zur Paketverwaltung für das GNU-System. Guix macht es
unprivilegierten Nutzern leicht, Pakete zu installieren, zu aktualisieren
oder zu entfernen, zu einem vorherigen Satz von Paketen zurückzuwechseln,
Pakete aus ihrem Quellcode heraus zu erstellen und hilft allgemein bei der
Schöpfung und Wartung von Software-Umgebungen.

@cindex Benutzeroberflächen
Guix bietet eine kommandozeilenbasierte Paketverwaltungsschnittstelle
(@pxref{Aufruf von guix package}), einen Satz Befehlszeilenwerkzeuge
(@pxref{Zubehör}) sowie Schnittstellen zur Programmierung in Scheme
(@pxref{Programmierschnittstelle}).
@cindex Erstellungs-Daemon
Der @dfn{Erstellungs-Daemon} ist für das Erstellen von Paketen im Auftrag
von Nutzern verantwortlich (@pxref{Den Daemon einrichten}) und für das
Herunterladen vorerstellter Binärdateien aus autorisierten Quellen
(@pxref{Substitute}).

@cindex Erweiterbarkeit der Distribution
@cindex Anpassung, von Paketen
Guix enthält Paketdefinitionen für viele Pakete, von GNU und nicht von GNU,
die alle @uref{https://www.gnu.org/philosophy/free-sw.html, die Freiheit des
Computernutzers respektieren}. Es ist @emph{erweiterbar}: Nutzer können ihre
eigenen Paketdefinitionen schreiben (@pxref{Pakete definieren}) und sie als
unabhängige Paketmodule verfügbar machen (@pxref{Paketmodule}). Es ist
auch @emph{anpassbar}: Nutzer können spezialisierte Paketdefinitionen aus
bestehenden @emph{ableiten}, auch von der Befehlszeile (@pxref{Paketumwandlungsoptionen}).

@cindex Guix System Distribution
@cindex GuixSD
Sie können GNU@tie{}Guix auf ein bestehendes GNU/Linux-System aufsetzen, wo
es die bereits verfügbaren Werkzeuge ergänzt, ohne zu stören
(@pxref{Installation}), oder Sie können es eigenständig als Teil der
@dfn{Guix System Distribution}, kurz GuixSD (@pxref{GNU-Distribution}),
verwenden. Mit GNU@tie{}GuixSD @emph{deklarieren} Sie alle Aspekte der
Betriebssystemkonfiguration und Guix kümmert sich darum, die Konfiguration
oft transaktionsbasierte, reproduzierbare und zustandslose Weise zu
instanzieren (@pxref{Systemkonfiguration}).

@cindex funktionale Paketverwaltung
Intern implementiert Guix die Disziplin der @dfn{funktionalen
Paketverwaltung}, zu der Nix schon die Pionierarbeit geleistet hat
(@pxref{Danksagungen}). In Guix wird der Prozess, ein Paket zu erstellen
und zu installieren, als eine @emph{Funktion} im mathematischen Sinn
aufgefasst. Diese Funktion hat Eingaben, wie zum Beispiel
Erstellungs-Skripts, einen Compiler und Bibliotheken, und liefert ein
installiertes Paket. Als eine reine Funktion hängt sein Ergebnis allein von
seinen Eingaben ab — zum Beispiel kann er nicht auf Software oder Skripts
Bezug nehmen, die nicht ausdrücklich als Eingaben übergeben wurden. Eine
Erstellungsfunktion führt immer zum selben Ergebnis, wenn ihr die gleiche
Menge an Eingaben übergeben wurde. Sie kann die Umgebung des laufenden
Systems auf keine Weise beeinflussen, zum Beispiel kann sie keine Dateien
außerhalb ihrer Erstellungs- und Installationsverzeichnisse verändern. Um
dies zu erreichen, laufen Erstellungsprozesse in isolieren Umgebungen
(sogenannte @dfn{Container}), wo nur ausdrückliche Eingaben sichtbar sind.

@cindex Store
Das Ergebnis von Paketerstellungsfunktionen wird im Dateisystem
@dfn{zwischengespeichert} in einem besonderen Verzeichnis, was als @dfn{der
Store} bezeichnet wird (@pxref{Der Store}). Jedes Paket wird in sein eigenes
Verzeichnis im Store installiert — standardmäßig ist er unter
@file{/gnu/store} zu finden. Der Verzeichnisname enthält einen Hash aller
Eingaben, anhand derer das Paket erzeugt wurde, somit hat das Ändern einer
Eingabe einen völlig anderen Verzeichnisnamen zur Folge.

Dieses Vorgehen ist die Grundlage für die Guix auszeichnenden
Funktionalitäten: Unterstützung transaktionsbasierter Paketaktualisierungen
und -rückstufungen, Installation von Paketen als einfacher Nutzer sowie
Garbage Collection für Pakete (@pxref{Funktionalitäten}).


@c *********************************************************************
@node Installation
@chapter Installation

@cindex Guix installieren
GNU Guix kann von seiner Webseite unter
@url{http://www.gnu.org/software/guix/} heruntergeladen werden. Dieser
Abschnitt beschreibt die Software-Voraussetzungen von Guix und wie man es
installiert, so dass man es benutzen kann.

Beachten Sie, dass es in diesem Abschnitt um die Installation des
Paketverwaltungswerkzeugs geht, welche auf einem laufenden GNU/Linux-System
vollzogen werden kann. Falls Sie stattdessen das vollständige
GNU-Betriebssystem installieren möchten, werfen Sie einen Blick in den
Abschnitt @pxref{Systeminstallation}.

@cindex Fremddistribution
Wenn es auf ein bestehendes GNU/Linux-System installiert wird — im Folgenden
als @dfn{Fremddistribution} bezeichnet —, ergänzt GNU@tie{}Guix die
verfügbaren Werkzeuge, ohne dass sie sich gegenseitig stören. Guix’ Daten
befinden sich ausschließlich in zwei Verzeichnissen, üblicherweise
@file{/gnu/store} und @file{/var/guix}; andere Dateien auf Ihrem System wie
@file{/etc} bleiben unberührt.

Sobald es installiert ist, kann Guix durch Ausführen von @command{guix pull}
aktualisiert werden (@pxref{Aufruf von guix pull}).

@menu
* Aus Binärdatei installieren::  Guix installieren, ohne Zeit zu verlieren!
* Voraussetzungen::          Zum Erstellen und Benutzen von Guix nötige 
                               Software.
* Die Testsuite laufen lassen::  Guix testen.
* Den Daemon einrichten::    Wie man die Umgebung des Erstellungs-Daemons 
                               einrichtet.
* Aufruf des guix-daemon::   Den Erstellungs-Daemon laufen lassen.
* Anwendungen einrichten::   Anwendungsspezifische Einstellungen.
@end menu

@node Aus Binärdatei installieren
@section Aus Binärdatei installieren

@cindex Guix aus Binärdateien installieren
Dieser Abschnitt beschreibt, wie sich Guix auf einem beliebigen System aus
einem alle Komponenten umfassenden Tarball installieren lässt, der
Binärdateien für Guix und all seine Abhängigkeiten liefert. Dies geht in der
Regel schneller, als Guix aus seinen Quelldateien zu installieren, was im
nächsten Abschnitt beschrieben wird. Vorausgesetzt wird hier lediglich, dass
GNU@tie{}tar und Xz verfügbar sind.

Wir bieten ein
@uref{https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh,
Installations-Skript für die Shell}, welches Guix automatisch herunterlädt,
installiert und eine erste Konfiguration von Guix mit sich bringt. Es sollte
als der Administratornutzer (als »root«) ausgeführt werden.

Die Installation läuft so ab:

@enumerate
@item
@cindex Guix-Binärdatei herunterladen
Download the binary tarball from
@indicateurl{https://alpha.gnu.org/gnu/guix/guix-binary-@value{VERSION}.@var{system}.tar.xz},
where @var{system} is @code{x86_64-linux} for an @code{x86_64} machine
already running the kernel Linux, and so on.

@c The following is somewhat duplicated in ``System Installation''.
Achten Sie darauf, auch die zugehörige @file{.sig}-Datei herunterzuladen und
verifizieren Sie damit die Authentizität des Tarballs, ungefähr so:

@example
$ wget https://alpha.gnu.org/gnu/guix/guix-binary-@value{VERSION}.@var{system}.tar.xz.sig
$ gpg --verify guix-binary-@value{VERSION}.@var{system}.tar.xz.sig
@end example

Falls dieser Befehl fehlschlägt, weil Sie nicht über den nötigen
öffentlichen Schlüssel verfügen, können Sie ihn mit diesem Befehl
importieren:

@example
$ gpg --keyserver pgp.mit.edu --recv-keys @value{OPENPGP-SIGNING-KEY-ID}
@end example

@noindent
@c end authentication part
und den Befehl @code{gpg --verify} erneut ausführen.

@item
Nun müssen Sie zum Administratornutzer @code{root} wechseln. Abhängig von
Ihrer Distribution müssen Sie dazu etwa @code{su -} oder @code{sudo -i}
ausführen. Danach führen Sie als @code{root}-Nutzer aus:

@example
# cd /tmp
# tar --warning=no-timestamp -xf \
     guix-binary-@value{VERSION}.@var{system}.tar.xz
# mv var/guix /var/ && mv gnu /
@end example

Dadurch wird @file{/gnu/store} (@pxref{Der Store}) und @file{/var/guix}
erzeugt. Letzteres enthält ein Profil, welches bereit zur Nutzung durch
@code{root} ist (wie im nächsten Schritt beschrieben).

Entpacken Sie den Tarball @emph{nicht} auf einem schon funktionierenden
Guix-System, denn es würde seine eigenen essenziellen Dateien überschreiben.

Die Befehlszeilenoption @code{--warning=no-timestamp} stellt sicher, dass
GNU@tie{}tar nicht vor »unplausibel alten Zeitstempeln« warnt (solche
Warnungen traten bei GNU@tie{}tar 1.26 und älter auf, neue Versionen machen
keine Probleme). Sie kommen daher, dass alle Dateien im Archiv als
Änderungszeitpunkt null eingetragen bekommen haben (das bezeichnet den
1. Januar 1970). Das ist Absicht, damit der Inhalt des Archivs nicht davon
abhängt, wann es erstellt wurde, und es somit reproduzierbar wird.

@item
Machen Sie das Profil von @code{root} verfügbar als
@file{~root/.guix-profile}:

@example
# ln -sf /var/guix/profiles/per-user/root/guix-profile \
         ~root/.guix-profile
@end example

»Sourcen« Sie @file{etc/profile}, um @code{PATH} und andere relevante
Umgebungsvariable zu ergänzen:

@example
# GUIX_PROFILE="`echo ~root`/.guix-profile" ; \
  source $GUIX_PROFILE/etc/profile
@end example

@item
Erzeugen Sie Nutzergruppe und Nutzerkonten für die Erstellungs-Benutzer wie
folgt (@pxref{Einrichten der Erstellungsumgebung}).

@item
Führen Sie den Daemon aus, und lassen Sie ihn automatisch bei jedem
Hochfahren starten.

Wenn Ihre Wirts-Distribution systemd als »init«-System verwendet, können Sie
das mit folgenden Befehlen veranlassen:

@c Versions of systemd that supported symlinked service files are not
@c yet widely deployed, so we should suggest that users copy the service
@c files into place.
@c
@c See this thread for more information:
@c http://lists.gnu.org/archive/html/guix-devel/2017-01/msg01199.html

@example
# cp ~root/.guix-profile/lib/systemd/system/guix-daemon.service \
        /etc/systemd/system/
# systemctl start guix-daemon && systemctl enable guix-daemon
@end example

Wenn Ihre Wirts-Distribution als »init«-System Upstart verwendet:

@example
# initctl reload-configuration
# cp ~root/.guix-profile/lib/upstart/system/guix-daemon.conf /etc/init/
# start guix-daemon
@end example

Andernfalls können Sie den Daemon immer noch manuell starten, mit:

@example
# ~root/.guix-profile/bin/guix-daemon --build-users-group=guixbuild
@end example

@item
Stellen Sie den @command{guix}-Befehl auch anderen Nutzern Ihrer Maschine
zur Verfügung, zum Beispiel so:

@example
# mkdir -p /usr/local/bin
# cd /usr/local/bin
# ln -s /var/guix/profiles/per-user/root/guix-profile/bin/guix
@end example

Es ist auch eine gute Idee, die Info-Version dieses Handbuchs ebenso
verfügbar zu machen:

@example
# mkdir -p /usr/local/share/info
# cd /usr/local/share/info
# for i in /var/guix/profiles/per-user/root/guix-profile/share/info/* ;
  do ln -s $i ; done
@end example

Auf diese Art wird, unter der Annahme, dass bei Ihnen
@file{/usr/local/share/info} im Suchpfad eingetragen ist, das Ausführen von
@command{info guix} dieses Handbuch öffnen (@pxref{Other Info Directories,,,
texinfo, GNU Texinfo} hat weitere Details, wie Sie den Info-Suchpfad ändern
können).

@item
@cindex Substitute, deren Autorisierung
Um Substitute von @code{hydra.gnu.org} oder einem Spiegelserver davon zu
benutzen (@pxref{Substitute}), müssen sie erst autorisiert werden:

@example
# guix archive --authorize < ~root/.guix-profile/share/guix/hydra.gnu.org.pub
@end example

@item
Alle Nutzer müssen womöglich ein paar zusätzliche Schritte ausführen, damit
ihre Guix-Umgebung genutzt werden kann, siehe @pxref{Anwendungen einrichten}.
@end enumerate

Voilà, die installation ist fertig!

Sie können nachprüfen, dass Guix funktioniert, indem Sie ein Beispielpaket
in das root-Profil installieren:

@example
# guix package -i hello
@end example

The @code{guix} package must remain available in @code{root}'s profile, or
it would become subject to garbage collection---in which case you would find
yourself badly handicapped by the lack of the @command{guix} command.  In
other words, do not remove @code{guix} by running @code{guix package -r
guix}.

Der Tarball zur Installation aus einer Binärdatei kann einfach durch
Ausführung des folgenden Befehls im Guix-Quellbaum (re-)produziert und
verifiziert werden:

@example
make guix-binary.@var{system}.tar.xz
@end example

@noindent
…was wiederum dies ausführt:

@example
guix pack -s @var{system} --localstatedir guix
@end example

Siehe @xref{Aufruf von guix pack} für weitere Informationen zu diesem
praktischen Werkzeug.

@node Voraussetzungen
@section Voraussetzungen

Dieser Abschnitt listet Voraussetzungen auf, um Guix aus seinem Quellcode zu
erstellen. Der Erstellungsprozess für Guix ist derselbe wie für andere
GNU-Software und wird hier nicht beschrieben. Bitte lesen Sie die Dateien
@file{README} und @file{INSTALL} im Guix-Quellbaum, um weitere Details zu
erfahren.

GNU Guix hat folgende Pakete als Abhängigkeiten:

@itemize
@item @url{http://gnu.org/software/guile/, GNU Guile}, Version 2.0.13 oder
neuer, einschließlich 2.2.x,
@item @url{https://notabug.org/cwebber/guile-gcrypt, Guile-Gcrypt}, version
0.1.0 or later;
@item
@uref{http://gnutls.org/, GnuTLS}, im Speziellen dessen Bindungen für Guile
(@pxref{Guile Preparations, how to install the GnuTLS bindings for Guile,,
gnutls-guile, GnuTLS-Guile}),
@item
@uref{https://notabug.org/civodul/guile-sqlite3, Guile-SQLite3}, version
0.1.0 or later;
@item
@c FIXME: Specify a version number once a release has been made.
@uref{https://gitlab.com/guile-git/guile-git, Guile-Git}, vom August 2017
oder neuer,
@item @url{http://zlib.net, zlib},
@item @url{http://www.gnu.org/software/make/, GNU Make}.
@end itemize

Folgende Abhängigkeiten sind optional:

@itemize
@item
Wenn Sie @url{http://savannah.nongnu.org/projects/guile-json/, Guile-JSON}
installieren, können Sie den Befehl @command{guix import pypi} benutzen
(@pxref{Aufruf von guix import}). Das spielt hauptsächlich für Entwickler und
nicht für Gelegenheitsnutzer eine Rolle.

@item
@c Note: We need at least 0.10.2 for 'channel-send-eof'.
Unterstützung für das Auslagern von Erstellungen (@pxref{Auslagern des Daemons einrichten}) und @command{guix copy} (@pxref{Aufruf von guix copy}) hängt von
@uref{https://github.com/artyom-poptsov/guile-ssh, Guile-SSH}, Version
0.10.2 oder neuer, ab.

@item
Wenn @url{http://www.bzip.org, libbz2} verfügbar ist, kann
@command{guix-daemon} damit Erstellungsprotokolle komprimieren.
@end itemize

Sofern nicht @code{--disable-daemon} beim Aufruf von @command{configure}
übergeben wurde, benötigen Sie auch folgende Pakete:

@itemize
@item @url{http://gnupg.org/, GNU libgcrypt},
@item @url{http://sqlite.org, SQLite 3},
@item @url{http://gcc.gnu.org, GCC's g++} mit Unterstützung für den
C++11-Standard.
@end itemize

@cindex Zustandsverzeichnis
Sollten Sie Guix auf einem System konfigurieren, auf dem Guix bereits
installiert ist, dann stellen Sie sicher, dasselbe Zustandsverzeichnis wie
für die bestehende Installation zu verwenden. Benutzen Sie dazu die
Befehlszeilenoption @code{--localstatedir} des @command{configure}-Skripts
(@pxref{Directory Variables, @code{localstatedir},, standards, GNU Coding
Standards}). Das @command{configure}-Skript schützt vor ungewollter
Fehlkonfiguration der @var{localstatedir}, damit sie nicht versehentlich
Ihren Store verfälschen (@pxref{Der Store}).

@cindex Nix, Kompatibilität
Wenn eine funktionierende Installation of @url{http://nixos.org/nix/, the
Nix package manager} verfügbar ist, können Sie Guix stattdessen mit
@code{--disable-daemon} konfigurieren. In diesem Fall ersetzt Nix die drei
obengenannten Abhängigkeiten.

Guix ist mit Nix kompatibel, daher ist es möglich, denselben Store für beide
zu verwenden. Dazu müssen Sie an @command{configure} nicht nur denselben
Wert für @code{--with-store-dir} übergeben, sondern auch denselben Wert für
@code{--localstatedir}. Letzterer ist deswegen essenziell, weil er unter
Anderem angibt, wo die Datenbank liegt, in der sich die Metainformationen
über den Store befinden. Für Nix sind die Werte standardmäßig
@code{--with-store-dir=/nix/store} und
@code{--localstatedir=/nix/var}. Beachten Sie, dass @code{--disable-daemon}
nicht erforderlich ist, wenn Sie die Absicht haben, den Store mit Nix zu
teilen.

@node Die Testsuite laufen lassen
@section Die Testsuite laufen lassen

@cindex Testkatalog
Nachdem @command{configure} und @code{make} erfolgreich durchgelaufen sind,
ist es ratsam, den Testkatalog auszuführen. Er kann dabei helfen, Probleme
mit der Einrichtung oder Systemumgebung zu finden, oder auch Probleme in
Guix selbst — und Testfehler zu melden ist eine wirklich gute Art und Weise,
bei der Verbesserung von Guix mitzuhelfen. Um den Testkatalog auszuführen,
geben Sie Folgendes ein:

@example
make check
@end example

Testfälle können parallel ausgeführt werden. Sie können die
Befehlszeiltenoption @code{-j} von GNU@tie{}make benutzen, damit es
schneller geht. Der erste Durchlauf kann auf neuen Maschinen ein paar
Minuten dauern, nachfolgende Ausführungen werden schneller sein, weil der
für die Tests erstellte Store schon einige Dinge zwischengespeichert haben
wird.

Es ist auch möglich, eine Teilmenge der Tests laufen zu lassen, indem Sie
die @code{TESTS}-Variable des Makefiles ähnlich wie in diesem Beispiel
definieren:

@example
make check TESTS="tests/store.scm tests/cpio.scm"
@end example

Standardmäßig werden Testergebnisse pro Datei angezeigt. Um die Details
jedes einzelnen Testfalls zu sehen, können Sie wie in diesem Beispiel die
@code{SCM_LOG_DRIVER_FLAGS}-Variable des Makefiles definieren:

@example
make check TESTS="tests/base64.scm" SCM_LOG_DRIVER_FLAGS="--brief=no"
@end example

Kommt es zum Fehlschlag, senden Sie bitte eine E-mail an
@email{bug-guix@@gnu.org} und fügen Sie die Datei @file{test-suite.log} als
Anhang bei. Bitte geben Sie dabei in Ihrer Nachricht die benutze Version von
Guix an sowie die Versionsnummern der Abhängigkeiten (@pxref{Voraussetzungen}).

Guix wird auch mit einem Testkatalog für das ganze System ausgeliefert, der
vollständige Instanzen des GuixSD-Betriebssystems testet. Er kann nur auf
Systemen benutzt werden, auf denen Guix bereits installiert ist, mit
folgendem Befehl:

@example
make check-system
@end example

@noindent
Oder, auch hier, indem Sie @code{TESTS} definieren, um eine Teilmenge der
auszuführenden Tests anzugeben:

@example
make check-system TESTS="basic mcron"
@end example

Diese Systemtests sind in den @code{(gnu tests @dots{})}-Modulen
definiert. Sie funktionieren, indem Sie das getestete Betriebssystem mitsamt
schlichter Instrumentierung in einer virtuellen Maschine (VM) ausführen. Die
Tests können aufwendige Berechnungen durchführen oder sie günstig umgehen,
je nachdem, ob für ihre Abhängigkeiten Substitute zur Verfügung stehen
(@pxref{Substitute}). Manche von ihnen nehmen viel Speicherplatz in
Anspruch, um die VM-Abbilder zu speichern.

Auch hier gilt: Falls Testfehler auftreten, senden Sie bitte alle Details an
@email{bug-guix@@gnu.org}.

@node Den Daemon einrichten
@section Den Daemon einrichten

@cindex Daemon
Operationen wie das Erstellen eines Pakets oder Laufenlassen des
Müllsammlers werden alle durch einen spezialisierten Prozess durchgeführt,
den @dfn{Erstellungs-Daemon}, im Auftrag seiner Kunden (Clients). Nur der
Daemon darf auf den Store und seine zugehörige Datenbank zugreifen. Daher
wird jede den Store verändernde Operation durch den Daemon durchgeführt. Zum
Beispiel kommunizieren Befehlszeilenwerkzeuge wie @command{guix package} und
@command{guix build} mit dem Daemon (mittels entfernter Prozeduraufrufe), um
ihm Anweisungen zu geben, was er tun soll.

Folgende Abschnitte beschreiben, wie Sie die Umgebung des
Erstellungs-Daemons ausstatten sollten. Siehe auch @ref{Substitute} für
Informationen darüber, wie Sie es dem Daemon ermöglichen, vorerstellte
Binärdateien herunterzuladen.

@menu
* Einrichten der Erstellungsumgebung::  Die isolierte Umgebung zum Erstellen 
                                          vorbereiten.
* Auslagern des Daemons einrichten::  Erstellungen auf entfernte Maschinen 
                                        auslagern.
* SELinux-Unterstützung::   Wie man eine SELinux-Richtlinie für den Daemon 
                               einrichtet.
@end menu

@node Einrichten der Erstellungsumgebung
@subsection Einrichten der Erstellungsumgebung

@cindex Erstellungsumgebung
In einem normalen Mehrbenutzersystem werden Guix und sein Daemon — das
Programm @command{guix-daemon} — vom Systemadministrator installiert;
@file{/gnu/store} gehört @code{root} und @command{guix-daemon} läuft als
@code{root}. Nicht mit erweiterten Rechten ausgestattete Nutzer können
Guix-Werkzeuge benutzen, um Pakete zu erstellen oder anderweitig auf den
Store zuzugreifen, und der Daemon wird dies für sie erledigen und dabei
sicherstellen, dass der Store in einem konsistenten Zustand verbleibt und
sich die Nutzer erstellte Pakete teilen.

@cindex Erstellungsbenutzer
Wenn @command{guix-daemon} als Administratornutzer @code{root} läuft, wollen
Sie aber vielleicht dennoch nicht, dass Paketerstellungsprozesse auch als
@code{root} ablaufen, aus offensichtlichen Sicherheitsgründen. Um dies zu
vermeiden, sollte ein besonderer Pool aus @dfn{Erstellungsbenutzern}
geschaffen werden, damit vom Daemon gestartete Erstellungsprozesse ihn
benutzen. Diese Erstellungsbenutzer müssen weder eine Shell noch einen
Persönlichen Ordner zugewiesen bekommen, sie werden lediglich benutzt, wenn
der Daemon @code{root}-Rechte in Erstellungsprozessen ablegt. Mehrere solche
Benutzer zu haben, ermöglicht es dem Daemon, verschiedene
Erstellungsprozessen unter verschiedenen Benutzeridentifikatoren (UIDs) zu
starten, was garantiert, dass sie einander nicht stören — eine essenzielle
Funktionalität, da Erstellungen als reine Funktionen angesehen werden
(@pxref{Einführung}).

Auf einem GNU/Linux-System kann ein Pool von Erstellungsbenutzern wie folgt
erzeugt werden (mit Bash-Syntax und den Befehlen von @code{shadow}):

@c See http://lists.gnu.org/archive/html/bug-guix/2013-01/msg00239.html
@c for why `-G' is needed.
@example
# groupadd --system guixbuild
# for i in `seq -w 1 10`;
  do
    useradd -g guixbuild -G guixbuild                  \
            -d /var/empty -s `which nologin`           \
            -c "Guix-Erstellungsbenutzer $i" --system  \
            guixbuilder$i;
  done
@end example

@noindent
Die Anzahl der Erstellungsbenutzer entscheidet, wieviele Erstellungsaufträge
parallel ausgeführt werden können, wie es mit der Befehlszeilenoption
@option{--max-jobs} vorgeben werden kann (@pxref{Aufruf des guix-daemon,
@option{--max-jobs}}). Um @command{guix system vm} und ähnliche Befehle
nutzen zu können, müssen Sie die Erstellungsbenutzer unter Umständen zur
@code{kvm}-Benutzergruppe hinzufügen, damit sie Zugriff auf @file{/dev/kvm}
haben, mit @code{-G guixbuild,kvm} statt @code{-G guixbuild}
(@pxref{Aufruf von guix system}).

Das Programm @code{guix-daemon} kann mit dem folgenden Befehl als
@code{root} gestartet werden@footnote{Wenn Ihre Maschine systemd als
»init«-System verwendet, genügt es, die Datei
@file{@var{prefix}/lib/systemd/system/guix-daemon.service} in
@file{/etc/systemd/system} zu platzieren, damit @command{guix-daemon}
automatisch gestartet wird. Ebenso können Sie, wenn Ihre Maschine Upstart
als »init«-System benutzt, die Datei
@file{@var{prefix}/lib/upstart/system/guix-daemon.conf} in @file{/etc/init}
platzieren.}:

@example
# guix-daemon --build-users-group=guixbuild
@end example

@cindex chroot
@noindent
Auf diese Weise startet der Daemon Erstellungsprozesse in einem chroot als
einer der @code{guixbuilder}-Benutzer. Auf GNU/Linux enthält die
chroot-Umgebung standardmäßig nichts außer:

@c Keep this list in sync with libstore/build.cc! -----------------------
@itemize
@item
einem minimalen @code{/dev}-Verzeichnis, was größtenteils vom @code{/dev}
des Wirtssystems unabhängig erstellt wurde@footnote{»Größtenteils«, denn
obwohl die Menge an Dateien, die im @code{/dev} des chroots vorkommen, fest
ist, können die meisten dieser Dateien nur dann erstellt werden, wenn das
Wirtssystem sie auch hat.},

@item
dem @code{/proc}-Verzeichnis, es zeigt nur die Prozesse des Containers, weil
ein separater Namensraum für Prozess-IDs (PIDs) benutzt wird,

@item
@file{/etc/passwd} mit einem Eintrag für den aktuellen Benutzer und einem
Eintrag für den Benutzer @file{nobody},

@item
@file{/etc/group} mit einem Eintrag für die Gruppe des Benutzers,

@item
@file{/etc/hosts} mit einem Eintrag, der @code{localhost} auf
@code{127.0.0.1} abbildet,

@item
einem @file{/tmp}-Verzeichnis mit Schreibrechten.
@end itemize

Sie können beeinflussen, in welchem Verzeichnis der Daemon Erstellungsbäume
unterbringt, indem sie den Wert der Umgebungsvariablen @code{TMPDIR}
ändern. Allerdings heißt innerhalb des chroots der Erstellungsbaum immer
@file{/tmp/guix-build-@var{name}.drv-0}, wobei @var{name} der Ableitungsname
ist — z.B. @code{coreutils-8.24}. Dadurch hat der Wert von @code{TMPDIR}
keinen Einfluss auf die Erstellungsumgebung, wodurch Unterschiede vermieden
werden, falls Erstellungsprozesse den Namen ihres Erstellungsbaumes
einfangen.

@vindex http_proxy
Der Daemon befolgt außerdem den Wert der Umgebungsvariablen
@code{http_proxy} für von ihm durchgeführte HTTP-Downloads, sei es für
Ableitungen mit fester Ausgabe (@pxref{Ableitungen}) oder für Substitute
(@pxref{Substitute}).

Wenn Sie Guix als ein Benutzer ohne erweiterte Rechte installieren, ist es
dennoch möglich, @command{guix-daemon} auszuführen, sofern Sie
@code{--disable-chroot} übergeben. Allerdings können Erstellungsprozesse
dann nicht voneinander und vom Rest des Systems isoliert werden. Daher
können sich Erstellungsprozesse gegenseitig stören und auf Programme,
Bibliotheken und andere Dateien zugreifen, die dem restlichen System zur
Verfügung stehen — was es deutlich schwerer macht, die als @emph{reine}
Funktionen aufzufassen.


@node Auslagern des Daemons einrichten
@subsection Nutzung der Auslagerungsfunktionalität

@cindex auslagern
@cindex Build-Hook
Wenn erwünscht kann der Erstellungs-Daemon Ableitungserstellungen
@dfn{auslagern} auf andere Maschinen, auf denen Guix läuft, mit Hilfe des
@code{offload}-»@dfn{Build-Hooks}«@footnote{Diese Funktionalität ist nur
verfügbar, wenn @uref{https://github.com/artyom-poptsov/guile-ssh,
Guile-SSH} vorhanden ist.}. Wenn diese Funktionalität aktiviert ist, wird
eine nutzerspezifizierte Liste von Erstellungsmaschinen aus
@file{/etc/guix/machines.scm} gelesen. Wann immer eine Erstellung angefragt
wird, zum Beispiel durch @code{guix build}, versucht der Daemon, sie an eine
der Erstellungsmaschinen auszulagern, die die Einschränkungen der Ableitung
erfüllen, insbesondere ihren Systemtyp — z.B. @file{x86_64-linux}. Fehlende
Voraussetzungen für die Erstellung werden über SSH auf die Zielmaschine
kopiert, welche dann mit der Erstellung weitermacht. Hat sie Erfolg damit,
so werden die Ausgabe oder Ausgaben der Erstellung zurück auf die
ursprüngliche Maschine kopiert.

Die Datei @file{/etc/guix/machines.scm} sieht normalerweise so aus:

@example
(list (build-machine
        (name "eightysix.example.org")
        (system "x86_64-linux")
        (host-key "ssh-ed25519 AAAAC3Nza@dots{}")
        (user "bob")
        (speed 2.))     ;unglaublich schnell!

      (build-machine
        (name "meeps.example.org")
        (system "mips64el-linux")
        (host-key "ssh-rsa AAAAB3Nza@dots{}")
        (user "alice")
        (private-key
         (string-append (getenv "HOME")
                        "/.ssh/identität-für-guix"))))
@end example

@noindent
Im obigen Beispiel geben wir eine Liste mit zwei Erstellungsmaschinen vor,
eine für die @code{x86_64}-Architektur und eine für die
@code{mips64el}-Architektur.

Tatsächlich ist diese Datei — wenig überraschend! — eine Scheme-Datei, die
ausgewertet wird, wenn der @code{offload}-Hook gestartet wird. Der Wert, den
sie zurückliefert, muss eine Liste von @code{build-machine}-Objekten
sein. Obwohl dieses Beispiel eine feste Liste von Erstellungsmaschinen
zeigt, könnte man auch auf die Idee kommen, etwa mit DNS-SD eine Liste
möglicher im lokalen Netzwerk entdeckter Erstellungsmaschinen zu liefern
(@pxref{Einführung, Guile-Avahi,, guile-avahi, Using Avahi in Guile Scheme
Programs}). Der Datentyp @code{build-machine} wird im Folgenden weiter
ausgeführt.

@deftp {Datentyp} build-machine
Dieser Datentyp repräsentiert Erstellungsmaschinen, an die der Daemon
Erstellungen auslagern darf. Die wichtigen Felder sind:

@table @code

@item name
Der Hostname der entfernten Maschine.

@item system
Der Systemtyp der entfernten Maschine — z.B. @code{"x86_64-linux"}.

@item user
Das Benutzerkonto, mit dem eine Verbindung zur entfernten Maschine über SSH
aufgebaut werden soll. Beachten Sie, dass das SSH-Schlüsselpaart
@emph{nicht} durch eine Passphrase geschützt sein darf, damit
nicht-interaktive Anmeldungen möglich sind.

@item host-key
Dies muss der @dfn{öffentliche SSH-Host-Schlüssel} der Maschine im
OpenSSH-Format sein. Er wird benutzt, um die Identität der Maschine zu
prüfen, wenn wir uns mit ihr verbinden. Er ist eine lange Zeichenkette, die
ungefähr so aussieht:

@example
ssh-ed25519 AAAAC3NzaC@dots{}mde+UhL hint@@example.org
@end example

Wenn auf der Maschine der OpenSSH-Daemon, @command{sshd}, läuft, ist der
Host-Schlüssel in einer Datei wie @file{/etc/ssh/ssh_host_ed25519_key.pub}
zu finden.

Wenn auf der Maschine der SSH-Daemon von GNU@tie{}lsh, nämlich
@command{lshd}, läuft, befindet sich der Host-Schlüssel in
@file{/etc/lsh/host-key.pub} oder einer ähnlichen Datei. Er kann ins
OpenSSH-Format umgewandelt werden durch @command{lsh-export-key}
(@pxref{Converting keys,,, lsh, LSH Manual}):

@example
$ lsh-export-key --openssh < /etc/lsh/host-key.pub 
ssh-rsa AAAAB3NzaC1yc2EAAAAEOp8FoQAAAQEAs1eB46LV@dots{}
@end example

@end table

Eine Reihe optionaler Felder kann festgelegt werden:

@table @asis

@item @code{port} (Vorgabe: @code{22})
Portnummer des SSH-Servers auf der Maschine.

@item @code{private-key} (Vorgabe: @file{~root/.ssh/id_rsa})
The SSH private key file to use when connecting to the machine, in OpenSSH
format.  This key must not be protected with a passphrase.

Beachten Sie, dass als Vorgabewert der private Schlüssel @emph{des
root-Benutzers} genommen wird. Vergewissern Sie sich, dass er existiert,
wenn Sie die Standardeinstellung verwenden.

@item @code{compression} (Vorgabe: @code{"zlib@@openssh.com,zlib"})
@itemx @code{compression-level} (Vorgabe: @code{3})
Die Kompressionsmethoden auf SSH-Ebene und das angefragte
Kompressionsniveau.

Beachten Sie, dass Auslagerungen SSH-Kompression benötigen, um beim
Übertragen von Dateien an Erstellungsmaschinen und zurück weniger Bandbreite
zu benutzen.

@item @code{daemon-socket} (Vorgabe: @code{"/var/guix/daemon-socket/socket"})
Dateiname des Unix-Sockets, auf dem @command{guix-daemon} auf der Maschine
lauscht.

@item @code{parallel-builds} (Vorgabe: @code{1})
Die Anzahl der Erstellungen, die auf der Maschine parallel ausgeführt werden
können.

@item @code{speed} (Vorgabe: @code{1.0})
Ein »relativer Geschwindigkeitsfaktor«. Der Auslagerungsplaner gibt
tendenziell Maschinen mit höherem Geschwindigkeitsfaktor den Vorrang.

@item @code{features} (Vorgabe: @code{'()})
Eine Liste von Zeichenketten, die besondere von der Maschine unterstützte
Funktionalitäten bezeichnen. Ein Beispiel ist @code{"kvm"} für Maschinen,
die über die KVM-Linux-Module zusammen mit entsprechender
Hardware-Unterstützung verfügen. Ableitungen können Funktionalitäten dem
Namen nach anfragen und werden dann auf passenden Erstellungsmaschinen
eingeplant.

@end table
@end deftp

Der Befehl @code{guile} muss sich im Suchpfad der Erstellungsmaschinen
befinden. Zusätzlich müssen die Guix-Module im @code{$GUILE_LOAD_PATH} auf
den Erstellungsmaschinen zu finden sein — um dies nachzuprüfen, können Sie
Folgendes ausführen:

@example
ssh build-machine guile -c "'(use-modules (guix config))'"
@end example

Es gibt noch eine weitere Sache zu tun, sobald @file{machines.scm}
eingerichtet ist. Wie zuvor erklärt, werden beim Auslagern Dateien zwischen
den Stores der Maschinen hin- und hergeschickt. Damit das funktioniert,
müssen Sie als Erstes ein Schlüsselpaar auf jeder Maschine erzeugen, damit
der Daemon signierte Archive mit den Dateien aus dem Store versenden kann
(@pxref{Aufruf von guix archive}):

@example
# guix archive --generate-key
@end example

@noindent
Jede Erstellungsmaschine muss den Schlüssel der Hauptmaschine autorisieren,
damit diese Store-Objekte von der Hauptmaschine empfangen kann:

@example
# guix archive --authorize < öffentlicher-schlüssel-hauptmaschine.txt
@end example

@noindent
Andersherum muss auch die Hauptmaschine den jeweiligen Schlüssel jeder
Erstellungsmaschine autorisieren.

Der ganze Umstand mit den Schlüsseln soll ausdrücken, dass sich Haupt- und
Erstellungsmaschinen paarweise gegenseitig vertrauen. Konkret kann der
Erstellungs-Daemon auf der Hauptmaschine die Echtheit von den
Erstellungsmaschinen empfangener Dateien gewährleisten (und umgekehrt), und
auch dass sie nicht sabotiert wurden und mit einem autorisierten Schlüssel
signiert wurden.

@cindex Auslagerung testen
Um zu testen, ob Ihr System funktioniert, führen Sie diesen Befehl auf der
Hauptmaschine aus:

@example
# guix offload test
@end example

Dadurch wird versucht, zu jeder Erstellungsmaschine eine Verbindung
herzustellen, die in @file{/etc/guix/machines.scm} angegeben wurde,
sichergestellt, dass auf jeder Guile und die Guix-Module nutzbar sind, und
jeweils versucht, etwas auf die Erstellungsmaschine zu exportieren und von
dort zu imporieren. Dabei auftretende Fehler werden gemeldet.

Wenn Sie stattdessen eine andere Maschinendatei verwenden möchten, geben Sie
diese einfach auf der Befehlszeile an:

@example
# guix offload test maschinen-qualif.scm
@end example

Letztendlich können Sie hiermit nur die Teilmenge der Maschinen testen,
deren Name zu einem regulären Ausdruck passt:

@example
# guix offload test maschinen.scm '\.gnu\.org$'
@end example

@cindex Auslagerungs-Lagebericht
Um die momentane Auslastung aller Erstellungs-Hosts anzuzeigen, führen Sie
diesen Befehl auf dem Hauptknoten aus:

@example
# guix offload status
@end example


@node SELinux-Unterstützung
@subsection SELinux-Unterstützung

@cindex SELinux, Policy für den Daemon
@cindex Mandatory Access Control, SELinux
@cindex Sicherheit, des guix-daemon
Guix enthält eine SELinux-Richtliniendatei (»Policy«) unter
@file{etc/guix-daemon.cil}, die auf einem System installiert werden
kann, auf dem SELinux aktiviert ist, damit Guix-Dateien gekennzeichnet
sind, und um das erwartete Verhalten des Daemons anzugeben. Da GuixSD
keine Grundrichtlinie (»Base Policy«) für SELinux bietet, kann diese
Richtlinie für den Daemon auf GuixSD nicht benutzt werden.

@subsubsection Installieren der SELinux-Policy
@cindex SELinux, Policy installieren
Um die Richtlinie (Policy) zu installieren, führen Sie folgenden Befehl mit
Administratorrechten aus:

@example
semodule -i etc/guix-daemon.cil
@end example

Kennzeichnen Sie dann das Dateisystem neu mit @code{restorecon} oder einem
anderen, von Ihrem System angebotenen Mechanismus.

Sobald die Richtlinie installiert ist, das Dateisystem neu gekennzeichnet
wurde und der Daemon neugestartet wurde, sollte er im Kontext
@code{guix_daemon_t} laufen. Sie können dies mit dem folgenden Befehl
nachprüfen:

@example
ps -Zax | grep guix-daemon
@end example

Beobachten Sie die Protokolldateien von SELinux, wenn Sie einen Befehl wie
@code{guix build hello} ausführen, um sich zu überzeugen, dass SELinux alle
notwendigen Operationen gestattet.

@subsubsection Einschränkungen
@cindex SELinux, Einschränkungen

Diese Richtlinie ist nicht perfekt. Im Folgenden finden Sie eine Liste von
Einschränkungen oder merkwürdiger Verhaltensweisen, die bedacht werden
sollten, wenn man die mitgelieferte SELinux-Richtlinie für den Guix-Daemon
einspielt.

@enumerate
@item
@code{guix_daemon_socket_t} wird nicht wirklich benutzt. Keine der
Socket-Operationen benutzt Kontexte, die irgendetwas mit
@code{guix_daemon_socket_t} zu tun haben. Es schadet nicht, diese ungenutzte
Kennzeichnung zu haben, aber es wäre besser, für die Kennzeichnung auch
Socket-Regeln festzulegen.

@item
@code{guix gc} kann nicht auf beliebige Verknüpfungen zu Profilen
zugreifen. Die Kennzeichnung des Ziels einer symbolischen Verknüpfung ist
notwendigerweise unabhängig von der Dateikennzeichnung der
Verknüpfung. Obwohl alle Profile unter $localstatedir gekennzeichnet sind,
erben die Verknüpfungen auf diese Profile die Kennzeichnung desjenigen
Verzeichnisses, in dem sie sich befinden. Für Verknüpfungen im Persönlichen
Ordner des Benutzers ist das @code{user_home_t}, aber Verknüpfungen aus dem
Persönlichen Ordner des Administratornutzers, oder @file{/tmp}, oder das
Arbeitsverzeichnis des HTTP-Servers, etc., funktioniert das
nicht. @code{guix gc} würde es nicht gestattet, diese Verknüpfungen
auszulesen oder zu verfolgen.

@item
Die vom Daemon gebotene Funktionalität, auf TCP-Verbindungen zu lauschen,
könnte nicht mehr funktionieren. Dies könnte zusätzliche Regeln brauchen,
weil SELinux Netzwerk-Sockets anders behandelt als Dateien.

@item
Derzeit wird allen Dateien mit einem Namen, der zum regulären Ausdruck
@code{/gnu/store/.+-(guix-.+|profile)/bin/guix-daemon} passt, die
Kennzeichnung @code{guix_daemon_exec_t} zugewiesen, wodurch @emph{jedee
beliebigee} Datei mit diesem Namen in irgendeinem Profil gestatttet wäre, in
der Domäne @code{guix_daemon_t} ausgeführt zu werden. Das ist nicht
ideal. Ein Angreifer könnte ein Paket erstellen, dass solch eine ausführbare
Datei enthält, und den Nutzer überzeugen, es zu installieren und
auszuführen. Dadurch käme es in die Domäne @code{guix_daemon_t}. Ab diesem
Punkt könnte SELinux nicht mehr verhindern, dass es auf Dateien zugreift,
auf die Prozesse in dieser Domäne zugreifen dürfen.

Wir könnten zum Zeitpunkt der Installation eine wesentlich restriktivere
Richtlinie generieren, für die nur @emph{genau derselbe} Dateiname des
gerade installierten @code{guix-daemon}-Programms als
@code{guix_daemon_exec_t} gekennzeichnet würde, statt einen vieles
umfassenden regulären Ausdruck zu benutzen. Aber dann müsste der
Administratornutzer zum Zeitpunkt der Installation jedes Mal die Richtlinie
installieren oder aktualisieren müssen, sobald das Guix-Paket aktualisiert
wird, dass das tatsächlich in Benutzung befindliche
@code{guix-daemon}-Programm enthält.
@end enumerate

@node Aufruf des guix-daemon
@section Aufruf von @command{guix-daemon}

Das Programm @command{guix-daemon} implementiert alle Funktionalitäten, um
auf den Store zuzugreifen. Dazu gehört das Starten von Erstellungsprozessen,
das Ausführen des Müllsammlers, das Abfragen, ob ein Erstellungsergebnis
verfügbar ist, etc. Normalerweise wird er so als Administratornutzer
(@code{root}) gestartet:

@example
# guix-daemon --build-users-group=guixbuild
@end example

@noindent
Details, wie Sie ihn einrichten, finden Sie im Abschnitt @pxref{Den Daemon einrichten}.

@cindex chroot
@cindex Container, Erstellungsumgebung
@cindex Erstellungsumgebung
@cindex Reproduzierbare Erstellungen
Standardmäßig führt @command{guix-daemon} Erstellungsprozesse mit
unterschiedlichen UIDs aus, die aus der Erstellungsgruppe stammen, deren
Name mit @code{--build-users-group} übergeben wurde. Außerdem läuft jeder
Erstellungsprozess in einer chroot-Umgebung, die nur die Teilmenge des
Stores enthält, von der der Erstellungsprozess abhängt, entsprechend seiner
Ableitung (@pxref{Programmierschnittstelle, derivation}), und ein paar
bestimmte Systemverzeichnisse, darunter standardmäßig auch @file{/dev} und
@file{/dev/pts}. Zudem ist die Erstellungsumgebung auf GNU/Linux ein
@dfn{Container}: Nicht nur hat er seinen eigenen Dateisystembaum, er hat
auch einen separaten Namensraum zum Einhängen von Dateisystemen, seinen
eigenen Namensraum für PIDs, für Netzwerke, etc. Dies hilft dabei,
reproduzierbare Erstellungen zu garantieren (@pxref{Funktionalitäten}).

When the daemon performs a build on behalf of the user, it creates a build
directory under @file{/tmp} or under the directory specified by its
@code{TMPDIR} environment variable; this directory is shared with the
container for the duration of the build.  Be aware that using a directory
other than @file{/tmp} can affect build results---for example, with a longer
directory name, a build process that uses Unix-domain sockets might hit the
name length limitation for @code{sun_path}, which it would otherwise not
hit.

Nach Abschluss der Erstellung wird das Erstellungsverzeichnis automatisch
entfernt, außer wenn die Erstellung fehlgeschlagen ist und der Client
@option{--keep-failed} angegeben hat (@pxref{Aufruf von guix build,
@option{--keep-failed}}).

The daemon listens for connections and spawns one sub-process for each
session started by a client (one of the @command{guix} sub-commands.)  The
@command{guix processes} command allows you to get an overview of the
activity on your system by viewing each of the active sessions and clients.
@xref{Invoking guix processes}, for more information.

Die folgenden Befehlszeilenoptionen werden unterstützt:

@table @code
@item --build-users-group=@var{Gruppe}
Verwende die Benutzerkonten aus der @var{Gruppe}, um Erstellungsprozesse
auszuführen (@pxref{Den Daemon einrichten, build users}).

@item --no-substitutes
@cindex Substitute
Benutze keine Substitute für Erstellungsergebnisse. Das heißt, dass alle
Objekte lokal erstellt werden müssen, und kein Herunterladen von vorab
erstellten Binärdateien erlaubt ist (@pxref{Substitute}).

Wenn der Daemon mit @code{--no-substitutes} ausgeführt wird, können Clients
trotzdem Substitute explizit aktivieren über den entfernten Prozeduraufruf
@code{set-build-options} (@pxref{Der Store}).

@item --substitute-urls=@var{URLs}
@anchor{daemon-substitute-urls}
Benutze @var{URLs} als standardmäßige, leerzeichengetrennte Liste der
Quell-URLs für Substitute. Wenn diese Befehlszeilenoption nicht angegeben
wird, wird @indicateurl{https://mirror.hydra.gnu.org https://hydra.gnu.org}
verwendet (@code{mirror.hydra.gnu.org} ist ein Spiegelserver für
@code{hydra.gnu.org}).

Das hat zur Folge, dass Substitute von den @var{URLs} heruntergeladen werden
können, solange sie mit einer Signatur versehen sind, der vertraut wird
(@pxref{Substitute}).

@cindex Build-Hook
@item --no-build-hook
Den »@dfn{Build-Hook}« nicht benutzen.

»Build-Hook« ist der Name eines Hilfsprogramms, das der Daemon starten kann
und an das er Erstellungsanfragen übermittelt. Durch diesen Mechanismus
können Erstellungen an andere Maschinen ausgelagert werden (@pxref{Auslagern des Daemons einrichten}).

@item --cache-failures
Fehler bei der Erstellung zwischenspeichern. Normalerweise werden nur
erfolgreiche Erstellungen gespeichert.

Wenn diese Befehlszeilenoption benutzt wird, kann @command{guix gc
--list-failures} benutzt werden, um die Menge an Store-Objekten abzufragen,
die als Fehlschläge markiert sind; @command{guix gc --clear-failures}
entfernt Store-Objekte aus der Menge zwischengespeicherter
Fehlschläge. @xref{Aufruf von guix gc}.

@item --cores=@var{n}
@itemx -c @var{n}
@var{n} CPU-Kerne zum Erstellen jeder Ableitung benutzen; @code{0} heißt, so
viele wie verfügbar sind.

Der Vorgabewert ist @code{0}, jeder Client kann jedoch eine abweichende
Anzahl vorgeben, zum Beispiel mit der Befehlszeilenoption @code{--cores} von
@command{guix build} (@pxref{Aufruf von guix build}).

Dadurch wird die Umgebungsvariable @code{NIX_BUILD_CORES} im
Erstellungsprozess definiert, welcher sie benutzen kann, um intern parallele
Ausführungen zuzulassen — zum Beispiel durch Nutzung von @code{make
-j$NIX_BUILD_CORES}.

@item --max-jobs=@var{n}
@itemx -M @var{n}
Höchstenss @var{n} Erstellungsaufträge parallel bearbeiten. Der Vorgabewert
liegt bei @code{1}. Wird er auf @code{0} gesetzt, werden keine Erstellungen
lokal durchgeführt, stattdessen lagert der Daemon sie nur aus (@pxref{Auslagern des Daemons einrichten}) oder sie schlagen einfach fehl.

@item --max-silent-time=@var{Sekunden}
Wenn der Erstellungs- oder Substitutionsprozess länger als
@var{Sekunden}-lang keine Ausgabe erzeugt, wird er abgebrochen und ein
Fehler beim Erstellen gemeldet.

Der Vorgabewert ist @code{0}, was bedeutet, dass es keine Zeitbeschränkung
gibt.

Clients können einen anderen Wert als den hier angegebenen verwenden lassen
(@pxref{Gemeinsame Erstellungsoptionen, @code{--max-silent-time}}).

@item --timeout=@var{Sekunden}
Entsprechend wird hier der Erstellungs- oder Substitutionsprozess
abgebrochen und als Fehlschlag gemeldet, wenn er mehr als
@var{Sekunden}-lang dauert.

Der Vorgabewert ist @code{0}, was bedeutet, dass es keine Zeitbeschränkung
gibt.

Clients können einen anderen Wert verwenden lassen (@pxref{Gemeinsame Erstellungsoptionen, @code{--timeout}}).

@item --rounds=@var{N}
Jede Ableitung @var{n}-mal hintereinander erstellen und einen Fehler melden,
wenn nacheinander ausgewertete Erstellungsergebnisse nicht Bit für Bit
identisch sind. Beachten Sie, dass Clients wie @command{guix build} einen
anderen Wert verwenden lassen können (@pxref{Aufruf von guix build}).

Wenn dies zusammen mit @option{--keep-failed} benutzt wird, bleiben die sich
unterscheidenden Ausgaben im Store unter dem Namen
@file{/gnu/store/@dots{}-check}. Dadurch können Unterschiede zwischen den
beiden Ergebnissen leicht erkannt werden.

@item --debug
Informationen zur Fehlersuche ausgeben.

Dies ist nützlich, um Probleme beim Starten des Daemons nachzuvollziehen;
Clients könn aber auch ein abweichenden Wert verwenden lassen, zum Beispiel
mit der Befehlszeilenoption @code{--verbosity} von @command{guix build}
(@pxref{Aufruf von guix build}).

@item --chroot-directory=@var{Verzeichnis}
Füge das @var{Verzeichnis} zum chroot von Erstellungen hinzu.

Dadurch kann sich das Ergebnis von Erstellungsprozessen ändern — zum
Beispiel, wenn diese optionale Abhängigkeiten aus dem @var{Verzeichnis}
verwenden, wenn sie verfügbar sind, und nicht, wenn es fehlt. Deshalb ist es
nicht empfohlen, dass Sie diese Befehlszeilenoption besser verwenden, besser
sollten Sie dafür sorgen, dass jede Ableitung alle von ihr benötigten
Eingabgen deklariert.

@item --disable-chroot
Erstellungen ohne chroot durchführen.

Diese Befehlszeilenoption zu benutzen, wird nicht empfohlen, denn auch
dadurch bekämen Erstellungsprozesse Zugriff auf nicht deklarierte
Abhängigkeiten. Sie ist allerdings unvermeidlich, wenn @command{guix-daemon}
auf einem Benutzerkonto ohne ausreichende Berechtigungen ausgeführt wird.

@item --log-compression=@var{Typ}
Erstellungsprotokolle werden entsprechend dem @var{Typ} komprimiert, der
entweder @code{gzip}, @code{bzip2} oder @code{none} (für keine Kompression)
sein muss.

Sofern nicht @code{--lose-logs} angegeben wurde, werden alle
Erstellungsprotokolle in der @var{localstatedir} gespeichert. Um Platz zu
sparen, komprimiert sie der Daemon standardmäßig automatisch mit bzip2.

@item --disable-deduplication
@cindex Deduplizieren
Automatische Dateien-»Deduplizierung« im Store ausschalten.

Standardmäßig werden zum Store hinzugefügte Objekte automatisch
»dedupliziert«: Wenn eine neue Datei mit einer anderen im Store
übereinstimmt, wird die neue Datei stattdessen als harte Verknüpfung auf die
andere Datei angelegt. Dies reduziert den Speicherverbrauch auf der Platte
merklich, jedoch steigt andererseits die Auslastung bei der Ein-/Ausgabe im
Erstellungsprozess geringfügig. Durch diese Option wird keine solche
Optimierung durchgeführt.

@item --gc-keep-outputs[=yes|no]
Gibt an, ob der Müllsammler (Garbage Collector, GC) die Ausgaben lebendiger
Ableitungen behalten muss (»yes«) oder nicht (»no«).

@cindex GC-Wurzeln
@cindex Müllsammlerwurzeln
When set to ``yes'', the GC will keep the outputs of any live derivation
available in the store---the @code{.drv} files.  The default is ``no'',
meaning that derivation outputs are kept only if they are reachable from a
GC root.  @xref{Aufruf von guix gc}, for more on GC roots.

@item --gc-keep-derivations[=yes|no]
Gibt an, ob der Müllsammler (GC) Ableitungen behalten muss (»yes«), wenn sie
lebendige Ausgaben haben, oder nicht (»no«).

Für »yes«, den Vorgabewert, behält der Müllsammler Ableitungen —
z.B. @code{.drv}-Dateien —, solange zumindest eine ihrer Ausgaben lebendig
ist. Dadurch können Nutzer den Ursprung der Dateien in ihrem Store
nachvollziehen. Setzt man den Wert auf »no«, wird ein bisschen weniger
Speicher auf der Platte verbraucht.

In this way, setting @code{--gc-keep-derivations} to ``yes'' causes liveness
to flow from outputs to derivations, and setting @code{--gc-keep-outputs} to
``yes'' causes liveness to flow from derivations to outputs.  When both are
set to ``yes'', the effect is to keep all the build prerequisites (the
sources, compiler, libraries, and other build-time tools) of live objects in
the store, regardless of whether these prerequisites are reachable from a GC
root.  This is convenient for developers since it saves rebuilds or
downloads.

@item --impersonate-linux-2.6
Auf Linux-basierten Systemen wird hiermit vorgetäuscht, dass es sich um
Linux 2.6 handeln würde, indem der Kernel für einen
@code{uname}-Systemaufruf als Version der Veröffentlichung mit 2.6
antwortet.

Dies kann hilfreich sein, um Programme zu erstellen, die (normalerweise zu
Unrecht) von der Kernel-Versionsnummer abhängen.

@item --lose-logs
Keine Protokolle der Erstellungen vorhalten. Normalerweise würden solche in
@code{@var{localstatedir}/guix/log} gespeichert.

@item --system=@var{System}
Verwende @var{System} als aktuellen Systemtyp. Standardmäßig ist dies das
Paar aus Befehlssatz und Kernel, welches beim Aufruf von @code{configure}
erkannt wurde, wie zum Beispiel @code{x86_64-linux}.

@item --listen=@var{Endpunkt}
Lausche am @var{Endpunkt} auf Verbindungen. Dabei wird der @var{Endpunkt}
als Dateiname eines Unix-Sockets verstanden, wenn er mit einem @code{/}
(Schrägstrich) beginnt. Andernfalls wird der @var{Endpunkt} als Hostname
oder als Hostname-Port-Paar verstanden, auf dem gelauscht wird. Hier sind
ein paar Beispiele:

@table @code
@item --listen=/gnu/var/daemon
Lausche auf Verbindungen am Unix-Socket @file{/gnu/var/daemon}, falls nötig
wird er dazu erstellt.

@item --listen=localhost
@cindex Daemon, Fernzugriff
@cindex Fernzugriff auf den Daemon
@cindex Daemon, Einrichten auf Clustern
@cindex Cluster, Einrichtung des Daemons
Lausche auf TCP-Verbindungen an der Netzwerkschnittstelle, die
@code{localhost} entspricht, auf Port 44146.

@item --listen=128.0.0.42:1234
Lausche auf TCP-Verbindungen an der Netzwerkschnittstelle, die
@code{128.0.0.42} entspricht, auf Port 1234.
@end table

Diese Befehlszeilenoption kann mehrmals wiederholt werden. In diesem Fall
akzeptiert @command{guix-daemon} Verbindungen auf allen angegebenen
Endpunkten. Benutzer können bei Client-Befehlen angeben, mit welchem
Endpunkt sie sich verbinden möchten, indem sie die Umgebungsvariable
@code{GUIX_DAEMON_SOCKET} festlegen (@pxref{Der Store,
@code{GUIX_DAEMON_SOCKET}}).

@quotation Anmerkung
Das Daemon-Protokoll ist @emph{weder authentifiziert noch
verschlüsselt}. Die Benutzung von @code{--listen=@var{Host}} eignet sich für
lokale Netzwerke, wie z.B. in Rechen-Clustern, wo sich nur solche Knoten mit
dem Daemon verbinden, denen man vertraut. In Situationen, wo ein Fernzugriff
auf den Daemon durchgeführt wird, empfehlen wir, über Unix-Sockets in
Verbindung mit SSH zuzugreifen.
@end quotation

Wird @code{--listen} nicht angegeben, lauscht @command{guix-daemon} auf
Verbindungen auf dem Unix-Socket, der sich unter
@file{@var{localstatedir}/guix/daemon-socket/socket} befindet.
@end table


@node Anwendungen einrichten
@section Anwendungen einrichten

@cindex Fremddistribution
Läuft Guix aufgesetzt auf einer GNU/Linux-Distribution außer GuixSD — einer
sogenannten @dfn{Fremddistribution} —, so sind ein paar zusätzliche Schritte
bei der Einrichtung nötig. Hier finden Sie manche davon.

@subsection Locales

@anchor{locales-and-locpath}
@cindex Locales, nicht auf GuixSD
@vindex LOCPATH
@vindex GUIX_LOCPATH
Über Guix installierte Pakete benutzen nicht die Daten zu Regions- und
Spracheinstellungen (Locales) des Wirtssystems. Stattdessen müssen Sie erst
eines der Locale-Pakete installieren, die für Guix verfügbar sind, und dann
den Wert Ihrer Umgebungsvariablen @code{GUIX_LOCPATH} passend festlegen:

@example
$ guix package -i glibc-locales
$ export GUIX_LOCPATH=$HOME/.guix-profile/lib/locale
@end example

Beachten Sie, dass das Paket @code{glibc-locales} Daten für alle von
GNU@tie{}libc unterstützten Locales enthält und deswegen um die 110@tie{}MiB
wiegt. Alternativ gibt es auch @code{glibc-utf8-locales}, was kleiner, aber
auf ein paar UTF-8-Locales beschränkt ist.

Die Variable @code{GUIX_LOCPATH} spielt eine ähnliche Rolle wie
@code{LOCPATH} (@pxref{Locale Names, @code{LOCPATH},, libc, The GNU C
Library Reference Manual}). Es gibt jedoch zwei wichtige Unterschiede:

@enumerate
@item
@code{GUIX_LOCPATH} wird nur von der libc in Guix beachtet und nicht der von
Fremddistributionen bereitgestellten libc. Mit @code{GUIX_LOCPATH} können
Sie daher sicherstellen, dass die Programme der Fremddistribution keine
inkompatiblen Locale-Daten von Guix laden.

@item
libc hängt an jeden @code{GUIX_LOCPATH}-Eintrag @code{/X.Y} an, wobei
@code{X.Y} die Version von libc ist — z.B. @code{2.22}. Sollte Ihr
Guix-Profil eine Mischung aus Programmen enthalten, die an verschiedene
libc-Versionen gebunden sind, wird jede nur die Locale-Daten im richtigen
Format zu laden versuchen.
@end enumerate

Das ist wichtig, weil das Locale-Datenformat verschiedener libc-Versionen
inkompatibel sein könnte.

@subsection Name Service Switch

@cindex Name Service Switch, glibc
@cindex NSS (Name Service Switch), glibc
@cindex nscd (Name Service Caching Daemon)
@cindex Name Service Caching Daemon (nscd)
Wenn Sie Guix auf einer Fremddistribution verwenden, @emph{empfehlen wir
stärkstens}, dass Sie den @dfn{Name Service Cache Daemon} der
GNU-C-Bibliothek, @command{nscd}, laufen lassen, welcher auf dem Socket
@file{/var/run/nscd/socket} lauschen sollte. Wenn Sie das nicht tun, könnten
mit Guix installierte Anwendungen Probleme beim Auflösen von Hostnamen oder
Benutzerkonten haben, oder sogar abstürzen. Die nächsten Absätze erklären,
warum.

@cindex @file{nsswitch.conf}
Die GNU-C-Bibliothek implementiert einen @dfn{Name Service Switch} (NSS),
welcher einen erweiterbaren Mechanismus zur allgemeinen »Namensauflösung«
darstellt: Hostnamensauflösung, Benutzerkonten und weiteres (@pxref{Name Service Switch,,, libc, The GNU C Library Reference Manual}).

@cindex Network Information Service (NIS)
@cindex NIS (Network Information Service)
Für die Erweiterbarkeit unterstützt der NSS @dfn{Plugins}, welche neue
Implementierungen zur Namensauflösung bieten: Zum Beispiel ermöglicht das
Plugin @code{nss-mdns} die Namensauflösung für @code{.local}-Hostnamen, das
Plugin @code{nis} gestattet die Auflösung von Benutzerkonten über den
Network Information Service (NIS) und so weiter. Diese zusätzlichen
»Auflösungsdienste« werden systemweit konfiguriert in
@file{/etc/nsswitch.conf} und alle auf dem System laufenden Programme halten
sich an diese Einstellungen (@pxref{NSS Configuration File,,, libc, The GNU
C Reference Manual}).

Wenn sie eine Namensauflösung durchführen — zum Beispiel, indem sie die
@code{getaddrinfo}-Funktion in C aufrufen — versuchen die Anwendungen als
Erstes, sich mit dem nscd zu verbinden; ist dies erfolgreich, führt nscd für
sie die weiteren Namensauflösungen durch. Falls nscd nicht läuft, führen sie
selbst die Namensauflösungen durch, indem sie die Namensauflösungsdienste in
ihren eigenen Adressraum laden und ausführen. Diese Namensauflösungsdienste
— die @file{libnss_*.so}-Dateien — werden mit @code{dlopen} geladen, aber
sie kommen von der C-Bibliothek des Wirtssystems und nicht von der
C-Bibliothek, mit der die Anwendung gebunden wurde (also der C-Bibliothek
von Guix).

Und hier kommt es zum Problem: Wenn die Anwendung mit der C-Bibliothek von
Guix (etwa glibc 2.24) gebunden wurde und die NSS-Plugins von einer anderen
C-Bibliothek (etwa @code{libnss_mdns.so} für glibc 2.22) zu laden versucht,
wird sie vermutlich abstürzen oder die Namensauflösungen werden unerwartet
fehlschlagen.

Durch das Ausführen von @command{nscd} auf dem System wird, neben anderen
Vorteilen, dieses Problem der binären Inkompatibilität vermieden, weil diese
@code{libnss_*.so}-Dateien vom @command{nscd}-Prozess geladen werden, nicht
in den Anwendungen selbst.

@subsection X11-Schriftarten

@cindex Schriftarten
Die Mehrheit der graphischen Anwendungen benutzen Fontconfig zum Finden und
Laden von Schriftarten und für die Darstellung im X11-Client. Im Paket
@code{fontconfig} in Guix werden Schriftarten standardmäßig in
@file{$HOME/.guix-profile} gesucht. Um es graphischen Anwendungen, die mit
Guix installiert wurden, zu ermöglichen, Schriftarten anzuzeigen, müssen Sie
die Schriftarten auch mit Guix installieren. Essenzielle Pakete für
Schriftarten sind unter Anderem @code{gs-fonts}, @code{font-dejavu} und
@code{font-gnu-freefont-ttf}.

Um auf Chinesisch, Japanisch oder Koreanisch verfassten Text in graphischen
Anwendungen anzeigen zu können, möchten Sie vielleicht
@code{font-adobe-source-han-sans} oder @code{font-wqy-zenhei}
installieren. Ersteres hat mehrere Ausgaben, für jede Sprachfamilie eine
(@pxref{Pakete mit mehreren Ausgaben.}). Zum Beispiel installiert folgender
Befehl Schriftarten für chinesische Sprachen:

@example
guix package -i font-adobe-source-han-sans:cn
@end example

@cindex @code{xterm}
Ältere Programme wie @command{xterm} benutzen kein Fontconfig, sondern
X-Server-seitige Schriftartendarstellung. Solche Programme setzen voraus,
dass der volle Name einer Schriftart mit XLFD (X Logical Font Description)
angegeben wird, z.B. so:

@example
-*-dejavu sans-medium-r-normal-*-*-100-*-*-*-*-*-1
@end example

Um solche vollen Namen für die in Ihrem Guix-Profil installierten
TrueType-Schriftarten zu verwenden, müssen Sie den Pfad für Schriftarten
(Font Path) des X-Servers anpassen:

@c Note: 'xset' does not accept symlinks so the trick below arranges to
@c get at the real directory.  See <https://bugs.gnu.org/30655>.
@example
xset +fp $(dirname $(readlink -f ~/.guix-profile/share/fonts/truetype/fonts.dir))
@end example

@cindex @code{xlsfonts}
Danach können Sie den Befehl @code{xlsfonts} ausführen (aus dem Paket
@code{xlsfonts}), um sicherzustellen, dass dort Ihre TrueType-Schriftarten
aufgeführt sind.

@cindex @code{fc-cache}
@cindex Font-Cache
Nach der Installation der Schriftarten müssen Sie unter Umständen den
Schriftarten-Zwischenspeicher (Font-Cache) erneuern, um diese in Anwendungen
benutzen zu können. Gleiches gilt, wenn mit Guix installierte Anwendungen
anscheinend keine Schriftarten finden können. Um das Erneuern des
Font-Caches zu erzwingen, führen Sie @code{fc-cache -f} aus. Der Befehl
@code{fc-cache} wird vom Paket @code{fontconfig} angeboten.

@subsection X.509-Zertifikate

@cindex @code{nss-certs}
Das Paket @code{nss-certs} bietet X.509-Zertifikate, womit Programme die
Identität von Web-Servern authentifizieren können, auf die über HTTPS
zugegriffen wird.

Wenn Sie Guix auf einer Fremddistribution verwenden, können Sie dieses Paket
installieren und die relevanten Umgebungsvariablen festlegen, damit Pakete
wissen, wo sie Zertifikate finden. In @xref{X.509-Zertifikate} stehen
genaue Informationen.

@subsection Emacs-Pakete

@cindex @code{emacs}
Wenn Sie mit Guix Pakete für Emacs installieren, werden deren elisp-Dateien
entweder in @file{$HOME/.guix-profile/share/emacs/site-lisp/} oder in
Unterverzeichnissen von
@file{$HOME/.guix-profile/share/emacs/site-lisp/guix.d/}
gespeichert. Letzteres Verzeichnis gibt es, weil es Tausende von
Emacs-Paketen gibt und sie alle im selben Verzeichnis zu speichern
vielleicht nicht verlässlich funktioniert (wegen Namenskonflikten). Daher
halten wir es für richtig, für jedes Paket ein anderes Verzeichnis zu
benutzen. Das Emacs-Paketsystem organisiert die Dateistruktur ähnlich
(@pxref{Package Files,,, emacs, The GNU Emacs Manual}).

Standardmäßig »weiß« Emacs (wenn er mit Guix installiert wurde), wo diese
Pakete liegen, sie müssen also nichts selbst konfigurieren. Wenn Sie aber
aus irgendeinem Grund mit Guix installierte Pakete nicht automatisch laden
lassen möchten, können Sie Emacs mit der Befehlszeilenoption
@code{--no-site-file} starten (@pxref{Init File,,, emacs, The GNU Emacs
Manual}).

@subsection GCC-Toolchain

@cindex GCC
@cindex ld-wrapper

Guix bietet individuelle Compiler-Pakete wie etwa @code{gcc}, aber wenn Sie
einen vollständigen Satz an Werkzeugen zum Kompilieren und Binden von
Quellcode brauchen, werden Sie eigentlich das Paket @code{gcc-toolchain}
haben wollen. Das Paket bietet eine vollständige GCC-Toolchain für die
Entwicklung mit C/C++, einschließlich GCC selbst, der GNU-C-Bibliothek
(Header-Dateien und Binärdateien samt Symbolen zur Fehlersuche/Debugging in
der @code{debug}-Ausgabe), Binutils und einen Wrapper für den Binder/Linker.

@cindex Versuch, unreine Bibliothek zu benutzen, Fehlermeldung

Der Zweck des Wrappers ist, die an den Binder übergebenen
Befehlszeilenoptionen mit @code{-L} und @code{-l} zu überprüfen und jeweils
passende Argumente mit @code{-rpath} anzufügen, womit dann der echte Binder
aufgerufen wird. Standardmäßig weigert sich der Binder-Wrapper, mit
Bibliotheken außerhalb des Stores zu binden, um »Reinheit« zu
gewährleisten. Das kann aber stören, wenn man die Toolchain benutzt, um mit
lokalen Bibliotheken zu binden. Um Referenzen auf Bibliotheken außerhalb des
Stores zu erlauben, müssen Sie die Umgebungsvariable
@code{GUIX_LD_WRAPPER_ALLOW_IMPURITIES} setzen.

@c TODO What else?

@c *********************************************************************
@node Paketverwaltung
@chapter Paketverwaltung

@cindex Pakete
Der Zweck von GNU Guix ist, Benutzern die leichte Installation,
Aktualisierung und Entfernung von Software-Paketen zu ermöglichen, ohne dass
sie ihre Erstellungsprozeduren oder Abhängigkeiten kennen müssen. Guix kann
natürlich noch mehr als diese offensichtlichen Funktionalitäten.

Dieses Kapitel beschreibt die Hauptfunktionalitäten von Guix, sowie die von
Guix angebotenen Paketverwaltungswerkzeuge. Zusätzlich von den im Folgenden
beschriebenen Befehlszeilen-Benutzerschnittstellen (@pxref{Aufruf von guix package, @code{guix package}}) können Sie auch mit der
Emacs-Guix-Schnittstelle (@pxref{Top,,, emacs-guix, The Emacs-Guix Reference
Manual}) arbeiten, nachdem Sie das Paket @code{emacs-guix} installiert haben
(führen Sie zum Einstieg in Emacs-Guix den Emacs-Befehl @kbd{M-x guix-help}
aus):

@example
guix package -i emacs-guix
@end example

@menu
* Funktionalitäten::        Wie Guix Ihr Leben schöner machen wird.
* Aufruf von guix package::  Pakete installieren, entfernen usw.
* Substitute::               Vorerstelle Binärdateien herunterladen.
* Pakete mit mehreren Ausgaben.::  Ein Quellpaket, mehrere Ausgaben.
* Aufruf von guix gc::       Den Müllsammler laufen lassen.
* Aufruf von guix pull::     Das neueste Guix samt Distribution laden.
* Channels::                 Customizing the package collection.
* Inferiors::                Interacting with another revision of Guix.
* Invoking guix describe::   Display information about your Guix revision.
* Aufruf von guix pack::     Software-Bündel erstellen.
* Aufruf von guix archive::  Import und Export von Store-Dateien.
@end menu

@node Funktionalitäten
@section Funktionalitäten

Wenn Sie Guix benutzen, landet jedes Paket schließlich im @dfn{Paket-Store}
in seinem eigenen Verzeichnis — der Name ist ähnlich wie
@file{/gnu/store/xxx-package-1.2}, wobei @code{xxx} eine Zeichenkette in
Base32-Darstellung ist.

Statt diese Verzeichnisse direkt anzugeben, haben Nutzer ihr eigenes
@dfn{Profil}, welches auf diejenigen Pakete zeigt, die sie tatsächlich
benutzen wollen. Diese Profile sind im Persönlichen Ordner des jeweiligen
Nutzers gespeichert als @code{$HOME/.guix-profile}.

Zum Beispiel installiert @code{alice} GCC 4.7.2. Dadurch zeigt dann
@file{/home/alice/.guix-profile/bin/gcc} auf
@file{/gnu/store/@dots{}-gcc-4.7.2/bin/gcc}. Auf demselben Rechner hat
@code{bob} bbereits GCC 4.8.0 installiert. Das Profil von @code{bob} zeigt
dann einfach weiterhin auf @file{/gnu/store/@dots{}-gcc-4.8.0/bin/gcc} —
d.h. beide Versionen von GCC koexistieren auf demselben System, ohne sich zu
stören.

Der Befehl @command{guix package} ist das zentrale Werkzeug, um Pakete zu
verwalten (@pxref{Aufruf von guix package}). Es arbeitet auf dem eigenen
Profil jedes Nutzers und kann @emph{mit normalen Benutzerrechten} ausgeführt
werden.

@cindex Transaktionen
Der Befehl stellt die offensichtlichen Installations-, Entfernungs- und
Aktualisierungsoperationen zur Verfügung. Jeder Aufruf ist tatsächlich eine
eigene @emph{Transaktion}: Entweder die angegebene Operation wird
erfolgreich durchgeführt, oder gar nichts passiert. Wenn also der Prozess
von @command{guix package} während der Transaktion beendet wird, oder es zum
Stromausfall während der Transaktion kommt, dann bleibt der alte, nutzbare
Zustands des Nutzerprofils erhalten.

Zudem kann jede Pakettransaktion @emph{zurückgesetzt} werden
(Rollback). Wenn also zum Beispiel durch eine Aktualisierung eine neue
Version eines Pakets installiert, die einen schwerwiegenden Fehler zur Folge
hat, können Nutzer ihr Profil einfach auf die vorherige Profilinstanz
zurücksetzen, von der sie wissen, dass sie gut lief. Ebenso unterliegt auf
GuixSD auch die globale Systemkonfiguration transaktionellen
Aktualisierungen und Rücksetzungen (@pxref{Das Konfigurationssystems nutzen}).

Alle Pakete im Paket-Store können vom @emph{Müllsammler} (Garbage Collector)
gelöscht werden. Guix ist in der Lage, festzustellen, welche Pakete noch
durch Benutzerprofile referenziert werden, und entfernt nur diese, die
nachweislich nicht mehr referenziert werden (@pxref{Aufruf von guix gc}). Benutzer können auch ausdrücklich alte Generationen ihres Profils
löschen, damit die zugehörigen Pakete vom Müllsammler gelöscht werden
können.

@cindex Reproduzierbarkeit
@cindex Reproduzierbare Erstellungen
Guix takes a @dfn{purely functional} approach to package management, as
described in the introduction (@pxref{Einführung}).  Each
@file{/gnu/store} package directory name contains a hash of all the inputs
that were used to build that package---compiler, libraries, build scripts,
etc.  This direct correspondence allows users to make sure a given package
installation matches the current state of their distribution.  It also helps
maximize @dfn{build reproducibility}: thanks to the isolated build
environments that are used, a given build is likely to yield bit-identical
files when performed on different machines (@pxref{Aufruf des guix-daemon,
container}).

@cindex Substitute
Auf dieser Grundlage kann Guix @dfn{transparent Binär- oder Quelldateien
ausliefern}. Wenn eine vorerstellte Binärdatei für ein
@file{/gnu/store}-Objekt von einer externen Quelle verfügbar ist — ein
@dfn{Substitut} —, lädt Guix sie einfach herunter und entpackt sie,
andernfalls erstellt Guix das Paket lokal aus seinem Quellcode
(@pxref{Substitute}). Weil Erstellungsergebnisse normalerweise Bit für Bit
reproduzierbar sind, müssen die Nutzer den Servern, die Substitute anbieten,
nicht blind vertrauen; sie können eine lokale Erstellung erzwingen und
Substitute @emph{anfechten} (@pxref{Aufruf von guix challenge}).

Kontrolle über die Erstellungsumgebung ist eine auch für Entwickler
nützliche Funktionalität. Der Befehl @command{guix environment} ermöglicht
es Entwicklern eines Pakets, schnell die richtige Entwicklungsumgebung für
ihr Paket einzurichten, ohne manuell die Abhängigkeiten des Pakets in ihr
Profil installieren zu müssen (@pxref{Aufruf von guix environment}).

@cindex replication, of software environments
@cindex provenance tracking, of software artifacts
All of Guix and its package definitions is version-controlled, and
@command{guix pull} allows you to ``travel in time'' on the history of Guix
itself (@pxref{Aufruf von guix pull}).  This makes it possible to replicate a
Guix instance on a different machine or at a later point in time, which in
turn allows you to @emph{replicate complete software environments}, while
retaining precise @dfn{provenance tracking} of the software.

@node Aufruf von guix package
@section Invoking @command{guix package}

@cindex Installieren von Paketen
@cindex Entfernen von Paketen
@cindex Paketinstallation
@cindex Paketentfernung
Der Befehl @command{guix package} ist ein Werkzeug, womit Nutzer Pakete
installieren, aktualisieren, entfernen und auf vorherige Konfigurationen
zurücksetzen können. Dabei wird nur das eigene Profil des Nutzers verwendet,
und es funktioniert mit normalen Benutzerrechten, ohne Administratorrechte
(@pxref{Funktionalitäten}). Die Syntax ist:

@example
guix package @var{Optionen}
@end example
@cindex Transaktionen
In erster Linie geben die @var{Optionen} an, welche Operationen in der
Transaktion durchgeführt werden sollen. Nach Abschluss wird ein neues Profil
erzeugt, aber vorherige @dfn{Generationen} des Profils bleiben verfügbar,
falls der Benutzer auf sie zurückwechseln will.

Um zum Beispiel @code{lua} zu entfernen und @code{guile} und
@code{guile-cairo} in einer einzigen Transaktion zu installieren:

@example
guix package -r lua -i guile guile-cairo
@end example

@command{guix package} unterstützt auch ein @dfn{deklaratives Vorgehen},
wobei der Nutzer die genaue Menge an Paketen, die verfügbar sein sollen,
festlegt und über die Befehlszeilenoption @option{--manifest} übergibt
(@pxref{profile-manifest, @option{--manifest}}).

@cindex Profil
Für jeden Benutzer wird automatisch eine symbolische Verknüpfung zu seinem
Standardprofil angelegt als @file{$HOME/.guix-profile}. Diese symbolische
Verknüpfung zeigt immer auf die aktuelle Generation des Standardprofils des
Benutzers. Somit können Nutzer @file{$HOME/.guix-profile/bin} z.B. zu ihrer
Umgebungsvariablen @code{PATH} hinzufügen.
@cindex Suchpfade
Wenn Sie nicht die Guix System Distribution benutzen, sollten Sie in
Betracht ziehen, folgende Zeilen zu Ihrem @file{~/.bash_profile}
hinzuzufügen (@pxref{Bash Startup Files,,, bash, The GNU Bash Reference
Manual}), damit in neu erzeugten Shells alle Umgebungsvariablen richtig
definiert werden:

@example
GUIX_PROFILE="$HOME/.guix-profile" ; \
source "$HOME/.guix-profile/etc/profile"
@end example

Ist Ihr System für mehrere Nutzer eingerichtet, werden Nutzerprofile an
einem Ort gespeichert, der als @dfn{Müllsammlerwurzel} registriert ist, auf
die @file{$HOME/.guix-profile} zeigt (@pxref{Aufruf von guix gc}). Dieses
Verzeichnis ist normalerweise
@code{@var{localstatedir}/guix/profiles/per-user/@var{Benutzer}}, wobei
@var{localstatedir} der an @code{configure} als @code{--localstatedir}
übergebene Wert ist und @var{Benutzer} für den jeweiligen Benutzernamen
steht. Das @file{per-user}-Verzeichnis wird erstellt, wenn
@command{guix-daemon} gestartet wird, und das Unterverzeichnis
@var{Benutzer} wird durch @command{guix package} erstellt.

Als @var{Optionen} kann vorkommen:

@table @code

@item --install=@var{Paket} @dots{}
@itemx -i @var{Paket} @dots{}
Die angegebenen @var{Paket}e installieren.

Jedes @var{Paket} kann entweder einfach durch seinen Paketnamen aufgeführt
werden, wie @code{guile}, oder als Paketname gefolgt von einem At-Zeichen @@
und einer Versionsnummer, wie @code{guile@@1.8.8} oder auch nur
@code{guile@@1.8} (in letzterem Fall wird die neueste Version mit Präfix
@code{1.8} ausgewählt.)

Wird keine Versionsnummer angegeben, wird die neueste verfügbare Version
ausgewählt. Zudem kann im @var{Paket} ein Doppelpunkt auftauchen, gefolgt
vom Namen einer der Ausgaben des Pakets, wie @code{gcc:doc} oder
@code{binutils@@2.22:lib} (@pxref{Pakete mit mehreren Ausgaben.}). Pakete
mit zugehörigem Namen (und optional der Version) werden unter den Modulen
der GNU-Distribution gesucht (@pxref{Paketmodule}).

@cindex propagierte Eingaben
Manchmal haben Pakete @dfn{propagierte Eingaben}: Als solche werden
Abhängigkeiten bezeichnet, die automatisch zusammen mit dem angeforderten
Paket installiert werden (im Abschnitt @pxref{package-propagated-inputs,
@code{propagated-inputs} in @code{package} objects} sind weitere
Informationen über propagierte Eingaben in Paketdefinitionen zu finden).

@anchor{package-cmd-propagated-inputs}
Ein Beispiel ist die GNU-MPC-Bibliothek: Ihre C-Headerdateien verweisen auf
die der GNU-MPFR-Bibliothek, welche wiederum auf die der GMP-Bibliothek
verweisen. Wenn also MPC installiert wird, werden auch die MPFR- und
GMP-Bibliotheken in das Profil installiert; entfernt man MPC, werden auch
MPFR und GMP entfernt — außer sie wurden noch auf andere Art ausdrücklich
vom Nutzer installiert.

Abgesehen davon setzen Pakete manchmal die Definition von Umgebungsvariablen
für ihre Suchpfade voraus (siehe die Erklärung von @code{--search-paths}
weiter unten). Alle fehlenden oder womöglich falschen Definitionen von
Umgebungsvariablen werden hierbei gemeldet.

@item --install-from-expression=@var{Ausdruck}
@itemx -e @var{Ausdruck}
Das Paket installieren, zu dem der @var{Ausdruck} ausgewertet wird.

Beim @var{Ausdruck} muss es sich um einen Scheme-Ausdruck handeln, der zu
einem @code{<package>}-Objekt ausgewertet wird. Diese Option ist besonders
nützlich, um zwischen gleichnamigen Varianten eines Pakets zu unterscheiden,
durch Ausdrücke wie @code{(@@ (gnu packages base) guile-final)}.

Beachten Sie, dass mit dieser Option die erste Ausgabe des angegebenen
Pakets installiert wird, was unzureichend sein kann, wenn eine bestimmte
Ausgabe eines Pakets mit mehreren Ausgaben gewünscht ist.

@item --install-from-file=@var{Datei}
@itemx -f @var{Datei}
Das Paket installieren, zu dem der Code in der @var{Datei} ausgewertet wird.

Zum Beispiel könnte die @var{Datei} eine Definition wie diese enthalten
(@pxref{Pakete definieren}):

@example
@verbatiminclude package-hello.scm
@end example

Entwickler könnten es für nützlich erachten, eine solche
@file{guix.scm}-Datei im Quellbaum ihres Projekts abzulegen, mit der
Zwischenstände der Entwicklung getestet und reproduzierbare
Erstellungsumgebungen aufgebaut werden können (@pxref{Aufruf von guix environment}).

@item --remove=@var{Paket} @dots{}
@itemx -r @var{Paket} @dots{}
Die angegebenen @var{Paket}e entfernen.

Wie auch bei @code{--install} kann jedes @var{Paket} neben dem Paketnamen
auch eine Versionsnummer und/oder eine Ausgabe benennen. Zum Beispiel würde
@code{-r glibc:debug} die @code{debug}-Ausgabe von @code{glibc} aus dem
Profil entfernen.

@item --upgrade[=@var{Regexp} @dots{}]
@itemx -u [@var{Regexp} @dots{}]
@cindex Pakete aktualisieren
Alle installierten Pakete aktualisieren. Wenn einer oder mehr reguläre
Ausdrücke (Regexps) angegeben wurden, werden nur diejenigen installierten
Pakete aktualisiert, deren Name zu einer der @var{Regexp}s passt. Siehe auch
weiter unten die Befehlszeilenoption @code{--do-not-upgrade}.

Beachten Sie, dass das Paket so auf die neueste Version unter den Paketen
gebracht wird, die in der aktuell installierten Distribution vorliegen. Um
jedoch Ihre Distribution zu aktualisieren, sollten Sie regelmäßig
@command{guix pull} ausführen (@pxref{Aufruf von guix pull}).

@item --do-not-upgrade[=@var{Regexp} @dots{}]
In Verbindung mit der Befehlszeilenoption @code{--upgrade}, führe
@emph{keine} Aktualisierung von Paketen durch, deren Name zum regulären
Ausdruck @var{Regexp} passt. Um zum Beispiel alle Pakete im aktuellen Profil
zu aktualisieren mit Ausnahme derer, die »emacs« im Namen haben:

@example
$ guix package --upgrade . --do-not-upgrade emacs
@end example

@item @anchor{profile-manifest}--manifest=@var{Datei}
@itemx -m @var{Datei}
@cindex Profildeklaration
@cindex Profilmanifest
Erstellt eine neue Generation des Profils aus dem vom Scheme-Code in
@var{Datei} gelieferten Manifest-Objekt.

Dadurch könnrn Sie den Inhalt des Profils @emph{deklarieren}, statt ihn
durch eine Folge von Befehlen wie @code{--install} u.Ä. zu generieren. Der
Vorteil ist, dass die @var{Datei} unter Versionskontrolle gestellt werden
kann, auf andere Maschinen zum Reproduzieren desselben Profils kopiert
werden kann und Ähnliches.

@c FIXME: Add reference to (guix profile) documentation when available.
Der Code in der @var{Datei} muss ein @dfn{Manifest}-Objekt liefern, was
ungefähr einer Liste von Paketen entspricht:

@findex packages->manifest
@example
(use-package-modules guile emacs)

(packages->manifest
 (list emacs
       guile-2.0
       ;; Eine bestimmte Paketausgabe nutzen.
       (list guile-2.0 "debug")))
@end example

@findex specifications->manifest
In diesem Beispiel müssen wir wissen, welche Module die Variablen
@code{emacs} und @code{guile-2.0} definieren, um die richtige Angabe mit
@code{use-package-modules} machen zu können, was umständlich sein kann. Wir
können auch normale Paketnamen angeben und sie durch
@code{specifications->manifest} zu den entsprechenden Paketobjekten
auflösen, zum Beispiel so:

@example
(specifications->manifest
 '("emacs" "guile@@2.2" "guile@@2.2:debug"))
@end example

@item --roll-back
@cindex rücksetzen
@cindex Zurücksetzen von Transaktionen
@cindex Transaktionen, zurücksetzen
Wechselt zur vorherigen @dfn{Generation} des Profils zurück — d.h. mache die
letzte Transaktion rückgängig.

In Verbindung mit Befehlszeilenoptionen wie @code{--install} wird zuerst
zurückgesetzt, bevor andere Aktionen durchgeführt werden.

Ein Rücksetzen der ersten Generation, die installierte Pakete enthält,
wechselt das Profil zur @dfn{nullten Generation}, die keinerlei Dateien
enthält, abgesehen von Metadaten über sich selbst.

Nach dem Zurücksetzen überschreibt das Installieren, Entfernen oder
Aktualisieren von Paketen vormals zukünftige Generationen, d.h. der Verlauf
der Generationen eines Profils ist immer linear.

@item --switch-generation=@var{Muster}
@itemx -S @var{Muster}
@cindex Generationen
Wechselt zu der bestimmten Generation, die durch das @var{Muster} bezeichnet
wird.

Als @var{Muster} kann entweder die Nummer einer Generation oder eine Nummer
mit vorangestelltem »+« oder »-« dienen. Letzteres springt die angegebene
Anzahl an Generationen vor oder zurück. Zum Beispiel kehrt
@code{--switch-generation=+1} nach einem Zurücksetzen wieder zur neueren
Generation zurück.

Der Unterschied zwischen @code{--roll-back} und
@code{--switch-generation=-1} ist, dass @code{--switch-generation} keine
nullte Generation erzeugen wird; existiert die angegebene Generation nicht,
bleibt schlicht die aktuelle Generation erhalten.

@item --search-paths[=@var{Art}]
@cindex Suchpfade
Führe die Definitionen von Umgebungsvariablen auf, in Bash-Syntax, die nötig
sein könnten, um alle installierten Pakete nutzen zu können. Diese
Umgebungsvariablen werden benutzt, um die @dfn{Suchpfade} für Dateien
festzulegen, die von einigen installierten Paketen benutzt werden.

Zum Beispiel braucht GCC die Umgebungsvariablen @code{CPATH} und
@code{LIBRARY_PATH}, um zu wissen, wo sich im Benutzerprofil Header und
Bibliotheken befinden (@pxref{Environment Variables,,, gcc, Using the GNU
Compiler Collection (GCC)}). Wenn GCC und, sagen wir, die C-Bibliothek im
Profil installiert sind, schlägt @code{--search-paths} also vor, diese
Variablen jeweils auf @code{@var{profile}/include} und
@code{@var{profile}/lib} verweisen zu lassen.

Die typische Nutzung ist, in der Shell diese Variablen zu definieren:

@example
$ eval `guix package --search-paths`
@end example

Als @var{Art} kann entweder @code{exact}, @code{prefix} oder @code{suffix}
gewählt werden, wodurch die gelieferten Definitionen der Umgebungsvariablen
entweder exakt die Einstellungen für Guix meldet, oder sie als Präfix oder
Suffix an den aktuellen Wert dieser Variablen anhängt. Gibt man keine
@var{Art} an, wird der Vorgabewert @code{exact} verwendet.

Diese Befehlszeilenoption kann auch benutzt werden, um die
@emph{kombinierten} Suchpfade mehrerer Profile zu berechnen. Betrachten Sie
dieses Beispiel:

@example
$ guix package -p foo -i guile
$ guix package -p bar -i guile-json
$ guix package -p foo -p bar --search-paths
@end example

Der letzte Befehl oben meldet auch die Definition der Umgebungsvariablen
@code{GUILE_LOAD_PATH}, obwohl für sich genommen weder @file{foo} noch
@file{bar} zu dieser Empfehlung führen würden.


@item --profile=@var{Profil}
@itemx -p @var{Profil}
Auf @var{Profil} anstelle des Standardprofils des Benutzers arbeiten.

@cindex Kollisionen, in einem Profil
@cindex Paketkollisionen in Profilen
@cindex Profilkollisionen
@item --allow-collisions
Kollidierende Pakete im neuen Profil zulassen. Benutzung auf eigene Gefahr!

Standardmäßig wird @command{guix package} @dfn{Kollisionen} als Fehler
auffassen und melden. Zu Kollisionen kommt es, wenn zwei oder mehr
verschiedene Versionen oder Varianten desselben Pakets im Profil landen.

@item --verbose
Erzeugt ausführliche Textausgaben. Insbesondere wird auch das
Erstellungsprotokoll der Umgebung auf dem Standard-Fehler-Port (stderr)
ausgegeben.

@item --bootstrap
Erstellt das Profil mit dem Bootstrap-Guile. Diese Option ist nur für
Entwickler der Distribution nützlich.

@end table

Zusätzlich zu diesen Aktionen unterstützt @command{guix package} folgende
Befehlszeilenoptionen, um den momentanen Zustand eines Profils oder die
Verfügbarkeit von Paketen nachzulesen:

@table @option

@item --search=@var{Regexp}
@itemx -s @var{Regexp}
@cindex Suche nach Paketen
Führt alle verfügbaren Pakete aus, deren Name, Zusammenfassung oder
Beschreibung zum regulären Ausdruck @var{Regexp} passt, sortiert nach ihrer
Relevanz. Alle Metadaten passender Pakete werden im @code{recutils}-Format
geliefert (@pxref{Top, GNU recutils databases,, recutils, GNU recutils
manual}).

So können bestimmte Felder mit dem Befehl @command{recsel} extrahiert
werden, zum Beispiel:

@example
$ guix package -s malloc | recsel -p name,version,relevance
name: jemalloc
version: 4.5.0
relevance: 6

name: glibc
version: 2.25
relevance: 1

name: libgc
version: 7.6.0
relevance: 1
@end example

Ebenso kann der Name aller zu den Bedingungen der GNU@tie{}LGPL, Version 3,
verfügbaren Pakete ermittelt werden:

@example
$ guix package -s "" | recsel -p name -e 'license ~ "LGPL 3"'
name: elfutils

name: gmp
@dots{}
@end example

Es ist auch möglich, Suchergebnisse näher einzuschränken, indem Sie
@code{-s} mehrmals übergeben. Zum Beispiel liefert folgender Befehl eines
Liste von Brettspielen:

@example
$ guix package -s '\<board\>' -s game | recsel -p name
name: gnubg
@dots{}
@end example

Würden wir @code{-s game} weglassen, bekämen wir auch Software-Pakete
aufgelistet, die mit »printed circuit boards« (elektronischen Leiterplatten)
zu tun haben; ohne die spitzen Klammern um @code{board} bekämen wir auch
Pakete, die mit »keyboards« (Tastaturen, oder musikalischen Keyboard) zu tun
haben.

Es ist Zeit für ein komplexeres Beispiel. Folgender Befehl sucht
kryptographische Bibliotheken, filtert Haskell-, Perl-, Python- und
Ruby-Bibliotheken heraus und gibt Namen und Zusammenfassung passender Pakete
aus:

@example
$ guix package -s crypto -s library | \
    recsel -e '! (name ~ "^(ghc|perl|python|ruby)")' -p name,synopsis
@end example

@noindent
@xref{Selection Expressions,,, recutils, GNU recutils manual} enthält
weitere Informationen über @dfn{Auswahlausdrücke} mit @code{recsel -e}.

@item --show=@var{Paket}
Zeigt Details über das @var{Paket} aus der Liste verfügbarer Pakete, im
@code{recutils}-Format (@pxref{Top, GNU recutils databases,, recutils, GNU
recutils manual}).

@example
$ guix package --show=python | recsel -p name,version
name: python
version: 2.7.6

name: python
version: 3.3.5
@end example

Sie können auch den vollständigen Namen eines Pakets angeben, um Details nur
über diese Version angezeigt zu bekommen:
@example
$ guix package --show=python@@3.4 | recsel -p name,version
name: python
version: 3.4.3
@end example



@item --list-installed[=@var{Regexp}]
@itemx -I [@var{Regexp}]
Listet die derzeit installierten Pakete im angegebenen Profil auf, die
zuletzt installierten Pakete zuletzt. Wenn ein regulärer Ausdruck
@var{Regexp} angegeben wird, werden nur installierte Pakete aufgeführt,
deren Name zu @var{Regexp} passt.

Zu jedem installierten Paket werden folgende Informationen angezeigt, durch
Tabulatorzeichen getrennt: der Paketname, die Version als Zeichenkette,
welche Teile des Pakets installiert sind (zum Beispiel @code{out}, wenn die
Standard-Paketausgabe installiert ist, @code{include}, wenn seine Header
installiert sind, usw.) und an welchem Pfad das Paket im Store zu finden
ist.

@item --list-available[=@var{Regexp}]
@itemx -A [@var{Regexp}]
Listet Pakete auf, die in der aktuell installierten Distribution dieses
Systems verfügbar sind (@pxref{GNU-Distribution}). Wenn ein regulärer
Ausdruck @var{Regexp} angegeben wird, werden nur Pakete aufgeführt, deren
Name zum regulären Ausdruck @var{Regexp} passt.

Zu jedem Paket werden folgende Informationen getrennt durch Tabulatorzeichen
ausgegeben: der Name, die Version als Zeichenkette, die Teile des Programms
(@pxref{Pakete mit mehreren Ausgaben.}) und die Stelle im Quellcode, an der
das Paket definiert ist.

@item --list-generations[=@var{Muster}]
@itemx -l [@var{Muster}]
@cindex Generationen
Liefert eine Liste der Generationen zusammen mit dem Datum, an dem sie
erzeugt wurden; zu jeder Generation werden zudem die installierten Pakete
angezeigt, zuletzt installierte Pakete zuletzt. Beachten Sie, dass die
nullte Generation niemals angezeigt wird.

Zu jedem installierten Paket werden folgende Informationen durch
Tabulatorzeichen getrennt angezeigt: der Name des Pakets, die Version als
Zeichenkette, welcher Teil des Pakets installiert ist (@pxref{Pakete mit mehreren Ausgaben.}) und an welcher Stelle sich das Paket im Store befindet.

Wenn ein @var{Muster} angegeben wird, liefert der Befehl nur dazu passende
Generationen. Gültige Muster sind zum Beispiel:

@itemize
@item @emph{Ganze Zahlen und kommagetrennte ganze Zahlen}. Beide Muster bezeichnen
Generationsnummern. Zum Beispiel liefert @code{--list-generations=1} die
erste Generation.

Durch @code{--list-generations=1,8,2} werden drei Generationen in der
angegebenen Reihenfolge angezeigt. Weder Leerzeichen noch ein Komma am
Schluss der Liste ist erlaubt.

@item @emph{Bereiche}. @code{--list-generations=2..9} gibt die
angegebenen Generationen und alles dazwischen aus. Beachten Sie, dass der
Bereichsanfang eine kleinere Zahl als das Bereichsende sein muss.

Sie können auch kein Bereichsende angeben, zum Beispiel liefert
@code{--list-generations=2..} alle Generationen ab der zweiten.

@item @emph{Zeitdauern}. Sie können auch die letzten @emph{N}@tie{}Tage, Wochen
or months by passing an integer along with the first letter of the
duration.  For example, @code{--list-generations=20d} lists generations that
are up to 20 days old.
@end itemize

@item --delete-generations[=@var{Muster}]
@itemx -d [@var{Muster}]
Wird kein @var{Muster} angegeben, werden alle Generationen außer der
aktuellen entfernt.

Dieser Befehl akzeptiert dieselben Muster wie
@option{--list-generations}. Wenn ein @var{Muster} angegeben wird, werden
die passenden Generationen gelöscht. Wenn das @var{Muster} für eine
Zeitdauer steht, werden diejenigen Generationen gelöscht, die @emph{älter}
als die angegebene Dauer sind. Zum Beispiel löscht
@code{--delete-generations=1m} die Generationen, die mehr als einen Monat
alt sind.

Falls die aktuelle Generation zum Muster passt, wird sie @emph{nicht}
gelöscht. Auch die nullte Generation wird niemals gelöscht.

Beachten Sie, dass Sie auf gelöschte Generationen nicht zurückwechseln
können. Dieser Befehl sollte also nur mit Vorsicht benutzt werden.

@end table

Zu guter Letzt können Sie, da @command{guix package} Erstellungsprozesse zu
starten vermag, auch alle gemeinsamen Erstellungsoptionen (@pxref{Gemeinsame Erstellungsoptionen}) verwenden. Auch Paketumwandlungsoptionen wie
@option{--with-source} sind möglich (@pxref{Paketumwandlungsoptionen}). Beachten Sie jedoch, dass die verwendeten
Paketumwandlungsoptionen verloren gehen, nachdem Sie die Pakete aktualisiert
haben. Damit Paketumwandlungen über Aktualisierungen hinweg erhalten
bleiben, sollten Sie Ihre eigene Paketvariante in einem Guile-Modul
definieren und zur Umgebungsvariablen @code{GUIX_PACKAGE_PATH} hinzufügen
(@pxref{Pakete definieren}).

@node Substitute
@section Substitute

@cindex Substitute
@cindex vorerstellte Binärdateien
Guix kann transparent Binär- oder Quelldateien ausliefern. Das heißt, Dinge
können sowohl lokal erstellt, als auch als vorerstellte Objekte von einem
Server heruntergeladen werden, oder beides gemischt. Wir bezeichnen diese
vorerstellten Objekte als @dfn{Substitute} — sie substituieren lokale
Erstellungsergebnisse. In vielen Fällen geht das Herunterladen eines
Substituts wesentlich schneller, als Dinge lokal zu erstellen.

Substitute können alles sein, was das Ergebnis einer Ableitungserstellung
ist (@pxref{Ableitungen}). Natürlich sind sie üblicherweise vorerstellte
Paket-Binärdateien, aber wenn zum Beispiel ein Quell-Tarball das Ergebnis
einer Ableitungserstellung ist, kann auch er als Substitut verfügbar sein.

@menu
* Offizieller Substitut-Server::  Eine besondere Quelle von Substituten.
* Substitut-Server autorisieren::  Wie man Substitute an- und abschaltet.
* Substitutauthentifizierung::  Wie Guix Substitute verifiziert.
* Proxy-Einstellungen::      Wie Sie Substitute über einen Proxy beziehen.
* Fehler bei der Substitution::  Was passiert, wenn die Substitution 
                                   fehlschlägt.
* Vom Vertrauen gegenüber Binärdateien::  Wie können Sie diesem binären 
                                              Blob trauen?
@end menu

@node Offizieller Substitut-Server
@subsection Offizieller Substitut-Server

@cindex Hydra
@cindex Build-Farm
Der Server @code{mirror.hydra.gnu.org} ist die Façade für eine offizielle
»Build-Farm«, ein Erstellungswerk, das kontinuierlich Guix-Pakete für einige
Prozessorarchitekturen erstellt und sie als Substitute zur Verfügung
stellt. Dies ist die standardmäßige Quelle von Substituten; durch Übergeben
der Befehlszeilenoption @option{--substitute-urls} an entweder den
@command{guix-daemon} (@pxref{daemon-substitute-urls,, @code{guix-daemon
--substitute-urls}}) oder Client-Werkzeuge wie @command{guix package}
(@pxref{client-substitute-urls,, client @option{--substitute-urls} option})
kann eine abweichende Einstellung benutzt werden.

Substitut-URLs können entweder HTTP oder HTTPS sein. HTTPS wird empfohlen,
weil die Kommunikation verschlüsselt ist; umgekehrt kann bei HTTP die
Kommunikation belauscht werden, wodurch der Angreifer zum Beispiel erfahren
könnte, ob Ihr System über noch nicht behobene Sicherheitsschwachstellen
verfügt.

Substitute von der offiziellen Build-Farm sind standardmäßig erlaubt, wenn
Sie die Guix System Distribution verwenden (@pxref{GNU-Distribution}). Auf
Fremddistributionen sind sie allerdings standardmäßig ausgeschaltet, solange
Sie sie nicht ausdrücklich in einem der empfohlenen Installationsschritte
erlaubt haben (@pxref{Installation}). Die folgenden Absätze beschreiben, wie
Sie Substitute für die offizielle Build-Farm an- oder ausschalten; dieselbe
Prozedur kann auch benutzt werden, um Substitute für einen beliebigen
anderen Substitutsserver zu erlauben.

@node Substitut-Server autorisieren
@subsection Substitut-Server autorisieren

@cindex Sicherheit
@cindex Substitute, deren Autorisierung
@cindex Access Control List (ACL), für Substitute
@cindex ACL (Access Control List), für Substitute
Um es Guix zu gestatten, Substitute von @code{hydra.gnu.org} oder einem
Spiegelserver davon herunterzuladen, müssen Sie den zugehörigen öffentlichen
Schlüssel zur Access Control List (ACL, Zugriffssteuerungsliste) für
Archivimporte hinzufügen, mit Hilfe des Befehls @command{guix archive}
(@pxref{Aufruf von guix archive}). Dies impliziert, dass Sie darauf vertrauen,
dass @code{hydra.gnu.org} nicht kompromittiert wurde und echte Substitute
liefert.

Der öffentliche Schlüssel für @code{hydra.gnu.org} wird zusammen mit Guix
installiert, in das Verzeichnis
@code{@var{prefix}/share/guix/hydra.gnu.org.pub}, wobei @var{prefix} das
Installationspräfix von Guix ist. Wenn Sie Guix aus seinem Quellcode heraus
installieren, stellen Sie sicher, dass Sie die GPG-Signatur von
@file{guix-@value{VERSION}.tar.gz} prüfen, worin sich dieser öffentliche
Schlüssel befindet. Dann können Sie so etwas wie hier ausführen:

@example
# guix archive --authorize < @var{prefix}/share/guix/hydra.gnu.org.pub
@end example

@quotation Anmerkung
Genauso enthält die Datei @file{berlin.guixsd.org.pub} den öffentlichen
Schlüssel für die neue Build-Farm des Guix-Projekts, die unter
@indicateurl{https://berlin.guixsd.org} erreichbar ist.

Derzeit, als dieser Text geschrieben wurde, wird @code{berlin.guixsd.org}
ausgebaut, um besser skalieren zu können, aber Sie könnten es
ausprobieren. Dahinter stecken 20 x86_64-/i686-Erstellungsknoten, die
Substitute früher anbieten könnten als @code{mirror.hydra.gnu.org}.
@end quotation

Sobald es eingerichtet wurde, sollte sich die Ausgabe eines Befehls wie
@code{guix build} von so etwas:

@example
$ guix build emacs --dry-run
The following derivations would be built:
   /gnu/store/yr7bnx8xwcayd6j95r2clmkdl1qh688w-emacs-24.3.drv
   /gnu/store/x8qsh1hlhgjx6cwsjyvybnfv2i37z23w-dbus-1.6.4.tar.gz.drv
   /gnu/store/1ixwp12fl950d15h2cj11c73733jay0z-alsa-lib-1.0.27.1.tar.bz2.drv
   /gnu/store/nlma1pw0p603fpfiqy7kn4zm105r5dmw-util-linux-2.21.drv
@dots{}
@end example

@noindent
in so etwas verwandeln:

@example
$ guix build emacs --dry-run
112.3 MB would be downloaded:
   /gnu/store/pk3n22lbq6ydamyymqkkz7i69wiwjiwi-emacs-24.3
   /gnu/store/2ygn4ncnhrpr61rssa6z0d9x22si0va3-libjpeg-8d
   /gnu/store/71yz6lgx4dazma9dwn2mcjxaah9w77jq-cairo-1.12.16
   /gnu/store/7zdhgp0n1518lvfn8mb96sxqfmvqrl7v-libxrender-0.9.7
@dots{}
@end example

@noindent
Das zeigt an, dass Substitute von @code{hydra.gnu.org} nutzbar sind und für
zukünftige Erstellungen heruntergeladen, wann immer es möglich ist.

@cindex Substitute, wie man sie ausschaltet
Der Substitutsmechanismus kann global ausgeschaltet werden, indem Sie dem
@code{guix-daemon} beim Starten die Befehlszeilenoption
@code{--no-substitutes} übergeben (@pxref{Aufruf des guix-daemon}). Er kann
auch temporär ausgeschaltet werden, indem Sie @code{--no-substitutes} an
@command{guix package}, @command{guix build} und andere
Befehlszeilenwerkzeuge übergeben.

@node Substitutauthentifizierung
@subsection Substitutauthentifizierung

@cindex digitale Signaturen
Guix erkennt, wenn ein verfälschtes Substitut benutzt würde, und meldet
einen Fehler. Ebenso werden Substitute ignoriert, die nich signiert sind,
oder nicht mit einem in der ACL aufgelisteten Schlüssel signiert sind.

Es gibt nur eine Ausnahme: Wenn ein unautorisierter Server Substitute
anbietet, die @emph{Bit für Bit identisch} mit denen von einem
authorisierten Server sind, können sie auch vom unautorisierten Server
heruntergeladen werden. Zum Beispiel, angenommen wir haben zwei
Substitutserver mit dieser Befehlszeilenoption ausgewählt:

@example
--substitute-urls="https://a.example.org https://b.example.org"
@end example

@noindent
@cindex Reproduzierbare Erstellungen
Wenn in der ACL nur der Schlüssel für @code{b.example.org} aufgeführt wurde,
aber @code{a.example.org} @emph{exakt dieselben} Substitute anbietet, wird
Guix auch Substitute von @code{a.example.org} herunterladen, weil es in der
Liste zuerst kommt und als Spiegelserver für @code{b.example.org} aufgefasst
werden kann. In der Praxis haben unabhängige Maschinen bei der Erstellung
normalerweise dieselben Binärdateien als Ergebnis, dank bit-reproduzierbarer
Erstellungen (siehe unten).

Wenn Sie HTTPS benutzen, wird das X.509-Zertifikat des Servers @emph{nicht}
validiert (mit anderen Worten, die Identität des Servers wird nicht
authentifiziert), entgegen dem, was HTTPS-Clients wie Web-Browser
normalerweise tun. Da Guix Substitutinformationen selbst überprüft, wie oben
erklärt, wäre es unnötig (wohingegen mit X.509-Zertifikaten geprüft wird, ob
ein Domain-Name zu öffentlichen Schlüsseln passt).

@node Proxy-Einstellungen
@subsection Proxy-Einstellungen

@vindex http_proxy
Substitute werden über HTTP oder HTTPS heruntergeladen. Die
Umgebungsvariable @code{http_proxy} kann in der Umgebung von
@command{guix-daemon} definiert werden und wirkt sich dann auf das
Herunterladen von Substituten aus. Beachten Sie, dass der Wert von
@code{http_proxy} in der Umgebung, in der @command{guix build},
@command{guix package} und andere Client-Befehle ausgeführt werden,
@emph{keine Rolle spielt}.

@node Fehler bei der Substitution
@subsection Fehler bei der Substitution

Selbst wenn ein Substitut für eine Ableitung verfügbar ist, schlägt die
versuchte Substitution manchmal fehl. Das kann aus vielen Gründen geschehen:
die Substitutsserver könnten offline sein, das Substitut könnte kürzlich
gelöscht worden sein, die Netzwerkverbindunge könnte unterbrochen worden
sein, usw.

Wenn Substitute aktiviert sind und ein Substitut für eine Ableitung zwar
verfügbar ist, aber die versuchte Substitution fehlschlägt, kann Guix
versuchen, die Ableitung lokal zu erstellen, je nachdem, ob
@code{--fallback} übergeben wurde (@pxref{fallback-option,, common build
option @code{--fallback}}). Genauer gesagt, wird keine lokale Erstellung
durchgeführt, solange kein @code{--fallback} angegeben wurde, und die
Ableitung wird als Fehlschlag angesehen. Wenn @code{--fallback} übergeben
wurde, wird Guix versuchen, die Ableitung lokal zu erstellen, und ob die
Ableitung erfolgreich ist oder nicht, hängt davon ab, ob die lokale
Erstellung erfolgreich ist oder nicht. Beachten Sie, dass, falls Substitute
ausgeschaltet oder erst gar kein Substitut verfügbar ist, @emph{immer} eine
lokale Erstellung durchgeführt wird, egal ob @code{--fallback} übergeben
wurde oder nicht.

Um eine Vorstellung zu bekommen, wieviele Substitute gerade verfügbar sind,
können Sie den Befehl @command{guix weather} benutzen (@pxref{Aufruf von guix weather}). Dieser Befehl zeigt Statistiken darüber an, wie es um die von
einem Server verfügbaren Substitute steht.

@node Vom Vertrauen gegenüber Binärdateien
@subsection Vom Vertrauen gegenüber Binärdateien

@cindex Vertrauen, gegenüber vorerstellten Binärdateien
Derzeit hängt die Kontrolle jedes Individuums über seine Rechner von
Institutionen, Unternehmen undsolchen Gruppierungen ab, die über genug Macht
und Entschlusskraft verfügen, die Rechnerinfrastruktur zu sabotieren und
ihre Schwachstellen auszunutzen. Auch wenn es bequem ist, Substitute von
@code{hydra.gnu.org} zu benutzen, ermuntern wir Nutzer, auch selbst
Erstellungen durchzuführen oder gar ihre eigene Build-Farm zu betreiben,
damit @code{hydra.gnu.org} ein weniger interessantes Ziel wird. Eine Art,
uns zu helfen, ist, die von Ihnen erstellte Software mit dem Befehl
@command{guix publish} zu veröffentlichen, damit andere eine größere Auswahl
haben, von welchem Server sie Substitute beziehen möchten (@pxref{Aufruf von guix publish}).

Guix hat die richtigen Grundlagen, um die Reproduzierbarkeit von
Erstellungen zu maximieren (@pxref{Funktionalitäten}). In den meisten Fällen sollten
unabhängige Erstellungen eines bestimmten Pakets zu bitweise identischen
Ergebnissen führen. Wir können also mit Hilfe einer vielschichtigen Menge an
unabhängigen Paketerstellungen die Integrität unseres Systems besser
gewährleisten. Der Befehl @command{guix challenge} hat das Ziel, Nutzern zu
ermöglichen, Substitutserver zu beurteilen, und Entwicklern zu ermöglichen,
nichtdeterministische Paketerstellungen zu finden (@pxref{Aufruf von guix challenge}). Ebenso ermöglicht es die Befehlszeilenoption @option{--check}
von @command{guix build}, dass Nutzer bereits installierte Substitute auf
Echtheit zu prüfen, indem sie lokal nachgebaut werden (@pxref{build-check,
@command{guix build --check}}).

In Zukunft wollen wir, dass Guix Binärdateien an und von Nutzern in einem
Peer-to-Peer veröffentlichen kann. Wenn Sie mit uns dieses Projekt
diskuttieren möchten, kommen Sie auf unsere Mailing-Liste
@email{guix-devel@@gnu.org}.

@node Pakete mit mehreren Ausgaben.
@section Pakete mit mehreren Ausgaben.

@cindex mehrere Ausgaben, bei Paketen
@cindex Paketausgaben
@cindex Ausgaben

Oft haben in Guix definierte Pakete eine einzige @dfn{Ausgabe} — d.h. aus
dem Quellpaket entsteht genau ein Verzeichnis im Store. Wenn Sie
@command{guix package -i glibc} ausführen, wird die Standard-Paketausgabe
des GNU-libc-Pakets installiert; die Standardausgabe wird @code{out}
genannt, aber ihr Name kann weggelassen werden, wie sie an obigem Befehl
sehen. In diesem speziellen Fall enthält die Standard-Paketausgabe von
@code{glibc} alle C-Headerdateien, gemeinsamen Bibliotheken (»Shared
Libraries«), statische Bibliotheken (»Static Libraries«), Dokumentation für
Info sowie andere zusätzliche Dateien.

Manchmal ist es besser, die verschiedenen Arten von Dateien, die aus einem
einzelnen Quellpaket hervorgehen, in getrennte Ausgaben zu unterteilen. Zum
Beispiel installiert die GLib-C-Bibliothek (die von GTK+ und damit
zusammenhängenden Paketen benutzt wird) mehr als 20 MiB an HTML-Seiten mit
Referenzdokumentation. Um den Nutzern, die das nicht brauchen, Platz zu
sparen, wird die Dokumentation in einer separaten Ausgabe abgelegt, genannt
@code{doc}. Um also die Hauptausgabe von GLib zu installieren, zu der alles
außer der Dokumentation gehört, ist der Befehl:

@example
guix package -i glib
@end example

@cindex Dokumentation
Der Befehl, um die Dokumentation zu installieren, ist:

@example
guix package -i glib:doc
@end example

Manche Pakete installieren Programme mit unterschiedlich großem
»Abhängigkeiten-Fußabdruck«. Zum Beispiel installiert das Paket WordNet
sowohl Befehlszeilenwerkzeuge als auch grafische Benutzerschnittstellen
(GUIs). Erstere hängen nur von der C-Bibliothek ab, während Letztere auch
von Tcl/Tk und den zu Grunde liegenden X-Bibliotheken abhängen. Jedenfalls
belassen wir deshalb die Befehlszeilenwerkzeuge in der
Standard-Paketausgabe, während sich die GUIs in einer separaten Ausgabe
befinden. So können Benutzer, die die GUIs nicht brauchen, Platz sparen. Der
Befehl @command{guix size} kann dabei helfen, solche Situationen zu erkennen
(@pxref{Aufruf von guix size}). @command{guix graph} kann auch helfen
(@pxref{Aufruf von guix graph}).

In der GNU-Distribution gibt es viele solche Pakete mit mehreren
Ausgaben. Andere Konventionen für Ausgabenamen sind zum Beispiel @code{lib}
für Bibliotheken und eventuell auch ihre Header-Dateien,, @code{bin} für
eigenständige Programme und @code{debug} für Informationen zur
Fehlerbehandlung (@pxref{Dateien zur Fehlersuche installieren}). Die Ausgaben eines
Pakets stehen in der dritten Spalte der Anzeige von @command{guix package
--list-available} (@pxref{Aufruf von guix package}).


@node Aufruf von guix gc
@section @command{guix gc} aufrufen

@cindex Müllsammler
@cindex Plattenspeicher
Pakete, die zwar installiert sind, aber nicht benutzt werden, können vom
@dfn{Müllsammler} entfernt werden. Mit dem Befehl @command{guix gc} können
Benutzer den Müllsammler ausdrücklich aufrufen, um Speicher im Verzeichnis
@file{/gnu/store} freizugeben. Dies ist der @emph{einzige} Weg, Dateien aus
@file{/gnu/store} zu entfernen — das manuelle Entfernen von Dateien kann den
Store irreparabel beschädigen!

@cindex GC-Wurzeln
@cindex Müllsammlerwurzeln
Der Müllsammler kennt eine Reihe von @dfn{Wurzeln}: Jede Datei in
@file{/gnu/store}, die von einer Wurzel aus erreichbar ist, gilt als
@dfn{lebendig} und kann nicht entfernt werden; jede andere Datei gilt als
@dfn{tot} und ist ein Kandidat, gelöscht zu werden. Die Reihe der
Müllsammlerwurzeln (kurz auch »GC-Wurzeln«, von englisch »Garbage
Collector«) umfasst Standard-Benutzerprofile; standardmäßig werden diese
Müllsammlerwurzeln durch symbolische Verknüpfungen in
@file{/var/guix/gcroots} dargestellt. Neue Müllsammlerwurzeln können zum
Beispiel mit @command{guix build --root} festgelegt werden (@pxref{Aufruf von guix build}).

Bevor Sie mit @code{guix gc --collect-garbage} Speicher freimachen, wollen
Sie vielleicht alte Generationen von Benutzerprofilen löschen, damit alte
Paketerstellungen von diesen Generationen entfernt werden können. Führen Sie
dazu @code{guix package --delete-generations} aus (@pxref{Aufruf von guix package}).

Unsere Empfehlung ist, dass Sie den Müllsammler regelmäßig laufen lassen und
wenn Sie wenig freien Speicherplatz zur Verfügung haben. Um zum Beispiel
sicherzustellen, dass Sie mindestens 5@tie{}GB are auf Ihrer Platte zur
Verfügung haben, benutzen Sie einfach:

@example
guix gc -F 5G
@end example

Es ist völlig sicher, dafür eine nicht interaktive, regelmäßige
Auftragsausführung vorzugeben (@pxref{Geplante Auftragsausführung}, für eine
Erklärung, wie man das in GuixSD tun kann). @command{guix gc} ohne
Befehlszeilenargumente auszuführen, lässt so viel Müll wie möglich sammeln,
aber das ist oft nicht, was man will, denn so muss man unter Umständen
Software erneut erstellen oder erneut herunterladen, weil der Müllsammler
sie als »tot« ansieht, sie aber zur Erstellung anderer Software wiedeer
gebraucht wird — das trifft zum Beispiel auf die Compiler-Toolchain zu.

Der Befehl @command{guix gc} hat drei Arbeitsmodi: Er kann benutzt werden,
um als Müllsammler tote Dateien zu entfernen (das Standardverhalten), um
ganz bestimmte, angegebene Datein zu löschen (mit der Befehlszeilenoption
@code{--delete}), um Müllsammlerinformationen auszugeben oder
fortgeschrittenere Anfragen zu verarbeiten. Die
Müllsammler-Befehlszeilenoptionen sind wie folgt:

@table @code
@item --collect-garbage[=@var{Minimum}]
@itemx -C [@var{Minimum}]
Lässt Müll sammeln — z.B. nicht erreichbare Dateien in @file{/gnu/store} und
seinen Unterverzeichnissen. Wird keine andere Befehlszeilenoption angegeben,
wird standardmäßig diese durchgeführt.

Wenn ein @var{Minimum} angegeben wurde, hört der Müllsammler auf, sobald
@var{Minimum} Bytes gesammelt wurden. Das @var{Minimum} kann die Anzahl der
Bytes bezeichnen oder mit einer Einheit als Suffix versehen sein, wie etwa
@code{MiB} für Mebibytes und @code{GB} für Gigabytes (@pxref{Block size,
size specifications,, coreutils, GNU Coreutils}).

Wird kein @var{Minimum} angegeben, sammelt der Müllsammler allen Müll.

@item --free-space=@var{Menge}
@itemx -F @var{Menge}
Sammelt Müll, bis die angegebene @var{Menge} an freiem Speicher in
@file{/gnu/store} zur Verfügung steht, falls möglich; die @var{Menge} ist
eine Speichergröße wie @code{500MiB}, wie oben beschrieben.

Wenn die angegebene  @var{Menge} oder mehr bereits in @file{/gnu/store} frei
verfügbar ist, passiert nichts.

@item --delete
@itemx -d
Versucht, alle als Argumente angegebenen Dateien oder Verzeichnisse im Store
zu löschen. Dies schlägt fehl, wenn manche der Dateien oder Verzeichnisse
nicht im Store oder noch immer lebendig sind.

@item --list-failures
Store-Objekte auflisten, die zwischengespeicherten Erstellungsfehlern
entsprechen.

Hierbei wird nichts ausgegeben, sofern der Daemon nicht mit
@option{--cache-failures} gestartet wurde (@pxref{Aufruf des guix-daemon,
@option{--cache-failures}}).

@item --clear-failures
Die angegebenen Store-Objekte aus dem Zwischenspeicher für fehlgeschlagene
Erstellungen entfernen.

Auch diese Option macht nur Sinn, wenn der Daemon mit
@option{--cache-failures} gestartet wurde. Andernfalls passiert nichts.

@item --list-dead
Zeigt die Liste toter Dateien und Verzeichnisse an, die sich noch im Store
befinden — das heißt, Dateien, die von keiner Wurzel mehr erreichbar sind.

@item --list-live
Zeige die Liste lebendiger Store-Dateien und -Verzeichnisse.

@end table

Außerdem können Referenzen unter bestehenden Store-Dateien gefunden werden:

@table @code

@item --references
@itemx --referrers
@cindex Paketabhängigkeiten
Listet die referenzierten bzw. sie referenzierenden Objekte der angegebenen
Store-Dateien auf.

@item --requisites
@itemx -R
@cindex Abschluss
Listet alle Voraussetzungen der als Argumente übergebenen Store-Dateien
auf. Voraussetzungen sind die Store-Dateien selbst, ihre Referenzen sowie
die Referenzen davon, rekursiv. Mit anderen Worten, die zurückgelieferte
Liste ist der @dfn{transitive Abschluss} dieser Store-Dateien.

Der Abschnitt @xref{Aufruf von guix size} erklärt ein Werkzeug, um den
Speicherbedarf des Abschlusses eines Elements zu ermitteln. Siehe
@xref{Aufruf von guix graph} für ein Werkzeug, um den Referenzgraph zu
veranschaulichen.

@item --derivers
@cindex Ableitung
Liefert die Ableitung(en), die zu den angegebenen Store-Objekten führen
(@pxref{Ableitungen}).

Zum Beispiel liefert dieser Befehl:

@example
guix gc --derivers `guix package -I ^emacs$ | cut -f4`
@end example

@noindent
die @file{.drv}-Datei(en), die zum in Ihrem Profil installierten
@code{emacs}-Paket führen.

Beachten Sie, dass es auch sein kann, dass keine passenden
@file{.drv}-Dateien existieren, zum Beispiel wenn diese Dateien bereits dem
Müllsammler zum Opfer gefallen sind. Es kann auch passieren, dass es mehr
als eine passende @file{.drv} gibt, bei Ableitungen mit fester Ausgabe.
@end table

Zuletzt können Sie mit folgenden Befehlszeilenoptionen die Integrität des
Stores prüfen und den Plattenspeicherverbrauch im Zaum halten.

@table @option

@item --verify[=@var{Optionen}]
@cindex Integrität, des Stores
@cindex Integritätsprüfung
Die Integrität des Stores verifizieren

Standardmäßig wird sichergestellt, dass alle Store-Objekte, die in der
Datenbank des Daemons als gültig markiert wurden, auch tatsächlich in
@file{/gnu/store} existieren.

Wenn angegeben, müssen die @var{Optionen} eine kommagetrennte Liste aus
mindestens einem der Worte @code{contents} und @code{repair} sein.

Wenn Sie @option{--verify=contents} übergeben, berechnet der Daemon den Hash
des Inhalts jedes Store-Objekts und vergleicht ihn mit dem Hash in der
Datenbank. Sind die Hashes ungleich, wird eine Datenbeschädigung
gemeldet. Weil dabei @emph{alle Dateien im Store} durchlaufen werden, kann
der Befehl viel Zeit brauchen, besonders auf Systemen mit langsamer Platte.

@cindex Store, reparieren
@cindex Datenbeschädigung, Behebung
Mit @option{--verify=repair} oder @option{--verify=contents,repair} versucht
der Daemon, beschädigte Store-Objekte zu reparieren, indem er Substitute für
selbige herunterlädt (@pxref{Substitute}). Weil die Reparatur nicht atomar
und daher womöglich riskant ist, kann nur der Systemadministrator den Befehl
benutzen. Eine weniger aufwendige Alternative, wenn Sie wissen, welches
Objekt beschädigt ist, ist, @command{guix build --repair} zu benutzen
(@pxref{Aufruf von guix build}).

@item --optimize
@cindex Deduplizieren
Den Store durch Nutzung harter Verknüpfungen für identische Dateien
optimieren — mit anderen Worten wird der Store @dfn{dedupliziert}.

Der Daemon führt Deduplizierung automatisch nach jeder erfolgreichen
Erstellung und jedem Importieren eines Archivs durch, sofern er nicht mit
@code{--disable-deduplication} (@pxref{Aufruf des guix-daemon,
@code{--disable-deduplication}}) gestartet wurde. Diese Befehlszeilenoption
brauchen Sie also in erster Linie dann, wenn der Daemon zuvor mit
@code{--disable-deduplication} gestartet worden ist.

@end table

@node Aufruf von guix pull
@section @command{guix pull} aufrufen

@cindex Aktualisieren von Guix
@cindex Updaten von Guix
@cindex @command{guix pull}
@cindex pull
Packages are installed or upgraded to the latest version available in the
distribution currently available on your local machine.  To update that
distribution, along with the Guix tools, you must run @command{guix pull}:
the command downloads the latest Guix source code and package descriptions,
and deploys it.  Source code is downloaded from a @uref{https://git-scm.com,
Git} repository, by default the official GNU@tie{}Guix repository, though
this can be customized.

Danach wird @command{guix package} Pakete und ihre Versionen entsprechend
der gerade heruntergeladenen Kopie von Guix benutzen. Nicht nur das, auch
alle Guix-Befehle und Scheme-Module werden aus der neuesten Version von Guix
kommen. Neue @command{guix}-Unterbefehle, die durch die Aktualisierung
hinzugekommen sind, werden also auch verfügbar.

Jeder Nutzer kann seine Kopie von Guix mittels @command{guix pull}
aktualisieren, wodurch sich nur für den Nutzer etwas verändert, der
@command{guix pull} ausgeführt hat. Wenn also zum Beispiel der
Administratornutzer @code{root} den Befehl @command{guix pull} ausführt, hat
das keine Auswirkungen, auf die für den Benutzer @code{alice} sichtbare
Guix-Version, und umgekehrt.

Das Ergebnis von @command{guix pull} ist ein als
@file{~/.config/guix/current} verfügbares @dfn{Profil} mit dem neuesten
Guix. Stellen Sie sicher, dass es am Anfang Ihres Suchpfades steht, damit
Sie auch wirklich das neueste Guix und sein Info-Handbuch sehen
(@pxref{Dokumentation}):

@example
export PATH="$HOME/.config/guix/current/bin:$PATH"
export INFOPATH="$HOME/.config/guix/current/share/info:$INFOPATH"
@end example

Die Befehlszeilenoption @code{--list-generations} oder kurz @code{-l} listet
ältere von @command{guix pull} erzeugte Generationen auf, zusammen mit
Informationen zu deren Provenienz.

@example
$ guix pull -l
Generation 1	Jun 10 2018 00:18:18
  guix 65956ad
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: origin/master
    commit: 65956ad3526ba09e1f7a40722c96c6ef7c0936fe

Generation 2	Jun 11 2018 11:02:49
  guix e0cc7f6
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: origin/master
    commit: e0cc7f669bec22c37481dd03a7941c7d11a64f1d
  2 new packages: keepalived, libnfnetlink
  6 packages upgraded: emacs-nix-mode@@2.0.4,
    guile2.0-guix@@0.14.0-12.77a1aac, guix@@0.14.0-12.77a1aac,
    heimdal@@7.5.0, milkytracker@@1.02.00, nix@@2.0.4

Generation 3	Jun 13 2018 23:31:07	(current)
  guix 844cc1c
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: origin/master
    commit: 844cc1c8f394f03b404c5bb3aee086922373490c
  28 new packages: emacs-helm-ls-git, emacs-helm-mu, @dots{}
  69 packages upgraded: borg@@1.1.6, cheese@@3.28.0, @dots{}
@end example

@ref{Invoking guix describe, @command{guix describe}}, for other ways to
describe the current status of Guix.

Das Profil @code{~/.config/guix/current} verhält sich genau wie jedes andere
Profil, das von @command{guix package} erzeugt wurde (@pxref{Aufruf von guix package}). Das bedeutet, Sie können seine Generationen auflisten und es auf
die vorherige Generation — also das vorherige Guix — zurücksetzen und so
weiter:

@example
$ guix package -p ~/.config/guix/current --roll-back
switched from generation 3 to 2
$ guix package -p ~/.config/guix/current --delete-generations=1
deleting /var/guix/profiles/per-user/charlie/current-guix-1-link
@end example

Der Befehl @command{guix pull} wird in der Regel ohne Befehlszeilenargumente
aufgerufen, aber er versteht auch folgende Befehlszeilenoptionen:

@table @code
@item --verbose
Ausführliche Informationen ausgeben und Erstellungsprotokolle auf der
Standardfehlerausgabe ausgeben.

@item --url=@var{URL}
@itemx --commit=@var{Commit}
@itemx --branch=@var{Branch}
Download code from the specified @var{url}, at the given @var{commit} (a
valid Git commit ID represented as a hexadecimal string), or @var{branch}.

@cindex @file{channels.scm}, configuration file
@cindex configuration file for channels
These options are provided for convenience, but you can also specify your
configuration in the @file{~/.config/guix/channels.scm} file or using the
@option{--channels} option (see below).

@item --channels=@var{file}
@itemx -C @var{file}
Read the list of channels from @var{file} instead of
@file{~/.config/guix/channels.scm}.  @var{file} must contain Scheme code
that evaluates to a list of channel objects.  @xref{Channels}, for more
information.

@item --list-generations[=@var{Muster}]
@itemx -l [@var{Muster}]
List all the generations of @file{~/.config/guix/current} or, if
@var{pattern} is provided, the subset of generations that match
@var{pattern}.  The syntax of @var{pattern} is the same as with @code{guix
package --list-generations} (@pxref{Aufruf von guix package}).

@ref{Invoking guix describe}, for a way to display information about the
current generation only.

@item --profile=@var{Profil}
@itemx -p @var{Profil}
Use @var{profile} instead of @file{~/.config/guix/current}.

@item --bootstrap
Use the bootstrap Guile to build the latest Guix.  This option is only
useful to Guix developers.
@end table

The @dfn{channel} mechanism allows you to instruct @command{guix pull} which
repository and branch to pull from, as well as @emph{additional}
repositories containing package modules that should be deployed.
@xref{Channels}, for more information.

In addition, @command{guix pull} supports all the common build options
(@pxref{Gemeinsame Erstellungsoptionen}).

@node Channels
@section Channels

@cindex channels
@cindex @file{channels.scm}, configuration file
@cindex configuration file for channels
@cindex @command{guix pull}, configuration file
@cindex configuration of @command{guix pull}
Guix and its package collection are updated by running @command{guix pull}
(@pxref{Aufruf von guix pull}).  By default @command{guix pull} downloads and
deploys Guix itself from the official GNU@tie{}Guix repository.  This can be
customized by defining @dfn{channels} in the
@file{~/.config/guix/channels.scm} file.  A channel specifies a URL and
branch of a Git repository to be deployed, and @command{guix pull} can be
instructed to pull from one or more channels.  In other words, channels can
be used to @emph{customize} and to @emph{extend} Guix, as we will see below.

@subsection Using a Custom Guix Channel

The channel called @code{guix} specifies where Guix itself---its
command-line tools as well as its package collection---should be
downloaded.  For instance, suppose you want to update from your own copy of
the Guix repository at @code{example.org}, and specifically the
@code{super-hacks} branch, you can write in
@code{~/.config/guix/channels.scm} this specification:

@lisp
;; Tell 'guix pull' to use my own repo.
(list (channel
        (name 'guix)
        (url "https://example.org/my-guix.git")
        (branch "super-hacks")))
@end lisp

@noindent
From there on, @command{guix pull} will fetch code from the
@code{super-hacks} branch of the repository at @code{example.org}.

@subsection Specifying Additional Channels

@cindex extending the package collection (channels)
@cindex personal packages (channels)
@cindex channels, for personal packages
You can also specify @emph{additional channels} to pull from.  Let's say you
have a bunch of custom package variants or personal packages that you think
would make little sense to contribute to the Guix project, but would like to
have these packages transparently available to you at the command line.  You
would first write modules containing those package definitions
(@pxref{Paketmodule}), maintain them in a Git repository, and then you
and anyone else can use it as an additional channel to get packages from.
Neat, no?

@c What follows stems from discussions at
@c <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=22629#134> as well as
@c earlier discussions on guix-devel@gnu.org.
@quotation Warning
Before you, dear user, shout---``woow this is @emph{soooo coool}!''---and
publish your personal channel to the world, we would like to share a few
words of caution:

@itemize
@item
Before publishing a channel, please consider contributing your package
definitions to Guix proper (@pxref{Mitwirken}).  Guix as a project is
open to free software of all sorts, and packages in Guix proper are readily
available to all Guix users and benefit from the project's quality assurance
process.

@item
When you maintain package definitions outside Guix, we, Guix developers,
consider that @emph{the compatibility burden is on you}.  Remember that
package modules and package definitions are just Scheme code that uses
various programming interfaces (APIs).  We want to remain free to change
these APIs to keep improving Guix, possibly in ways that break your
channel.  We never change APIs gratuitously, but we will @emph{not} commit
to freezing APIs either.

@item
Corollary: if you're using an external channel and that channel breaks,
please @emph{report the issue to the channel authors}, not to the Guix
project.
@end itemize

You've been warned! Having said this, we believe external channels are a
practical way to exert your freedom to augment Guix' package collection and
to share your improvements, which are basic tenets of
@uref{https://www.gnu.org/philosophy/free-sw.html, free software}.  Please
email us at @email{guix-devel@@gnu.org} if you'd like to discuss this.
@end quotation

Once you have a Git repository containing your own package modules, you can
write @code{~/.config/guix/channels.scm} to instruct @command{guix pull} to
pull from your personal channel @emph{in addition} to the default Guix
channel(s):

@vindex %default-channels
@lisp
;; Add my personal packages to those Guix provides.
(cons (channel
        (name 'my-personal-packages)
        (url "https://example.org/personal-packages.git"))
      %default-channels)
@end lisp

@noindent
Note that the snippet above is (as always!) Scheme code; we use @code{cons}
to add a channel the list of channels that the variable
@code{%default-channels} is bound to (@pxref{Pairs, @code{cons} and lists,,
guile, GNU Guile Reference Manual}).  With this file in place, @command{guix
pull} builds not only Guix but also the package modules from your own
repository.  The result in @file{~/.config/guix/current} is the union of
Guix with your own package modules:

@example
$ guix pull --list-generations
@dots{}
Generation 19	Aug 27 2018 16:20:48
  guix d894ab8
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: d894ab8e9bfabcefa6c49d9ba2e834dd5a73a300
  my-personal-packages dd3df5e
    repository URL: https://example.org/personal-packages.git
    branch: master
    commit: dd3df5e2c8818760a8fc0bd699e55d3b69fef2bb
  11 new packages: my-gimp, my-emacs-with-cool-features, @dots{}
  4 packages upgraded: emacs-racket-mode@@0.0.2-2.1b78827, @dots{}
@end example

@noindent
The output of @command{guix pull} above shows that Generation@tie{}19
includes both Guix and packages from the @code{my-personal-packages}
channel.  Among the new and upgraded packages that are listed, some like
@code{my-gimp} and @code{my-emacs-with-cool-features} might come from
@code{my-personal-packages}, while others come from the Guix default
channel.

@subsection Replicating Guix

@cindex pinning, channels
@cindex replicating Guix
@cindex reproducibility, of Guix
The @command{guix pull --list-generations} output above shows precisely
which commits were used to build this instance of Guix.  We can thus
replicate it, say, on another machine, by providing a channel specification
in @file{~/.config/guix/channels.scm} that is ``pinned'' to these commits:

@lisp
;; Deploy specific commits of my channels of interest.
(list (channel
       (name 'guix)
       (url "https://git.savannah.gnu.org/git/guix.git")
       (commit "d894ab8e9bfabcefa6c49d9ba2e834dd5a73a300"))
      (channel
       (name 'my-personal-packages)
       (url "https://example.org/personal-packages.git")
       (branch "dd3df5e2c8818760a8fc0bd699e55d3b69fef2bb")))
@end lisp

The @command{guix describe --format=channels} command can even generate this
list of channels directly (@pxref{Invoking guix describe}).

At this point the two machines run the @emph{exact same Guix}, with access
to the @emph{exact same packages}.  The output of @command{guix build gimp}
on one machine will be exactly the same, bit for bit, as the output of the
same command on the other machine.  It also means both machines have access
to all the source code of Guix and, transitively, to all the source code of
every package it defines.

This gives you super powers, allowing you to track the provenance of binary
artifacts with very fine grain, and to reproduce software environments at
will---some sort of ``meta reproducibility'' capabilities, if you will.
@xref{Inferiors}, for another way to take advantage of these super powers.

@node Inferiors
@section Inferiors

@c TODO: Remove this once we're more confident about API stability.
@quotation Anmerkung
The functionality described here is a ``technology preview'' as of version
@value{VERSION}.  As such, the interface is subject to change.
@end quotation

@cindex inferiors
@cindex composition of Guix revisions
Sometimes you might need to mix packages from the revision of Guix you're
currently running with packages available in a different revision of Guix.
Guix @dfn{inferiors} allow you to achieve that by composing different Guix
revisions in arbitrary ways.

@cindex inferior packages
Technically, an ``inferior'' is essentially a separate Guix process
connected to your main Guix process through a REPL (@pxref{Invoking guix
repl}).  The @code{(guix inferior)} module allows you to create inferiors
and to communicate with them.  It also provides a high-level interface to
browse and manipulate the packages that an inferior provides---@dfn{inferior
packages}.

When combined with channels (@pxref{Channels}), inferiors provide a simple
way to interact with a separate revision of Guix.  For example, let's assume
you want to install in your profile the current @code{guile} package, along
with the @code{guile-json} as it existed in an older revision of
Guix---perhaps because the newer @code{guile-json} has an incompatible API
and you want to run your code against the old API@.  To do that, you could
write a manifest for use by @code{guix package --manifest} (@pxref{Aufruf von guix package}); in that manifest, you would create an inferior for that old
Guix revision you care about, and you would look up the @code{guile-json}
package in the inferior:

@lisp
(use-modules (guix inferior) (guix channels)
             (srfi srfi-1))   ;for 'first'

(define channels
  ;; This is the old revision from which we want to
  ;; extract guile-json.
  (list (channel
         (name 'guix)
         (url "https://git.savannah.gnu.org/git/guix.git")
         (commit
          "65956ad3526ba09e1f7a40722c96c6ef7c0936fe"))))

(define inferior
  ;; An inferior representing the above revision.
  (inferior-for-channels channels))

;; Now create a manifest with the current "guile" package
;; and the old "guile-json" package.
(packages->manifest
 (list (first (lookup-inferior-packages inferior "guile-json"))
       (specification->package "guile")))
@end lisp

On its first run, @command{guix package --manifest} might have to build the
channel you specified before it can create the inferior; subsequent runs
will be much faster because the Guix revision will be cached.

The @code{(guix inferior)} module provides the following procedures to open
an inferior:

@deffn {Scheme Procedure} inferior-for-channels @var{channels} @
   [#:cache-directory] [#:ttl] Return an inferior for @var{channels}, a list of
channels.  Use the cache at @var{cache-directory}, where entries can be
reclaimed after @var{ttl} seconds.  This procedure opens a new connection to
the build daemon.

As a side effect, this procedure may build or substitute binaries for
@var{channels}, which can take time.
@end deffn

@deffn {Scheme Procedure} open-inferior @var{directory} @
  [#:command "bin/guix"] Open the inferior Guix in @var{directory}, running
@code{@var{directory}/@var{command} repl} or equivalent.  Return @code{#f}
if the inferior could not be launched.
@end deffn

@cindex inferior packages
The procedures listed below allow you to obtain and manipulate inferior
packages.

@deffn {Scheme Procedure} inferior-packages @var{inferior}
Return the list of packages known to @var{inferior}.
@end deffn

@deffn {Scheme Procedure} lookup-inferior-packages @var{inferior} @var{name} @
   [@var{version}] Return the sorted list of inferior packages matching
@var{name} in @var{inferior}, with highest version numbers first.  If
@var{version} is true, return only packages with a version number prefixed
by @var{version}.
@end deffn

@deffn {Scheme Procedure} inferior-package? @var{obj}
Return true if @var{obj} is an inferior package.
@end deffn

@deffn {Scheme Procedure} inferior-package-name @var{package}
@deffnx {Scheme Procedure} inferior-package-version @var{package}
@deffnx {Scheme Procedure} inferior-package-synopsis @var{package}
@deffnx {Scheme Procedure} inferior-package-description @var{package}
@deffnx {Scheme Procedure} inferior-package-home-page @var{package}
@deffnx {Scheme Procedure} inferior-package-location @var{package}
@deffnx {Scheme Procedure} inferior-package-inputs @var{package}
@deffnx {Scheme Procedure} inferior-package-native-inputs @var{package}
@deffnx {Scheme Procedure} inferior-package-propagated-inputs @var{package}
@deffnx {Scheme Procedure} inferior-package-transitive-propagated-inputs @var{package}
@deffnx {Scheme Procedure} inferior-package-native-search-paths @var{package}
@deffnx {Scheme Procedure} inferior-package-transitive-native-search-paths @var{package}
@deffnx {Scheme Procedure} inferior-package-search-paths @var{package}
These procedures are the counterpart of package record accessors
(@pxref{„package“-Referenz}).  Most of them work by querying the inferior
@var{package} comes from, so the inferior must still be live when you call
these procedures.
@end deffn

Inferior packages can be used transparently like any other package or
file-like object in G-expressions (@pxref{G-Ausdrücke}).  They are also
transparently handled by the @code{packages->manifest} procedure, which is
commonly use in manifests (@pxref{Aufruf von guix package, the
@option{--manifest} option of @command{guix package}}).  Thus you can insert
an inferior package pretty much anywhere you would insert a regular package:
in manifests, in the @code{packages} field of your @code{operating-system}
declaration, and so on.

@node Invoking guix describe
@section Invoking @command{guix describe}

@cindex Reproduzierbarkeit
@cindex replicating Guix
Often you may want to answer questions like: ``Which revision of Guix am I
using?'' or ``Which channels am I using?'' This is useful information in
many situations: if you want to @emph{replicate} an environment on a
different machine or user account, if you want to report a bug or to
determine what change in the channels you are using caused it, or if you
want to record your system state for reproducibility purposes.  The
@command{guix describe} command answers these questions.

When run from a @command{guix pull}ed @command{guix}, @command{guix
describe} displays the channel(s) that it was built from, including their
repository URL and commit IDs (@pxref{Channels}):

@example
$ guix describe
Generation 10	Sep 03 2018 17:32:44	(current)
  guix e0fa68c
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: e0fa68c7718fffd33d81af415279d6ddb518f727
@end example

If you're familiar with the Git version control system, this is similar in
spirit to @command{git describe}; the output is also similar to that of
@command{guix pull --list-generations}, but limited to the current
generation (@pxref{Aufruf von guix pull, the @option{--list-generations}
option}).  Because the Git commit ID shown above unambiguously refers to a
snapshot of Guix, this information is all it takes to describe the revision
of Guix you're using, and also to replicate it.

To make it easier to replicate Guix, @command{guix describe} can also be
asked to return a list of channels instead of the human-readable description
above:

@example
$ guix describe -f channels
(list (channel
        (name 'guix)
        (url "https://git.savannah.gnu.org/git/guix.git")
        (commit
          "e0fa68c7718fffd33d81af415279d6ddb518f727")))
@end example

@noindent
You can save this to a file and feed it to @command{guix pull -C} on some
other machine or at a later point in time, which will instantiate @emph{this
exact Guix revision} (@pxref{Aufruf von guix pull, the @option{-C} option}).
From there on, since you're able to deploy the same revision of Guix, you
can just as well @emph{replicate a complete software environment}.  We
humbly think that this is @emph{awesome}, and we hope you'll like it too!

The details of the options supported by @command{guix describe} are as
follows:

@table @code
@item --format=@var{format}
@itemx -f @var{format}
Produce output in the specified @var{format}, one of:

@table @code
@item human
produce human-readable output;
@item channels
produce a list of channel specifications that can be passed to @command{guix
pull -C} or installed as @file{~/.config/guix/channels.scm} (@pxref{Aufruf von guix pull}).
@end table
@end table

@node Aufruf von guix pack
@section Invoking @command{guix pack}

Occasionally you want to pass software to people who are not (yet!)  lucky
enough to be using Guix.  You'd tell them to run @command{guix package -i
@var{something}}, but that's not possible in this case.  This is where
@command{guix pack} comes in.

@quotation Anmerkung
If you are looking for ways to exchange binaries among machines that already
run Guix, @pxref{Aufruf von guix copy}, @ref{Aufruf von guix publish}, and
@ref{Aufruf von guix archive}.
@end quotation

@cindex pack
@cindex bundle
@cindex application bundle
@cindex software bundle
The @command{guix pack} command creates a shrink-wrapped @dfn{pack} or
@dfn{software bundle}: it creates a tarball or some other archive containing
the binaries of the software you're interested in, and all its
dependencies.  The resulting archive can be used on any machine that does
not have Guix, and people can run the exact same binaries as those you have
with Guix.  The pack itself is created in a bit-reproducible fashion, so
anyone can verify that it really contains the build results that you pretend
to be shipping.

For example, to create a bundle containing Guile, Emacs, Geiser, and all
their dependencies, you can run:

@example
$ guix pack guile emacs geiser
@dots{}
/gnu/store/@dots{}-pack.tar.gz
@end example

The result here is a tarball containing a @file{/gnu/store} directory with
all the relevant packages.  The resulting tarball contains a @dfn{profile}
with the three packages of interest; the profile is the same as would be
created by @command{guix package -i}.  It is this mechanism that is used to
create Guix's own standalone binary tarball (@pxref{Aus Binärdatei installieren}).

Users of this pack would have to run
@file{/gnu/store/@dots{}-profile/bin/guile} to run Guile, which you may find
inconvenient.  To work around it, you can create, say, a @file{/opt/gnu/bin}
symlink to the profile:

@example
guix pack -S /opt/gnu/bin=bin guile emacs geiser
@end example

@noindent
That way, users can happily type @file{/opt/gnu/bin/guile} and enjoy.

@cindex relocatable binaries, with @command{guix pack}
What if the recipient of your pack does not have root privileges on their
machine, and thus cannot unpack it in the root file system? In that case,
you will want to use the @code{--relocatable} option (see below).  This
option produces @dfn{relocatable binaries}, meaning they they can be placed
anywhere in the file system hierarchy: in the example above, users can
unpack your tarball in their home directory and directly run
@file{./opt/gnu/bin/guile}.

@cindex Docker, build an image with guix pack
Alternatively, you can produce a pack in the Docker image format using the
following command:

@example
guix pack -f docker guile emacs geiser
@end example

@noindent
The result is a tarball that can be passed to the @command{docker load}
command.  See the
@uref{https://docs.docker.com/engine/reference/commandline/load/, Docker
documentation} for more information.

@cindex Singularity, build an image with guix pack
@cindex SquashFS, build an image with guix pack
Yet another option is to produce a SquashFS image with the following
command:

@example
guix pack -f squashfs guile emacs geiser
@end example

@noindent
The result is a SquashFS file system image that can either be mounted or
directly be used as a file system container image with the
@uref{http://singularity.lbl.gov, Singularity container execution
environment}, using commands like @command{singularity shell} or
@command{singularity exec}.

Several command-line options allow you to customize your pack:

@table @code
@item --format=@var{format}
@itemx -f @var{format}
Produce a pack in the given @var{format}.

The available formats are:

@table @code
@item tarball
This is the default format.  It produces a tarball containing all the
specified binaries and symlinks.

@item docker
This produces a tarball that follows the
@uref{https://github.com/docker/docker/blob/master/image/spec/v1.2.md,
Docker Image Specification}.

@item squashfs
This produces a SquashFS image containing all the specified binaries and
symlinks, as well as empty mount points for virtual file systems like
procfs.
@end table

@item --relocatable
@itemx -R
Produce @dfn{relocatable binaries}---i.e., binaries that can be placed
anywhere in the file system hierarchy and run from there.  For example, if
you create a pack containing Bash with:

@example
guix pack -R -S /mybin=bin bash
@end example

@noindent
... you can copy that pack to a machine that lacks Guix, and from your home
directory as a normal user, run:

@example
tar xf pack.tar.gz
./mybin/sh
@end example

@noindent
In that shell, if you type @code{ls /gnu/store}, you'll notice that
@file{/gnu/store} shows up and contains all the dependencies of @code{bash},
even though the machine actually lacks @file{/gnu/store} altogether! That is
probably the simplest way to deploy Guix-built software on a non-Guix
machine.

There's a gotcha though: this technique relies on the @dfn{user namespace}
feature of the kernel Linux, which allows unprivileged users to mount or
change root.  Old versions of Linux did not support it, and some GNU/Linux
distributions turn it off; on these systems, programs from the pack
@emph{will fail to run}, unless they are unpacked in the root file system.

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This has the same purpose as the same-named option in @command{guix build}
(@pxref{Zusätzliche Erstellungsoptionen, @code{--expression} in @command{guix
build}}).

@item --manifest=@var{Datei}
@itemx -m @var{Datei}
Use the packages contained in the manifest object returned by the Scheme
code in @var{file}.

This has a similar purpose as the same-named option in @command{guix
package} (@pxref{profile-manifest, @option{--manifest}}) and uses the same
manifest files.  It allows you to define a collection of packages once and
use it both for creating profiles and for creating archives for use on
machines that do not have Guix installed.  Note that you can specify
@emph{either} a manifest file @emph{or} a list of packages, but not both.

@item --system=@var{System}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of the
system type of the build host.

@item --target=@var{triplet}
@cindex cross-compilation
Cross-build for @var{triplet}, which must be a valid GNU triplet, such as
@code{"mips64el-linux-gnu"} (@pxref{Specifying target triplets, GNU
configuration triplets,, autoconf, Autoconf}).

@item --compression=@var{tool}
@itemx -C @var{tool}
Compress the resulting tarball using @var{tool}---one of @code{gzip},
@code{bzip2}, @code{xz}, @code{lzip}, or @code{none} for no compression.

@item --symlink=@var{spec}
@itemx -S @var{spec}
Add the symlinks specified by @var{spec} to the pack.  This option can
appear several times.

@var{spec} has the form @code{@var{source}=@var{target}}, where @var{source}
is the symlink that will be created and @var{target} is the symlink target.

For instance, @code{-S /opt/gnu/bin=bin} creates a @file{/opt/gnu/bin}
symlink pointing to the @file{bin} sub-directory of the profile.

@item --localstatedir
Include the ``local state directory'', @file{/var/guix}, in the resulting
pack.

@file{/var/guix} contains the store database (@pxref{Der Store}) as well as
garbage-collector roots (@pxref{Aufruf von guix gc}).  Providing it in the
pack means that the store is ``complete'' and manageable by Guix; not
providing it pack means that the store is ``dead'': items cannot be added to
it or removed from it after extraction of the pack.

One use case for this is the Guix self-contained binary tarball
(@pxref{Aus Binärdatei installieren}).

@item --bootstrap
Use the bootstrap binaries to build the pack.  This option is only useful to
Guix developers.
@end table

In addition, @command{guix pack} supports all the common build options
(@pxref{Gemeinsame Erstellungsoptionen}) and all the package transformation options
(@pxref{Paketumwandlungsoptionen}).


@node Aufruf von guix archive
@section Invoking @command{guix archive}

@cindex @command{guix archive}
@cindex archive
The @command{guix archive} command allows users to @dfn{export} files from
the store into a single archive, and to later @dfn{import} them on a machine
that runs Guix.  In particular, it allows store files to be transferred from
one machine to the store on another machine.

@quotation Anmerkung
If you're looking for a way to produce archives in a format suitable for
tools other than Guix, @pxref{Aufruf von guix pack}.
@end quotation

@cindex exporting store items
To export store files as an archive to standard output, run:

@example
guix archive --export @var{options} @var{specifications}...
@end example

@var{specifications} may be either store file names or package
specifications, as for @command{guix package} (@pxref{Aufruf von guix package}).  For instance, the following command creates an archive
containing the @code{gui} output of the @code{git} package and the main
output of @code{emacs}:

@example
guix archive --export git:gui /gnu/store/...-emacs-24.3 > great.nar
@end example

If the specified packages are not built yet, @command{guix archive}
automatically builds them.  The build process may be controlled with the
common build options (@pxref{Gemeinsame Erstellungsoptionen}).

To transfer the @code{emacs} package to a machine connected over SSH, one
would run:

@example
guix archive --export -r emacs | ssh the-machine guix archive --import
@end example

@noindent
Similarly, a complete user profile may be transferred from one machine to
another like this:

@example
guix archive --export -r $(readlink -f ~/.guix-profile) | \
  ssh the-machine guix-archive --import
@end example

@noindent
However, note that, in both examples, all of @code{emacs} and the profile as
well as all of their dependencies are transferred (due to @code{-r}),
regardless of what is already available in the store on the target machine.
The @code{--missing} option can help figure out which items are missing from
the target store.  The @command{guix copy} command simplifies and optimizes
this whole process, so this is probably what you should use in this case
(@pxref{Aufruf von guix copy}).

@cindex nar, archive format
@cindex normalized archive (nar)
Archives are stored in the ``normalized archive'' or ``nar'' format, which
is comparable in spirit to `tar', but with differences that make it more
appropriate for our purposes.  First, rather than recording all Unix
metadata for each file, the nar format only mentions the file type (regular,
directory, or symbolic link); Unix permissions and owner/group are
dismissed.  Second, the order in which directory entries are stored always
follows the order of file names according to the C locale collation order.
This makes archive production fully deterministic.

@c FIXME: Add xref to daemon doc about signatures.
When exporting, the daemon digitally signs the contents of the archive, and
that digital signature is appended.  When importing, the daemon verifies the
signature and rejects the import in case of an invalid signature or if the
signing key is not authorized.

The main options are:

@table @code
@item --export
Export the specified store files or packages (see below.)  Write the
resulting archive to the standard output.

Dependencies are @emph{not} included in the output, unless
@code{--recursive} is passed.

@item -r
@itemx --recursive
When combined with @code{--export}, this instructs @command{guix archive} to
include dependencies of the given items in the archive.  Thus, the resulting
archive is self-contained: it contains the closure of the exported store
items.

@item --import
Read an archive from the standard input, and import the files listed therein
into the store.  Abort if the archive has an invalid digital signature, or
if it is signed by a public key not among the authorized keys (see
@code{--authorize} below.)

@item --missing
Read a list of store file names from the standard input, one per line, and
write on the standard output the subset of these files missing from the
store.

@item --generate-key[=@var{parameters}]
@cindex signing, archives
Generate a new key pair for the daemon.  This is a prerequisite before
archives can be exported with @code{--export}.  Note that this operation
usually takes time, because it needs to gather enough entropy to generate
the key pair.

The generated key pair is typically stored under @file{/etc/guix}, in
@file{signing-key.pub} (public key) and @file{signing-key.sec} (private key,
which must be kept secret.)  When @var{parameters} is omitted, an ECDSA key
using the Ed25519 curve is generated, or, for Libgcrypt versions before
1.6.0, it is a 4096-bit RSA key.  Alternatively, @var{parameters} can
specify @code{genkey} parameters suitable for Libgcrypt (@pxref{General
public-key related Functions, @code{gcry_pk_genkey},, gcrypt, The Libgcrypt
Reference Manual}).

@item --authorize
@cindex authorizing, archives
Authorize imports signed by the public key passed on standard input.  The
public key must be in ``s-expression advanced format''---i.e., the same
format as the @file{signing-key.pub} file.

The list of authorized keys is kept in the human-editable file
@file{/etc/guix/acl}.  The file contains
@url{http://people.csail.mit.edu/rivest/Sexp.txt, ``advanced-format
s-expressions''} and is structured as an access-control list in the
@url{http://theworld.com/~cme/spki.txt, Simple Public-Key Infrastructure
(SPKI)}.

@item --extract=@var{directory}
@itemx -x @var{directory}
Read a single-item archive as served by substitute servers
(@pxref{Substitute}) and extract it to @var{directory}.  This is a
low-level operation needed in only very narrow use cases; see below.

For example, the following command extracts the substitute for Emacs served
by @code{hydra.gnu.org} to @file{/tmp/emacs}:

@example
$ wget -O - \
  https://hydra.gnu.org/nar/@dots{}-emacs-24.5 \
  | bunzip2 | guix archive -x /tmp/emacs
@end example

Single-item archives are different from multiple-item archives produced by
@command{guix archive --export}; they contain a single store item, and they
do @emph{not} embed a signature.  Thus this operation does @emph{no}
signature verification and its output should be considered unsafe.

The primary purpose of this operation is to facilitate inspection of archive
contents coming from possibly untrusted substitute servers.

@end table

@c *********************************************************************
@node Programmierschnittstelle
@chapter Programmierschnittstelle

GNU Guix provides several Scheme programming interfaces (APIs) to define,
build, and query packages.  The first interface allows users to write
high-level package definitions.  These definitions refer to familiar
packaging concepts, such as the name and version of a package, its build
system, and its dependencies.  These definitions can then be turned into
concrete build actions.

Build actions are performed by the Guix daemon, on behalf of users.  In a
standard setup, the daemon has write access to the store---the
@file{/gnu/store} directory---whereas users do not.  The recommended setup
also has the daemon perform builds in chroots, under a specific build users,
to minimize interference with the rest of the system.

@cindex Ableitung
Lower-level APIs are available to interact with the daemon and the store.
To instruct the daemon to perform a build action, users actually provide it
with a @dfn{derivation}.  A derivation is a low-level representation of the
build actions to be taken, and the environment in which they should
occur---derivations are to package definitions what assembly is to C
programs.  The term ``derivation'' comes from the fact that build results
@emph{derive} from them.

This chapter describes all these APIs in turn, starting from high-level
package definitions.

@menu
* Pakete definieren::        Wie Sie neue Pakete definieren.
* Erstellungssysteme::       Angeben, wie Pakete erstellt werden.
* Der Store::                Den Paket-Store verändern.
* Ableitungen::              Systemnahe Schnittstelle für Paketableitungen.
* Die Store-Monade::         Rein funktionale Schnittstelle zum Store.
* G-Ausdrücke::             Erstellungsausdrücke verarbeiten.
* Invoking guix repl::       Fiddling with Guix interactively.
@end menu

@node Pakete definieren
@section Pakete definieren

The high-level interface to package definitions is implemented in the
@code{(guix packages)} and @code{(guix build-system)} modules.  As an
example, the package definition, or @dfn{recipe}, for the GNU Hello package
looks like this:

@example
(define-module (gnu packages hello)
  #:use-module (guix packages)
  #:use-module (guix download)
  #:use-module (guix build-system gnu)
  #:use-module (guix licenses)
  #:use-module (gnu packages gawk))

(define-public hello
  (package
    (name "hello")
    (version "2.10")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnu/hello/hello-" version
                                  ".tar.gz"))
              (sha256
               (base32
                "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
    (build-system gnu-build-system)
    (arguments '(#:configure-flags '("--enable-silent-rules")))
    (inputs `(("gawk" ,gawk)))
    (synopsis "Hello, GNU world: An example GNU package")
    (description "Guess what GNU Hello prints!")
    (home-page "http://www.gnu.org/software/hello/")
    (license gpl3+)))
@end example

@noindent
Without being a Scheme expert, the reader may have guessed the meaning of
the various fields here.  This expression binds the variable @code{hello} to
a @code{<package>} object, which is essentially a record (@pxref{SRFI-9,
Scheme records,, guile, GNU Guile Reference Manual}).  This package object
can be inspected using procedures found in the @code{(guix packages)}
module; for instance, @code{(package-name hello)}
returns---surprise!---@code{"hello"}.

With luck, you may be able to import part or all of the definition of the
package you are interested in from another repository, using the @code{guix
import} command (@pxref{Aufruf von guix import}).

In the example above, @var{hello} is defined in a module of its own,
@code{(gnu packages hello)}.  Technically, this is not strictly necessary,
but it is convenient to do so: all the packages defined in modules under
@code{(gnu packages @dots{})} are automatically known to the command-line
tools (@pxref{Paketmodule}).

There are a few points worth noting in the above package definition:

@itemize
@item
The @code{source} field of the package is an @code{<origin>} object
(@pxref{„origin“-Referenz}, for the complete reference).  Here, the
@code{url-fetch} method from @code{(guix download)} is used, meaning that
the source is a file to be downloaded over FTP or HTTP.

The @code{mirror://gnu} prefix instructs @code{url-fetch} to use one of the
GNU mirrors defined in @code{(guix download)}.

The @code{sha256} field specifies the expected SHA256 hash of the file being
downloaded.  It is mandatory, and allows Guix to check the integrity of the
file.  The @code{(base32 @dots{})} form introduces the base32 representation
of the hash.  You can obtain this information with @code{guix download}
(@pxref{Aufruf von guix download}) and @code{guix hash} (@pxref{Aufruf von guix hash}).

@cindex patches
When needed, the @code{origin} form can also have a @code{patches} field
listing patches to be applied, and a @code{snippet} field giving a Scheme
expression to modify the source code.

@item
@cindex GNU-Erstellungssystem
The @code{build-system} field specifies the procedure to build the package
(@pxref{Erstellungssysteme}).  Here, @var{gnu-build-system} represents the
familiar GNU Build System, where packages may be configured, built, and
installed with the usual @code{./configure && make && make check && make
install} command sequence.

@item
The @code{arguments} field specifies options for the build system
(@pxref{Erstellungssysteme}).  Here it is interpreted by @var{gnu-build-system}
as a request run @file{configure} with the @code{--enable-silent-rules}
flag.

@cindex quote
@cindex quoting
@findex '
@findex quote
What about these quote (@code{'}) characters? They are Scheme syntax to
introduce a literal list; @code{'} is synonymous with @code{quote}.
@xref{Expression Syntax, quoting,, guile, GNU Guile Reference Manual}, for
details.  Here the value of the @code{arguments} field is a list of
arguments passed to the build system down the road, as with @code{apply}
(@pxref{Fly Evaluation, @code{apply},, guile, GNU Guile Reference Manual}).

The hash-colon (@code{#:}) sequence defines a Scheme @dfn{keyword}
(@pxref{Keywords,,, guile, GNU Guile Reference Manual}), and
@code{#:configure-flags} is a keyword used to pass a keyword argument to the
build system (@pxref{Coding With Keywords,,, guile, GNU Guile Reference
Manual}).

@item
The @code{inputs} field specifies inputs to the build process---i.e.,
build-time or run-time dependencies of the package.  Here, we define an
input called @code{"gawk"} whose value is that of the @var{gawk} variable;
@var{gawk} is itself bound to a @code{<package>} object.

@cindex backquote (quasiquote)
@findex `
@findex quasiquote
@cindex comma (unquote)
@findex ,
@findex unquote
@findex ,@@
@findex unquote-splicing
Again, @code{`} (a backquote, synonymous with @code{quasiquote}) allows us
to introduce a literal list in the @code{inputs} field, while @code{,} (a
comma, synonymous with @code{unquote}) allows us to insert a value in that
list (@pxref{Expression Syntax, unquote,, guile, GNU Guile Reference
Manual}).

Note that GCC, Coreutils, Bash, and other essential tools do not need to be
specified as inputs here.  Instead, @var{gnu-build-system} takes care of
ensuring that they are present (@pxref{Erstellungssysteme}).

However, any other dependencies need to be specified in the @code{inputs}
field.  Any dependency not specified here will simply be unavailable to the
build process, possibly leading to a build failure.
@end itemize

@xref{„package“-Referenz}, for a full description of possible fields.

Once a package definition is in place, the package may actually be built
using the @code{guix build} command-line tool (@pxref{Aufruf von guix build}),
troubleshooting any build failures you encounter (@pxref{Fehlschläge beim Erstellen untersuchen}).  You can easily jump back to the package definition using the
@command{guix edit} command (@pxref{Aufruf von guix edit}).  @xref{Paketrichtlinien}, for more information on how to test package definitions, and
@ref{Aufruf von guix lint}, for information on how to check a definition for
style conformance.
@vindex GUIX_PACKAGE_PATH
Lastly, @pxref{Channels}, for information on how to extend the distribution
by adding your own package definitions in a ``channel''.

Finally, updating the package definition to a new upstream version can be
partly automated by the @command{guix refresh} command (@pxref{Aufruf von guix refresh}).

Behind the scenes, a derivation corresponding to the @code{<package>} object
is first computed by the @code{package-derivation} procedure.  That
derivation is stored in a @code{.drv} file under @file{/gnu/store}.  The
build actions it prescribes may then be realized by using the
@code{build-derivations} procedure (@pxref{Der Store}).

@deffn {Scheme Procedure} package-derivation @var{store} @var{package} [@var{system}]
Return the @code{<derivation>} object of @var{package} for @var{system}
(@pxref{Ableitungen}).

@var{package} must be a valid @code{<package>} object, and @var{system} must
be a string denoting the target system type---e.g., @code{"x86_64-linux"}
for an x86_64 Linux-based GNU system.  @var{store} must be a connection to
the daemon, which operates on the store (@pxref{Der Store}).
@end deffn

@noindent
@cindex cross-compilation
Similarly, it is possible to compute a derivation that cross-builds a
package for some other system:

@deffn {Scheme Procedure} package-cross-derivation @var{store} @
            @var{package} @var{target} [@var{system}] Return the @code{<derivation>}
object of @var{package} cross-built from @var{system} to @var{target}.

@var{target} must be a valid GNU triplet denoting the target hardware and
operating system, such as @code{"mips64el-linux-gnu"} (@pxref{Configuration
Names, GNU configuration triplets,, configure, GNU Configure and Build
System}).
@end deffn

@cindex package transformations
@cindex input rewriting
@cindex dependency tree rewriting
Packages can be manipulated in arbitrary ways.  An example of a useful
transformation is @dfn{input rewriting}, whereby the dependency tree of a
package is rewritten by replacing specific inputs by others:

@deffn {Scheme Procedure} package-input-rewriting @var{replacements} @
           [@var{rewrite-name}] Return a procedure that, when passed a package,
replaces its direct and indirect dependencies (but not its implicit inputs)
according to @var{replacements}.  @var{replacements} is a list of package
pairs; the first element of each pair is the package to replace, and the
second one is the replacement.

Optionally, @var{rewrite-name} is a one-argument procedure that takes the
name of a package and returns its new name after rewrite.
@end deffn

@noindent
Consider this example:

@example
(define libressl-instead-of-openssl
  ;; This is a procedure to replace OPENSSL by LIBRESSL,
  ;; recursively.
  (package-input-rewriting `((,openssl . ,libressl))))

(define git-with-libressl
  (libressl-instead-of-openssl git))
@end example

@noindent
Here we first define a rewriting procedure that replaces @var{openssl} with
@var{libressl}.  Then we use it to define a @dfn{variant} of the @var{git}
package that uses @var{libressl} instead of @var{openssl}.  This is exactly
what the @option{--with-input} command-line option does (@pxref{Paketumwandlungsoptionen, @option{--with-input}}).

A more generic procedure to rewrite a package dependency graph is
@code{package-mapping}: it supports arbitrary changes to nodes in the graph.

@deffn {Scheme Procedure} package-mapping @var{proc} [@var{cut?}]
Return a procedure that, given a package, applies @var{proc} to all the
packages depended on and returns the resulting package.  The procedure stops
recursion when @var{cut?} returns true for a given package.
@end deffn

@menu
* „package“-Referenz::   Der Datentyp für Pakete.
* „origin“-Referenz::    Datentyp für Paketursprünge.
@end menu


@node „package“-Referenz
@subsection @code{package} Reference

This section summarizes all the options available in @code{package}
declarations (@pxref{Pakete definieren}).

@deftp {Data Type} package
This is the data type representing a package recipe.

@table @asis
@item @code{name}
The name of the package, as a string.

@item @code{version}
The version of the package, as a string.

@item @code{source}
An object telling how the source code for the package should be acquired.
Most of the time, this is an @code{origin} object, which denotes a file
fetched from the Internet (@pxref{„origin“-Referenz}).  It can also be any
other ``file-like'' object such as a @code{local-file}, which denotes a file
from the local file system (@pxref{G-Ausdrücke, @code{local-file}}).

@item @code{build-system}
The build system that should be used to build the package (@pxref{Erstellungssysteme}).

@item @code{arguments} (default: @code{'()})
The arguments that should be passed to the build system.  This is a list,
typically containing sequential keyword-value pairs.

@item @code{inputs} (default: @code{'()})
@itemx @code{native-inputs} (default: @code{'()})
@itemx @code{propagated-inputs} (default: @code{'()})
@cindex inputs, of packages
These fields list dependencies of the package.  Each one is a list of
tuples, where each tuple has a label for the input (a string) as its first
element, a package, origin, or derivation as its second element, and
optionally the name of the output thereof that should be used, which
defaults to @code{"out"} (@pxref{Pakete mit mehreren Ausgaben.}, for more
on package outputs).  For example, the list below specifies three inputs:

@example
`(("libffi" ,libffi)
  ("libunistring" ,libunistring)
  ("glib:bin" ,glib "bin"))  ;the "bin" output of Glib
@end example

@cindex cross compilation, package dependencies
The distinction between @code{native-inputs} and @code{inputs} is necessary
when considering cross-compilation.  When cross-compiling, dependencies
listed in @code{inputs} are built for the @emph{target} architecture;
conversely, dependencies listed in @code{native-inputs} are built for the
architecture of the @emph{build} machine.

@code{native-inputs} is typically used to list tools needed at build time,
but not at run time, such as Autoconf, Automake, pkg-config, Gettext, or
Bison.  @command{guix lint} can report likely mistakes in this area
(@pxref{Aufruf von guix lint}).

@anchor{package-propagated-inputs}
Lastly, @code{propagated-inputs} is similar to @code{inputs}, but the
specified packages will be automatically installed alongside the package
they belong to (@pxref{package-cmd-propagated-inputs, @command{guix
package}}, for information on how @command{guix package} deals with
propagated inputs.)

For example this is necessary when a C/C++ library needs headers of another
library to compile, or when a pkg-config file refers to another one @i{via}
its @code{Requires} field.

Another example where @code{propagated-inputs} is useful is for languages
that lack a facility to record the run-time search path akin to the
@code{RUNPATH} of ELF files; this includes Guile, Python, Perl, and more.
To ensure that libraries written in those languages can find library code
they depend on at run time, run-time dependencies must be listed in
@code{propagated-inputs} rather than @code{inputs}.

@item @code{self-native-input?} (default: @code{#f})
This is a Boolean field telling whether the package should use itself as a
native input when cross-compiling.

@item @code{outputs} (default: @code{'("out")})
The list of output names of the package.  @xref{Pakete mit mehreren Ausgaben.}, for typical uses of additional outputs.

@item @code{native-search-paths} (default: @code{'()})
@itemx @code{search-paths} (default: @code{'()})
A list of @code{search-path-specification} objects describing search-path
environment variables honored by the package.

@item @code{replacement} (default: @code{#f})
This must be either @code{#f} or a package object that will be used as a
@dfn{replacement} for this package.  @xref{Sicherheitsaktualisierungen, grafts}, for
details.

@item @code{synopsis}
Eine einzeilige Beschreibung des Pakets.

@item @code{description}
Eine ausführlichere Beschreibung des Pakets.

@item @code{license}
@cindex license, of packages
The license of the package; a value from @code{(guix licenses)}, or a list
of such values.

@item @code{home-page}
The URL to the home-page of the package, as a string.

@item @code{supported-systems} (default: @var{%supported-systems})
The list of systems supported by the package, as strings of the form
@code{architecture-kernel}, for example @code{"x86_64-linux"}.

@item @code{maintainers} (default: @code{'()})
The list of maintainers of the package, as @code{maintainer} objects.

@item @code{location} (default: source location of the @code{package} form)
The source location of the package.  It is useful to override this when
inheriting from another package, in which case this field is not
automatically corrected.
@end table
@end deftp


@node „origin“-Referenz
@subsection @code{origin} Reference

This section summarizes all the options available in @code{origin}
declarations (@pxref{Pakete definieren}).

@deftp {Data Type} origin
This is the data type representing a source code origin.

@table @asis
@item @code{uri}
An object containing the URI of the source.  The object type depends on the
@code{method} (see below).  For example, when using the @var{url-fetch}
method of @code{(guix download)}, the valid @code{uri} values are: a URL
represented as a string, or a list thereof.

@item @code{method}
A procedure that handles the URI.

Examples include:

@table @asis
@item @var{url-fetch} from @code{(guix download)}
download a file from the HTTP, HTTPS, or FTP URL specified in the @code{uri}
field;

@vindex git-fetch
@item @var{git-fetch} from @code{(guix git-download)}
clone the Git version control repository, and check out the revision
specified in the @code{uri} field as a @code{git-reference} object; a
@code{git-reference} looks like this:

@example
(git-reference
  (url "git://git.debian.org/git/pkg-shadow/shadow")
  (commit "v4.1.5.1"))
@end example
@end table

@item @code{sha256}
A bytevector containing the SHA-256 hash of the source.  Typically the
@code{base32} form is used here to generate the bytevector from a base-32
string.

You can obtain this information using @code{guix download} (@pxref{Aufruf von guix download}) or @code{guix hash} (@pxref{Aufruf von guix hash}).

@item @code{file-name} (default: @code{#f})
The file name under which the source code should be saved.  When this is
@code{#f}, a sensible default value will be used in most cases.  In case the
source is fetched from a URL, the file name from the URL will be used.  For
version control checkouts, it is recommended to provide the file name
explicitly because the default is not very descriptive.

@item @code{patches} (default: @code{'()})
A list of file names, origins, or file-like objects (@pxref{G-Ausdrücke,
file-like objects}) pointing to patches to be applied to the source.

This list of patches must be unconditional.  In particular, it cannot depend
on the value of @code{%current-system} or @code{%current-target-system}.

@item @code{snippet} (default: @code{#f})
A G-expression (@pxref{G-Ausdrücke}) or S-expression that will be run in
the source directory.  This is a convenient way to modify the source,
sometimes more convenient than a patch.

@item @code{patch-flags} (default: @code{'("-p1")})
A list of command-line flags that should be passed to the @code{patch}
command.

@item @code{patch-inputs} (default: @code{#f})
Input packages or derivations to the patching process.  When this is
@code{#f}, the usual set of inputs necessary for patching are provided, such
as GNU@tie{}Patch.

@item @code{modules} (default: @code{'()})
A list of Guile modules that should be loaded during the patching process
and while running the code in the @code{snippet} field.

@item @code{patch-guile} (default: @code{#f})
The Guile package that should be used in the patching process.  When this is
@code{#f}, a sensible default is used.
@end table
@end deftp


@node Erstellungssysteme
@section Erstellungssysteme

@cindex build system
Each package definition specifies a @dfn{build system} and arguments for
that build system (@pxref{Pakete definieren}).  This @code{build-system}
field represents the build procedure of the package, as well as implicit
dependencies of that build procedure.

Build systems are @code{<build-system>} objects.  The interface to create
and manipulate them is provided by the @code{(guix build-system)} module,
and actual build systems are exported by specific modules.

@cindex bag (low-level package representation)
Under the hood, build systems first compile package objects to @dfn{bags}.
A @dfn{bag} is like a package, but with less ornamentation---in other words,
a bag is a lower-level representation of a package, which includes all the
inputs of that package, including some that were implicitly added by the
build system.  This intermediate representation is then compiled to a
derivation (@pxref{Ableitungen}).

Build systems accept an optional list of @dfn{arguments}.  In package
definitions, these are passed @i{via} the @code{arguments} field
(@pxref{Pakete definieren}).  They are typically keyword arguments
(@pxref{Optional Arguments, keyword arguments in Guile,, guile, GNU Guile
Reference Manual}).  The value of these arguments is usually evaluated in
the @dfn{build stratum}---i.e., by a Guile process launched by the daemon
(@pxref{Ableitungen}).

The main build system is @var{gnu-build-system}, which implements the
standard build procedure for GNU and many other packages.  It is provided by
the @code{(guix build-system gnu)} module.

@defvr {Scheme Variable} gnu-build-system
@var{gnu-build-system} represents the GNU Build System, and variants thereof
(@pxref{Configuration, configuration and makefile conventions,, standards,
GNU Coding Standards}).

@cindex build phases
In a nutshell, packages using it are configured, built, and installed with
the usual @code{./configure && make && make check && make install} command
sequence.  In practice, a few additional steps are often needed.  All these
steps are split up in separate @dfn{phases}, notably@footnote{Please see the
@code{(guix build gnu-build-system)} modules for more details about the
build phases.}:

@table @code
@item unpack
Unpack the source tarball, and change the current directory to the extracted
source tree.  If the source is actually a directory, copy it to the build
tree, and enter that directory.

@item patch-source-shebangs
Patch shebangs encountered in source files so they refer to the right store
file names.  For instance, this changes @code{#!/bin/sh} to
@code{#!/gnu/store/@dots{}-bash-4.3/bin/sh}.

@item configure
Run the @file{configure} script with a number of default options, such as
@code{--prefix=/gnu/store/@dots{}}, as well as the options specified by the
@code{#:configure-flags} argument.

@item build
Run @code{make} with the list of flags specified with @code{#:make-flags}.
If the @code{#:parallel-build?} argument is true (the default), build with
@code{make -j}.

@item check
Run @code{make check}, or some other target specified with
@code{#:test-target}, unless @code{#:tests? #f} is passed.  If the
@code{#:parallel-tests?} argument is true (the default), run @code{make
check -j}.

@item install
Run @code{make install} with the flags listed in @code{#:make-flags}.

@item patch-shebangs
Patch shebangs on the installed executable files.

@item strip
Strip debugging symbols from ELF files (unless @code{#:strip-binaries?} is
false), copying them to the @code{debug} output when available
(@pxref{Dateien zur Fehlersuche installieren}).
@end table

@vindex %standard-phases
The build-side module @code{(guix build gnu-build-system)} defines
@var{%standard-phases} as the default list of build phases.
@var{%standard-phases} is a list of symbol/procedure pairs, where the
procedure implements the actual phase.

The list of phases used for a particular package can be changed with the
@code{#:phases} parameter.  For instance, passing:

@example
#:phases (modify-phases %standard-phases (delete 'configure))
@end example

means that all the phases described above will be used, except the
@code{configure} phase.

In addition, this build system ensures that the ``standard'' environment for
GNU packages is available.  This includes tools such as GCC, libc,
Coreutils, Bash, Make, Diffutils, grep, and sed (see the @code{(guix
build-system gnu)} module for a complete list).  We call these the
@dfn{implicit inputs} of a package, because package definitions do not have
to mention them.
@end defvr

Other @code{<build-system>} objects are defined to support other conventions
and tools used by free software packages.  They inherit most of
@var{gnu-build-system}, and differ mainly in the set of inputs implicitly
added to the build process, and in the list of phases executed.  Some of
these build systems are listed below.

@defvr {Scheme Variable} ant-build-system
This variable is exported by @code{(guix build-system ant)}.  It implements
the build procedure for Java packages that can be built with
@url{http://ant.apache.org/, Ant build tool}.

It adds both @code{ant} and the @dfn{Java Development Kit} (JDK) as provided
by the @code{icedtea} package to the set of inputs.  Different packages can
be specified with the @code{#:ant} and @code{#:jdk} parameters,
respectively.

When the original package does not provide a suitable Ant build file, the
parameter @code{#:jar-name} can be used to generate a minimal Ant build file
@file{build.xml} with tasks to build the specified jar archive.  In this
case the parameter @code{#:source-dir} can be used to specify the source
sub-directory, defaulting to ``src''.

The @code{#:main-class} parameter can be used with the minimal ant buildfile
to specify the main class of the resulting jar.  This makes the jar file
executable.  The @code{#:test-include} parameter can be used to specify the
list of junit tests to run. It defaults to @code{(list "**/*Test.java")}.
The @code{#:test-exclude} can be used to disable some tests. It defaults to
@code{(list "**/Abstract*.java")}, because abstract classes cannot be run as
tests.

The parameter @code{#:build-target} can be used to specify the Ant task that
should be run during the @code{build} phase.  By default the ``jar'' task
will be run.

@end defvr

@defvr {Scheme Variable} android-ndk-build-system
@cindex Android distribution
@cindex Android NDK build system
This variable is exported by @code{(guix build-system android-ndk)}.  It
implements a build procedure for Android NDK (native development kit)
packages using a Guix-specific build process.

The build system assumes that packages install their public interface
(header) files to the subdirectory "include" of the "out" output and their
libraries to the subdirectory "lib" of the "out" output.

It's also assumed that the union of all the dependencies of a package has no
conflicting files.

For the time being, cross-compilation is not supported - so right now the
libraries and header files are assumed to be host tools.

@end defvr

@defvr {Scheme Variable} asdf-build-system/source
@defvrx {Scheme Variable} asdf-build-system/sbcl
@defvrx {Scheme Variable} asdf-build-system/ecl

These variables, exported by @code{(guix build-system asdf)}, implement
build procedures for Common Lisp packages using
@url{https://common-lisp.net/project/asdf/, ``ASDF''}. ASDF is a system
definition facility for Common Lisp programs and libraries.

The @code{asdf-build-system/source} system installs the packages in source
form, and can be loaded using any common lisp implementation, via ASDF.  The
others, such as @code{asdf-build-system/sbcl}, install binary systems in the
format which a particular implementation understands.  These build systems
can also be used to produce executable programs, or lisp images which
contain a set of packages pre-loaded.

The build system uses naming conventions.  For binary packages, the package
name should be prefixed with the lisp implementation, such as @code{sbcl-}
for @code{asdf-build-system/sbcl}.

Additionally, the corresponding source package should be labeled using the
same convention as python packages (see @ref{Python-Module}), using the
@code{cl-} prefix.

For binary packages, each system should be defined as a Guix package.  If
one package @code{origin} contains several systems, package variants can be
created in order to build all the systems.  Source packages, which use
@code{asdf-build-system/source}, may contain several systems.

In order to create executable programs and images, the build-side procedures
@code{build-program} and @code{build-image} can be used.  They should be
called in a build phase after the @code{create-symlinks} phase, so that the
system which was just built can be used within the resulting image.
@code{build-program} requires a list of Common Lisp expressions to be passed
as the @code{#:entry-program} argument.

If the system is not defined within its own @code{.asd} file of the same
name, then the @code{#:asd-file} parameter should be used to specify which
file the system is defined in.  Furthermore, if the package defines a system
for its tests in a separate file, it will be loaded before the tests are run
if it is specified by the @code{#:test-asd-file} parameter.  If it is not
set, the files @code{<system>-tests.asd}, @code{<system>-test.asd},
@code{tests.asd}, and @code{test.asd} will be tried if they exist.

If for some reason the package must be named in a different way than the
naming conventions suggest, the @code{#:asd-system-name} parameter can be
used to specify the name of the system.

@end defvr

@defvr {Scheme Variable} cargo-build-system
@cindex Rust programming language
@cindex Cargo (Rust build system)
This variable is exported by @code{(guix build-system cargo)}.  It supports
builds of packages using Cargo, the build tool of the
@uref{https://www.rust-lang.org, Rust programming language}.

In its @code{configure} phase, this build system replaces dependencies
specified in the @file{Carto.toml} file with inputs to the Guix package.
The @code{install} phase installs the binaries, and it also installs the
source code and @file{Cargo.toml} file.
@end defvr

@defvr {Scheme Variable} cmake-build-system
This variable is exported by @code{(guix build-system cmake)}.  It
implements the build procedure for packages using the
@url{http://www.cmake.org, CMake build tool}.

It automatically adds the @code{cmake} package to the set of inputs.  Which
package is used can be specified with the @code{#:cmake} parameter.

The @code{#:configure-flags} parameter is taken as a list of flags passed to
the @command{cmake} command.  The @code{#:build-type} parameter specifies in
abstract terms the flags passed to the compiler; it defaults to
@code{"RelWithDebInfo"} (short for ``release mode with debugging
information''), which roughly means that code is compiled with @code{-O2
-g}, as is the case for Autoconf-based packages by default.
@end defvr

@defvr {Scheme Variable} go-build-system
This variable is exported by @code{(guix build-system go)}.  It implements a
build procedure for Go packages using the standard
@url{https://golang.org/cmd/go/#hdr-Compile_packages_and_dependencies, Go
build mechanisms}.

The user is expected to provide a value for the key @code{#:import-path}
and, in some cases, @code{#:unpack-path}.  The
@url{https://golang.org/doc/code.html#ImportPaths, import path} corresponds
to the file system path expected by the package's build scripts and any
referring packages, and provides a unique way to refer to a Go package.  It
is typically based on a combination of the package source code's remote URI
and file system hierarchy structure.  In some cases, you will need to unpack
the package's source code to a different directory structure than the one
indicated by the import path, and @code{#:unpack-path} should be used in
such cases.

Packages that provide Go libraries should be installed along with their
source code.  The key @code{#:install-source?}, which defaults to @code{#t},
controls whether or not the source code is installed.  It can be set to
@code{#f} for packages that only provide executable files.
@end defvr

@defvr {Scheme Variable} glib-or-gtk-build-system
This variable is exported by @code{(guix build-system glib-or-gtk)}.  It is
intended for use with packages making use of GLib or GTK+.

This build system adds the following two phases to the ones defined by
@var{gnu-build-system}:

@table @code
@item glib-or-gtk-wrap
The phase @code{glib-or-gtk-wrap} ensures that programs in @file{bin/} are
able to find GLib ``schemas'' and
@uref{https://developer.gnome.org/gtk3/stable/gtk-running.html, GTK+
modules}.  This is achieved by wrapping the programs in launch scripts that
appropriately set the @code{XDG_DATA_DIRS} and @code{GTK_PATH} environment
variables.

It is possible to exclude specific package outputs from that wrapping
process by listing their names in the
@code{#:glib-or-gtk-wrap-excluded-outputs} parameter.  This is useful when
an output is known not to contain any GLib or GTK+ binaries, and where
wrapping would gratuitously add a dependency of that output on GLib and
GTK+.

@item glib-or-gtk-compile-schemas
The phase @code{glib-or-gtk-compile-schemas} makes sure that all
@uref{https://developer.gnome.org/gio/stable/glib-compile-schemas.html,
GSettings schemas} of GLib are compiled.  Compilation is performed by the
@command{glib-compile-schemas} program.  It is provided by the package
@code{glib:bin} which is automatically imported by the build system.  The
@code{glib} package providing @command{glib-compile-schemas} can be
specified with the @code{#:glib} parameter.
@end table

Both phases are executed after the @code{install} phase.
@end defvr

@defvr {Scheme Variable} guile-build-system
This build system is for Guile packages that consist exclusively of Scheme
code and that are so lean that they don't even have a makefile, let alone a
@file{configure} script.  It compiles Scheme code using @command{guild
compile} (@pxref{Compilation,,, guile, GNU Guile Reference Manual}) and
installs the @file{.scm} and @file{.go} files in the right place.  It also
installs documentation.

This build system supports cross-compilation by using the @code{--target}
option of @command{guild compile}.

Packages built with @code{guile-build-system} must provide a Guile package
in their @code{native-inputs} field.
@end defvr

@defvr {Scheme Variable} minify-build-system
This variable is exported by @code{(guix build-system minify)}.  It
implements a minification procedure for simple JavaScript packages.

It adds @code{uglify-js} to the set of inputs and uses it to compress all
JavaScript files in the @file{src} directory.  A different minifier package
can be specified with the @code{#:uglify-js} parameter, but it is expected
that the package writes the minified code to the standard output.

When the input JavaScript files are not all located in the @file{src}
directory, the parameter @code{#:javascript-files} can be used to specify a
list of file names to feed to the minifier.
@end defvr

@defvr {Scheme Variable} ocaml-build-system
This variable is exported by @code{(guix build-system ocaml)}.  It
implements a build procedure for @uref{https://ocaml.org, OCaml} packages,
which consists of choosing the correct set of commands to run for each
package.  OCaml packages can expect many different commands to be run.  This
build system will try some of them.

When the package has a @file{setup.ml} file present at the top-level, it
will run @code{ocaml setup.ml -configure}, @code{ocaml setup.ml -build} and
@code{ocaml setup.ml -install}.  The build system will assume that this file
was generated by @uref{http://oasis.forge.ocamlcore.org/, OASIS} and will
take care of setting the prefix and enabling tests if they are not
disabled.  You can pass configure and build flags with the
@code{#:configure-flags} and @code{#:build-flags}.  The @code{#:test-flags}
key can be passed to change the set of flags used to enable tests.  The
@code{#:use-make?} key can be used to bypass this system in the build and
install phases.

When the package has a @file{configure} file, it is assumed that it is a
hand-made configure script that requires a different argument format than in
the @code{gnu-build-system}.  You can add more flags with the
@code{#:configure-flags} key.

When the package has a @file{Makefile} file (or @code{#:use-make?} is
@code{#t}), it will be used and more flags can be passed to the build and
install phases with the @code{#:make-flags} key.

Finally, some packages do not have these files and use a somewhat standard
location for its build system.  In that case, the build system will run
@code{ocaml pkg/pkg.ml} or @code{ocaml pkg/build.ml} and take care of
providing the path to the required findlib module.  Additional flags can be
passed via the @code{#:build-flags} key.  Install is taken care of by
@command{opam-installer}.  In this case, the @code{opam} package must be
added to the @code{native-inputs} field of the package definition.

Note that most OCaml packages assume they will be installed in the same
directory as OCaml, which is not what we want in guix.  In particular, they
will install @file{.so} files in their module's directory, which is usually
fine because it is in the OCaml compiler directory.  In guix though, these
libraries cannot be found and we use @code{CAML_LD_LIBRARY_PATH}.  This
variable points to @file{lib/ocaml/site-lib/stubslibs} and this is where
@file{.so} libraries should be installed.
@end defvr

@defvr {Scheme Variable} python-build-system
This variable is exported by @code{(guix build-system python)}.  It
implements the more or less standard build procedure used by Python
packages, which consists in running @code{python setup.py build} and then
@code{python setup.py install --prefix=/gnu/store/@dots{}}.

For packages that install stand-alone Python programs under @code{bin/}, it
takes care of wrapping these programs so that their @code{PYTHONPATH}
environment variable points to all the Python libraries they depend on.

Which Python package is used to perform the build can be specified with the
@code{#:python} parameter.  This is a useful way to force a package to be
built for a specific version of the Python interpreter, which might be
necessary if the package is only compatible with a single interpreter
version.

By default guix calls @code{setup.py} under control of @code{setuptools},
much like @command{pip} does.  Some packages are not compatible with
setuptools (and pip), thus you can disable this by setting the
@code{#:use-setuptools} parameter to @code{#f}.
@end defvr

@defvr {Scheme Variable} perl-build-system
This variable is exported by @code{(guix build-system perl)}.  It implements
the standard build procedure for Perl packages, which either consists in
running @code{perl Build.PL --prefix=/gnu/store/@dots{}}, followed by
@code{Build} and @code{Build install}; or in running @code{perl Makefile.PL
PREFIX=/gnu/store/@dots{}}, followed by @code{make} and @code{make install},
depending on which of @code{Build.PL} or @code{Makefile.PL} is present in
the package distribution.  Preference is given to the former if both
@code{Build.PL} and @code{Makefile.PL} exist in the package distribution.
This preference can be reversed by specifying @code{#t} for the
@code{#:make-maker?} parameter.

The initial @code{perl Makefile.PL} or @code{perl Build.PL} invocation
passes flags specified by the @code{#:make-maker-flags} or
@code{#:module-build-flags} parameter, respectively.

Which Perl package is used can be specified with @code{#:perl}.
@end defvr

@defvr {Scheme Variable} r-build-system
This variable is exported by @code{(guix build-system r)}.  It implements
the build procedure used by @uref{http://r-project.org, R} packages, which
essentially is little more than running @code{R CMD INSTALL
--library=/gnu/store/@dots{}} in an environment where @code{R_LIBS_SITE}
contains the paths to all R package inputs.  Tests are run after
installation using the R function @code{tools::testInstalledPackage}.
@end defvr

@defvr {Scheme Variable} texlive-build-system
This variable is exported by @code{(guix build-system texlive)}.  It is used
to build TeX packages in batch mode with a specified engine.  The build
system sets the @code{TEXINPUTS} variable to find all TeX source files in
the inputs.

By default it runs @code{luatex} on all files ending on @code{ins}.  A
different engine and format can be specified with the @code{#:tex-format}
argument.  Different build targets can be specified with the
@code{#:build-targets} argument, which expects a list of file names.  The
build system adds only @code{texlive-bin} and @code{texlive-latex-base}
(both from @code{(gnu packages tex}) to the inputs.  Both can be overridden
with the arguments @code{#:texlive-bin} and @code{#:texlive-latex-base},
respectively.

The @code{#:tex-directory} parameter tells the build system where to install
the built files under the texmf tree.
@end defvr

@defvr {Scheme Variable} ruby-build-system
This variable is exported by @code{(guix build-system ruby)}.  It implements
the RubyGems build procedure used by Ruby packages, which involves running
@code{gem build} followed by @code{gem install}.

The @code{source} field of a package that uses this build system typically
references a gem archive, since this is the format that Ruby developers use
when releasing their software.  The build system unpacks the gem archive,
potentially patches the source, runs the test suite, repackages the gem, and
installs it.  Additionally, directories and tarballs may be referenced to
allow building unreleased gems from Git or a traditional source release
tarball.

Which Ruby package is used can be specified with the @code{#:ruby}
parameter.  A list of additional flags to be passed to the @command{gem}
command can be specified with the @code{#:gem-flags} parameter.
@end defvr

@defvr {Scheme Variable} waf-build-system
This variable is exported by @code{(guix build-system waf)}.  It implements
a build procedure around the @code{waf} script.  The common
phases---@code{configure}, @code{build}, and @code{install}---are
implemented by passing their names as arguments to the @code{waf} script.

The @code{waf} script is executed by the Python interpreter.  Which Python
package is used to run the script can be specified with the @code{#:python}
parameter.
@end defvr

@defvr {Scheme Variable} scons-build-system
This variable is exported by @code{(guix build-system scons)}.  It
implements the build procedure used by the SCons software construction
tool.  This build system runs @code{scons} to build the package, @code{scons
test} to run tests, and then @code{scons install} to install the package.

Additional flags to be passed to @code{scons} can be specified with the
@code{#:scons-flags} parameter.  The version of Python used to run SCons can
be specified by selecting the appropriate SCons package with the
@code{#:scons} parameter.
@end defvr

@defvr {Scheme Variable} haskell-build-system
This variable is exported by @code{(guix build-system haskell)}.  It
implements the Cabal build procedure used by Haskell packages, which
involves running @code{runhaskell Setup.hs configure
--prefix=/gnu/store/@dots{}} and @code{runhaskell Setup.hs build}.  Instead
of installing the package by running @code{runhaskell Setup.hs install}, to
avoid trying to register libraries in the read-only compiler store
directory, the build system uses @code{runhaskell Setup.hs copy}, followed
by @code{runhaskell Setup.hs register}.  In addition, the build system
generates the package documentation by running @code{runhaskell Setup.hs
haddock}, unless @code{#:haddock? #f} is passed.  Optional Haddock
parameters can be passed with the help of the @code{#:haddock-flags}
parameter.  If the file @code{Setup.hs} is not found, the build system looks
for @code{Setup.lhs} instead.

Which Haskell compiler is used can be specified with the @code{#:haskell}
parameter which defaults to @code{ghc}.
@end defvr

@defvr {Scheme Variable} dub-build-system
This variable is exported by @code{(guix build-system dub)}.  It implements
the Dub build procedure used by D packages, which involves running @code{dub
build} and @code{dub run}.  Installation is done by copying the files
manually.

Which D compiler is used can be specified with the @code{#:ldc} parameter
which defaults to @code{ldc}.
@end defvr

@defvr {Scheme Variable} emacs-build-system
This variable is exported by @code{(guix build-system emacs)}.  It
implements an installation procedure similar to the packaging system of
Emacs itself (@pxref{Packages,,, emacs, The GNU Emacs Manual}).

It first creates the @code{@var{package}-autoloads.el} file, then it byte
compiles all Emacs Lisp files.  Differently from the Emacs packaging system,
the Info documentation files are moved to the standard documentation
directory and the @file{dir} file is deleted.  Each package is installed in
its own directory under @file{share/emacs/site-lisp/guix.d}.
@end defvr

@defvr {Scheme Variable} font-build-system
This variable is exported by @code{(guix build-system font)}.  It implements
an installation procedure for font packages where upstream provides
pre-compiled TrueType, OpenType, etc. font files that merely need to be
copied into place.  It copies font files to standard locations in the output
directory.
@end defvr

@defvr {Scheme Variable} meson-build-system
This variable is exported by @code{(guix build-system meson)}.  It
implements the build procedure for packages that use
@url{http://mesonbuild.com, Meson} as their build system.

It adds both Meson and @uref{https://ninja-build.org/, Ninja} to the set of
inputs, and they can be changed with the parameters @code{#:meson} and
@code{#:ninja} if needed.  The default Meson is @code{meson-for-build},
which is special because it doesn't clear the @code{RUNPATH} of binaries and
libraries when they are installed.

This build system is an extension of @var{gnu-build-system}, but with the
following phases changed to some specific for Meson:

@table @code

@item configure
The phase runs @code{meson} with the flags specified in
@code{#:configure-flags}.  The flag @code{--build-type} is always set to
@code{plain} unless something else is specified in @code{#:build-type}.

@item build
The phase runs @code{ninja} to build the package in parallel by default, but
this can be changed with @code{#:parallel-build?}.

@item check
The phase runs @code{ninja} with the target specified in
@code{#:test-target}, which is @code{"test"} by default.

@item install
The phase runs @code{ninja install} and can not be changed.
@end table

Apart from that, the build system also adds the following phases:

@table @code

@item fix-runpath
This phase ensures that all binaries can find the libraries they need.  It
searches for required libraries in subdirectories of the package being
built, and adds those to @code{RUNPATH} where needed.  It also removes
references to libraries left over from the build phase by
@code{meson-for-build}, such as test dependencies, that aren't actually
required for the program to run.

@item glib-or-gtk-wrap
This phase is the phase provided by @code{glib-or-gtk-build-system}, and it
is not enabled by default.  It can be enabled with @code{#:glib-or-gtk?}.

@item glib-or-gtk-compile-schemas
This phase is the phase provided by @code{glib-or-gtk-build-system}, and it
is not enabled by default.  It can be enabled with @code{#:glib-or-gtk?}.
@end table
@end defvr

Lastly, for packages that do not need anything as sophisticated, a
``trivial'' build system is provided.  It is trivial in the sense that it
provides basically no support: it does not pull any implicit inputs, and
does not have a notion of build phases.

@defvr {Scheme Variable} trivial-build-system
This variable is exported by @code{(guix build-system trivial)}.

This build system requires a @code{#:builder} argument.  This argument must
be a Scheme expression that builds the package output(s)---as with
@code{build-expression->derivation} (@pxref{Ableitungen,
@code{build-expression->derivation}}).
@end defvr

@node Der Store
@section Der Store

@cindex Store
@cindex store items
@cindex store paths

Conceptually, the @dfn{store} is the place where derivations that have been
built successfully are stored---by default, @file{/gnu/store}.
Sub-directories in the store are referred to as @dfn{store items} or
sometimes @dfn{store paths}.  The store has an associated database that
contains information such as the store paths referred to by each store path,
and the list of @emph{valid} store items---results of successful builds.
This database resides in @file{@var{localstatedir}/guix/db}, where
@var{localstatedir} is the state directory specified @i{via}
@option{--localstatedir} at configure time, usually @file{/var}.

The store is @emph{always} accessed by the daemon on behalf of its clients
(@pxref{Aufruf des guix-daemon}).  To manipulate the store, clients connect to
the daemon over a Unix-domain socket, send requests to it, and read the
result---these are remote procedure calls, or RPCs.

@quotation Anmerkung
Users must @emph{never} modify files under @file{/gnu/store} directly.  This
would lead to inconsistencies and break the immutability assumptions of
Guix's functional model (@pxref{Einführung}).

@xref{Aufruf von guix gc, @command{guix gc --verify}}, for information on how
to check the integrity of the store and attempt recovery from accidental
modifications.
@end quotation

The @code{(guix store)} module provides procedures to connect to the daemon,
and to perform RPCs.  These are described below.  By default,
@code{open-connection}, and thus all the @command{guix} commands, connect to
the local daemon or to the URI specified by the @code{GUIX_DAEMON_SOCKET}
environment variable.

@defvr {Environment Variable} GUIX_DAEMON_SOCKET
When set, the value of this variable should be a file name or a URI
designating the daemon endpoint.  When it is a file name, it denotes a
Unix-domain socket to connect to.  In addition to file names, the supported
URI schemes are:

@table @code
@item file
@itemx unix
These are for Unix-domain sockets.
@code{file:///var/guix/daemon-socket/socket} is equivalent to
@file{/var/guix/daemon-socket/socket}.

@item guix
@cindex Daemon, Fernzugriff
@cindex Fernzugriff auf den Daemon
@cindex Daemon, Einrichten auf Clustern
@cindex Cluster, Einrichtung des Daemons
These URIs denote connections over TCP/IP, without encryption nor
authentication of the remote host.  The URI must specify the host name and
optionally a port number (by default port 44146 is used):

@example
guix://master.guix.example.org:1234
@end example

This setup is suitable on local networks, such as clusters, where only
trusted nodes may connect to the build daemon at
@code{master.guix.example.org}.

The @code{--listen} option of @command{guix-daemon} can be used to instruct
it to listen for TCP connections (@pxref{Aufruf des guix-daemon,
@code{--listen}}).

@item ssh
@cindex SSH access to build daemons
These URIs allow you to connect to a remote daemon over SSH@footnote{This
feature requires Guile-SSH (@pxref{Voraussetzungen}).}.  A typical URL might
look like this:

@example
ssh://charlie@@guix.example.org:22
@end example

As for @command{guix copy}, the usual OpenSSH client configuration files are
honored (@pxref{Aufruf von guix copy}).
@end table

Additional URI schemes may be supported in the future.

@c XXX: Remove this note when the protocol incurs fewer round trips
@c and when (guix derivations) no longer relies on file system access.
@quotation Anmerkung
The ability to connect to remote build daemons is considered experimental as
of @value{VERSION}.  Please get in touch with us to share any problems or
suggestions you may have (@pxref{Mitwirken}).
@end quotation
@end defvr

@deffn {Scheme Procedure} open-connection [@var{uri}] [#:reserve-space? #t]
Connect to the daemon over the Unix-domain socket at @var{uri} (a string).
When @var{reserve-space?} is true, instruct it to reserve a little bit of
extra space on the file system so that the garbage collector can still
operate should the disk become full.  Return a server object.

@var{file} defaults to @var{%default-socket-path}, which is the normal
location given the options that were passed to @command{configure}.
@end deffn

@deffn {Scheme Procedure} close-connection @var{server}
Close the connection to @var{server}.
@end deffn

@defvr {Scheme Variable} current-build-output-port
This variable is bound to a SRFI-39 parameter, which refers to the port
where build and error logs sent by the daemon should be written.
@end defvr

Procedures that make RPCs all take a server object as their first argument.

@deffn {Scheme Procedure} valid-path? @var{server} @var{path}
@cindex invalid store items
Return @code{#t} when @var{path} designates a valid store item and @code{#f}
otherwise (an invalid item may exist on disk but still be invalid, for
instance because it is the result of an aborted or failed build.)

A @code{&nix-protocol-error} condition is raised if @var{path} is not
prefixed by the store directory (@file{/gnu/store}).
@end deffn

@deffn {Scheme Procedure} add-text-to-store @var{server} @var{name} @var{text} [@var{references}]
Add @var{text} under file @var{name} in the store, and return its store
path.  @var{references} is the list of store paths referred to by the
resulting store path.
@end deffn

@deffn {Scheme Procedure} build-derivations @var{server} @var{derivations}
Build @var{derivations} (a list of @code{<derivation>} objects or derivation
paths), and return when the worker is done building them.  Return @code{#t}
on success.
@end deffn

Note that the @code{(guix monads)} module provides a monad as well as
monadic versions of the above procedures, with the goal of making it more
convenient to work with code that accesses the store (@pxref{Die Store-Monade}).

@c FIXME
@i{This section is currently incomplete.}

@node Ableitungen
@section Ableitungen

@cindex derivations
Low-level build actions and the environment in which they are performed are
represented by @dfn{derivations}.  A derivation contains the following
pieces of information:

@itemize
@item
The outputs of the derivation---derivations produce at least one file or
directory in the store, but may produce more.

@item
The inputs of the derivations, which may be other derivations or plain files
in the store (patches, build scripts, etc.)

@item
The system type targeted by the derivation---e.g., @code{x86_64-linux}.

@item
The file name of a build script in the store, along with the arguments to be
passed.

@item
A list of environment variables to be defined.

@end itemize

@cindex derivation path
Derivations allow clients of the daemon to communicate build actions to the
store.  They exist in two forms: as an in-memory representation, both on the
client- and daemon-side, and as files in the store whose name end in
@code{.drv}---these files are referred to as @dfn{derivation paths}.
Derivations paths can be passed to the @code{build-derivations} procedure to
perform the build actions they prescribe (@pxref{Der Store}).

@cindex fixed-output derivations
Operations such as file downloads and version-control checkouts for which
the expected content hash is known in advance are modeled as
@dfn{fixed-output derivations}.  Unlike regular derivations, the outputs of
a fixed-output derivation are independent of its inputs---e.g., a source
code download produces the same result regardless of the download method and
tools being used.

The @code{(guix derivations)} module provides a representation of
derivations as Scheme objects, along with procedures to create and otherwise
manipulate derivations.  The lowest-level primitive to create a derivation
is the @code{derivation} procedure:

@deffn {Scheme Procedure} derivation @var{store} @var{name} @var{builder} @
  @var{args} [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] @ [#:recursive?
#f] [#:inputs '()] [#:env-vars '()] @ [#:system (%current-system)]
[#:references-graphs #f] @ [#:allowed-references #f]
[#:disallowed-references #f] @ [#:leaked-env-vars #f] [#:local-build? #f] @
[#:substitutable? #t] Build a derivation with the given arguments, and
return the resulting @code{<derivation>} object.

When @var{hash} and @var{hash-algo} are given, a @dfn{fixed-output
derivation} is created---i.e., one whose result is known in advance, such as
a file download.  If, in addition, @var{recursive?} is true, then that fixed
output may be an executable file or a directory and @var{hash} must be the
hash of an archive containing this output.

When @var{references-graphs} is true, it must be a list of file name/store
path pairs.  In that case, the reference graph of each store path is
exported in the build environment in the corresponding file, in a simple
text format.

When @var{allowed-references} is true, it must be a list of store items or
outputs that the derivation's output may refer to.  Likewise,
@var{disallowed-references}, if true, must be a list of things the outputs
may @emph{not} refer to.

When @var{leaked-env-vars} is true, it must be a list of strings denoting
environment variables that are allowed to ``leak'' from the daemon's
environment to the build environment.  This is only applicable to
fixed-output derivations---i.e., when @var{hash} is true.  The main use is
to allow variables such as @code{http_proxy} to be passed to derivations
that download files.

When @var{local-build?} is true, declare that the derivation is not a good
candidate for offloading and should rather be built locally (@pxref{Auslagern des Daemons einrichten}).  This is the case for small derivations where the costs of
data transfers would outweigh the benefits.

When @var{substitutable?} is false, declare that substitutes of the
derivation's output should not be used (@pxref{Substitute}).  This is
useful, for instance, when building packages that capture details of the
host CPU instruction set.
@end deffn

@noindent
Here's an example with a shell script as its builder, assuming @var{store}
is an open connection to the daemon, and @var{bash} points to a Bash
executable in the store:

@lisp
(use-modules (guix utils)
             (guix store)
             (guix derivations))

(let ((builder   ; add the Bash script to the store
        (add-text-to-store store "my-builder.sh"
                           "echo hello world > $out\n" '())))
  (derivation store "foo"
              bash `("-e" ,builder)
              #:inputs `((,bash) (,builder))
              #:env-vars '(("HOME" . "/homeless"))))
@result{} #<derivation /gnu/store/@dots{}-foo.drv => /gnu/store/@dots{}-foo>
@end lisp

As can be guessed, this primitive is cumbersome to use directly.  A better
approach is to write build scripts in Scheme, of course! The best course of
action for that is to write the build code as a ``G-expression'', and to
pass it to @code{gexp->derivation}.  For more information,
@pxref{G-Ausdrücke}.

Once upon a time, @code{gexp->derivation} did not exist and constructing
derivations with build code written in Scheme was achieved with
@code{build-expression->derivation}, documented below.  This procedure is
now deprecated in favor of the much nicer @code{gexp->derivation}.

@deffn {Scheme Procedure} build-expression->derivation @var{store} @
       @var{name} @var{exp} @ [#:system (%current-system)] [#:inputs '()] @
[#:outputs '("out")] [#:hash #f] [#:hash-algo #f] @ [#:recursive? #f]
[#:env-vars '()] [#:modules '()] @ [#:references-graphs #f]
[#:allowed-references #f] @ [#:disallowed-references #f] @ [#:local-build?
#f] [#:substitutable? #t] [#:guile-for-build #f] Return a derivation that
executes Scheme expression @var{exp} as a builder for derivation
@var{name}.  @var{inputs} must be a list of @code{(name drv-path sub-drv)}
tuples; when @var{sub-drv} is omitted, @code{"out"} is assumed.
@var{modules} is a list of names of Guile modules from the current search
path to be copied in the store, compiled, and made available in the load
path during the execution of @var{exp}---e.g., @code{((guix build utils)
(guix build gnu-build-system))}.

@var{exp} is evaluated in an environment where @code{%outputs} is bound to a
list of output/path pairs, and where @code{%build-inputs} is bound to a list
of string/output-path pairs made from @var{inputs}.  Optionally,
@var{env-vars} is a list of string pairs specifying the name and value of
environment variables visible to the builder.  The builder terminates by
passing the result of @var{exp} to @code{exit}; thus, when @var{exp} returns
@code{#f}, the build is considered to have failed.

@var{exp} is built using @var{guile-for-build} (a derivation).  When
@var{guile-for-build} is omitted or is @code{#f}, the value of the
@code{%guile-for-build} fluid is used instead.

See the @code{derivation} procedure for the meaning of
@var{references-graphs}, @var{allowed-references},
@var{disallowed-references}, @var{local-build?}, and @var{substitutable?}.
@end deffn

@noindent
Here's an example of a single-output derivation that creates a directory
containing one file:

@lisp
(let ((builder '(let ((out (assoc-ref %outputs "out")))
                  (mkdir out)    ; create /gnu/store/@dots{}-goo
                  (call-with-output-file (string-append out "/test")
                    (lambda (p)
                      (display '(hello guix) p))))))
  (build-expression->derivation store "goo" builder))

@result{} #<derivation /gnu/store/@dots{}-goo.drv => @dots{}>
@end lisp


@node Die Store-Monade
@section Die Store-Monade

@cindex monad

The procedures that operate on the store described in the previous sections
all take an open connection to the build daemon as their first argument.
Although the underlying model is functional, they either have side effects
or depend on the current state of the store.

The former is inconvenient: the connection to the build daemon has to be
carried around in all those functions, making it impossible to compose
functions that do not take that parameter with functions that do.  The
latter can be problematic: since store operations have side effects and/or
depend on external state, they have to be properly sequenced.

@cindex monadic values
@cindex monadic functions
This is where the @code{(guix monads)} module comes in.  This module
provides a framework for working with @dfn{monads}, and a particularly
useful monad for our uses, the @dfn{store monad}.  Monads are a construct
that allows two things: associating ``context'' with values (in our case,
the context is the store), and building sequences of computations (here
computations include accesses to the store).  Values in a monad---values
that carry this additional context---are called @dfn{monadic values};
procedures that return such values are called @dfn{monadic procedures}.

Consider this ``normal'' procedure:

@example
(define (sh-symlink store)
  ;; Return a derivation that symlinks the 'bash' executable.
  (let* ((drv (package-derivation store bash))
         (out (derivation->output-path drv))
         (sh  (string-append out "/bin/bash")))
    (build-expression->derivation store "sh"
                                  `(symlink ,sh %output))))
@end example

Using @code{(guix monads)} and @code{(guix gexp)}, it may be rewritten as a
monadic function:

@example
(define (sh-symlink)
  ;; Same, but return a monadic value.
  (mlet %store-monad ((drv (package->derivation bash)))
    (gexp->derivation "sh"
                      #~(symlink (string-append #$drv "/bin/bash")
                                 #$output))))
@end example

There are several things to note in the second version: the @code{store}
parameter is now implicit and is ``threaded'' in the calls to the
@code{package->derivation} and @code{gexp->derivation} monadic procedures,
and the monadic value returned by @code{package->derivation} is @dfn{bound}
using @code{mlet} instead of plain @code{let}.

As it turns out, the call to @code{package->derivation} can even be omitted
since it will take place implicitly, as we will see later
(@pxref{G-Ausdrücke}):

@example
(define (sh-symlink)
  (gexp->derivation "sh"
                    #~(symlink (string-append #$bash "/bin/bash")
                               #$output)))
@end example

@c See
@c <https://syntaxexclamation.wordpress.com/2014/06/26/escaping-continuations/>
@c for the funny quote.
Calling the monadic @code{sh-symlink} has no effect.  As someone once said,
``you exit a monad like you exit a building on fire: by running''.  So, to
exit the monad and get the desired effect, one must use
@code{run-with-store}:

@example
(run-with-store (open-connection) (sh-symlink))
@result{} /gnu/store/...-sh-symlink
@end example

Note that the @code{(guix monad-repl)} module extends the Guile REPL with
new ``meta-commands'' to make it easier to deal with monadic procedures:
@code{run-in-store}, and @code{enter-store-monad}.  The former is used to
``run'' a single monadic value through the store:

@example
scheme@@(guile-user)> ,run-in-store (package->derivation hello)
$1 = #<derivation /gnu/store/@dots{}-hello-2.9.drv => @dots{}>
@end example

The latter enters a recursive REPL, where all the return values are
automatically run through the store:

@example
scheme@@(guile-user)> ,enter-store-monad
store-monad@@(guile-user) [1]> (package->derivation hello)
$2 = #<derivation /gnu/store/@dots{}-hello-2.9.drv => @dots{}>
store-monad@@(guile-user) [1]> (text-file "foo" "Hello!")
$3 = "/gnu/store/@dots{}-foo"
store-monad@@(guile-user) [1]> ,q
scheme@@(guile-user)>
@end example

@noindent
Note that non-monadic values cannot be returned in the @code{store-monad}
REPL.

The main syntactic forms to deal with monads in general are provided by the
@code{(guix monads)} module and are described below.

@deffn {Scheme Syntax} with-monad @var{monad} @var{body} ...
Evaluate any @code{>>=} or @code{return} forms in @var{body} as being in
@var{monad}.
@end deffn

@deffn {Scheme Syntax} return @var{val}
Return a monadic value that encapsulates @var{val}.
@end deffn

@deffn {Scheme Syntax} >>= @var{mval} @var{mproc} ...
@dfn{Bind} monadic value @var{mval}, passing its ``contents'' to monadic
procedures @var{mproc}@dots{}@footnote{This operation is commonly referred
to as ``bind'', but that name denotes an unrelated procedure in Guile.  Thus
we use this somewhat cryptic symbol inherited from the Haskell language.}.
There can be one @var{mproc} or several of them, as in this example:

@example
(run-with-state
    (with-monad %state-monad
      (>>= (return 1)
           (lambda (x) (return (+ 1 x)))
           (lambda (x) (return (* 2 x)))))
  'some-state)

@result{} 4
@result{} some-state
@end example
@end deffn

@deffn {Scheme Syntax} mlet @var{monad} ((@var{var} @var{mval}) ...) @
       @var{body} ...
@deffnx {Scheme Syntax} mlet* @var{monad} ((@var{var} @var{mval}) ...) @
       @var{body} ...  Bind the variables @var{var} to the monadic values
@var{mval} in @var{body}, which is a sequence of expressions.  As with the
bind operator, this can be thought of as ``unpacking'' the raw, non-monadic
value ``contained'' in @var{mval} and making @var{var} refer to that raw,
non-monadic value within the scope of the @var{body}.  The form (@var{var}
-> @var{val}) binds @var{var} to the ``normal'' value @var{val}, as per
@code{let}.  The binding operations occur in sequence from left to right.
The last expression of @var{body} must be a monadic expression, and its
result will become the result of the @code{mlet} or @code{mlet*} when run in
the @var{monad}.

@code{mlet*} is to @code{mlet} what @code{let*} is to @code{let}
(@pxref{Local Bindings,,, guile, GNU Guile Reference Manual}).
@end deffn

@deffn {Scheme System} mbegin @var{monad} @var{mexp} ...
Bind @var{mexp} and the following monadic expressions in sequence, returning
the result of the last expression.  Every expression in the sequence must be
a monadic expression.

This is akin to @code{mlet}, except that the return values of the monadic
expressions are ignored.  In that sense, it is analogous to @code{begin},
but applied to monadic expressions.
@end deffn

@deffn {Scheme System} mwhen @var{condition} @var{mexp0} @var{mexp*} ...
When @var{condition} is true, evaluate the sequence of monadic expressions
@var{mexp0}..@var{mexp*} as in an @code{mbegin}.  When @var{condition} is
false, return @code{*unspecified*} in the current monad.  Every expression
in the sequence must be a monadic expression.
@end deffn

@deffn {Scheme System} munless @var{condition} @var{mexp0} @var{mexp*} ...
When @var{condition} is false, evaluate the sequence of monadic expressions
@var{mexp0}..@var{mexp*} as in an @code{mbegin}.  When @var{condition} is
true, return @code{*unspecified*} in the current monad.  Every expression in
the sequence must be a monadic expression.
@end deffn

@cindex state monad
The @code{(guix monads)} module provides the @dfn{state monad}, which allows
an additional value---the state---to be @emph{threaded} through monadic
procedure calls.

@defvr {Scheme Variable} %state-monad
The state monad.  Procedures in the state monad can access and change the
state that is threaded.

Consider the example below.  The @code{square} procedure returns a value in
the state monad.  It returns the square of its argument, but also increments
the current state value:

@example
(define (square x)
  (mlet %state-monad ((count (current-state)))
    (mbegin %state-monad
      (set-current-state (+ 1 count))
      (return (* x x)))))

(run-with-state (sequence %state-monad (map square (iota 3))) 0)
@result{} (0 1 4)
@result{} 3
@end example

When ``run'' through @var{%state-monad}, we obtain that additional state
value, which is the number of @code{square} calls.
@end defvr

@deffn {Monadic Procedure} current-state
Return the current state as a monadic value.
@end deffn

@deffn {Monadic Procedure} set-current-state @var{value}
Set the current state to @var{value} and return the previous state as a
monadic value.
@end deffn

@deffn {Monadic Procedure} state-push @var{value}
Push @var{value} to the current state, which is assumed to be a list, and
return the previous state as a monadic value.
@end deffn

@deffn {Monadic Procedure} state-pop
Pop a value from the current state and return it as a monadic value.  The
state is assumed to be a list.
@end deffn

@deffn {Scheme Procedure} run-with-state @var{mval} [@var{state}]
Run monadic value @var{mval} starting with @var{state} as the initial
state.  Return two values: the resulting value, and the resulting state.
@end deffn

The main interface to the store monad, provided by the @code{(guix store)}
module, is as follows.

@defvr {Scheme Variable} %store-monad
The store monad---an alias for @var{%state-monad}.

Values in the store monad encapsulate accesses to the store.  When its
effect is needed, a value of the store monad must be ``evaluated'' by
passing it to the @code{run-with-store} procedure (see below.)
@end defvr

@deffn {Scheme Procedure} run-with-store @var{store} @var{mval} [#:guile-for-build] [#:system (%current-system)]
Run @var{mval}, a monadic value in the store monad, in @var{store}, an open
store connection.
@end deffn

@deffn {Monadic Procedure} text-file @var{name} @var{text} [@var{references}]
Return as a monadic value the absolute file name in the store of the file
containing @var{text}, a string.  @var{references} is a list of store items
that the resulting text file refers to; it defaults to the empty list.
@end deffn

@deffn {Monadic Procedure} binary-file @var{name} @var{data} [@var{references}]
Return as a monadic value the absolute file name in the store of the file
containing @var{data}, a bytevector.  @var{references} is a list of store
items that the resulting binary file refers to; it defaults to the empty
list.
@end deffn

@deffn {Monadic Procedure} interned-file @var{file} [@var{name}] @
         [#:recursive? #t] [#:select? (const #t)] Return the name of @var{file} once
interned in the store.  Use @var{name} as its store name, or the basename of
@var{file} if @var{name} is omitted.

When @var{recursive?} is true, the contents of @var{file} are added
recursively; if @var{file} designates a flat file and @var{recursive?} is
true, its contents are added, and its permission bits are kept.

When @var{recursive?} is true, call @code{(@var{select?} @var{file}
@var{stat})} for each directory entry, where @var{file} is the entry's
absolute file name and @var{stat} is the result of @code{lstat}; exclude
entries for which @var{select?} does not return true.

The example below adds a file to the store, under two different names:

@example
(run-with-store (open-connection)
  (mlet %store-monad ((a (interned-file "README"))
                      (b (interned-file "README" "LEGU-MIN")))
    (return (list a b))))

@result{} ("/gnu/store/rwm@dots{}-README" "/gnu/store/44i@dots{}-LEGU-MIN")
@end example

@end deffn

The @code{(guix packages)} module exports the following package-related
monadic procedures:

@deffn {Monadic Procedure} package-file @var{package} [@var{file}] @
       [#:system (%current-system)] [#:target #f] @ [#:output "out"] Return as a
monadic value in the absolute file name of @var{file} within the
@var{output} directory of @var{package}.  When @var{file} is omitted, return
the name of the @var{output} directory of @var{package}.  When @var{target}
is true, use it as a cross-compilation target triplet.
@end deffn

@deffn {Monadic Procedure} package->derivation @var{package} [@var{system}]
@deffnx {Monadic Procedure} package->cross-derivation @var{package} @
          @var{target} [@var{system}] Monadic version of @code{package-derivation} and
@code{package-cross-derivation} (@pxref{Pakete definieren}).
@end deffn


@node G-Ausdrücke
@section G-Ausdrücke

@cindex G-expression
@cindex build code quoting
So we have ``derivations'', which represent a sequence of build actions to
be performed to produce an item in the store (@pxref{Ableitungen}).  These
build actions are performed when asking the daemon to actually build the
derivations; they are run by the daemon in a container (@pxref{Aufruf des guix-daemon}).

@cindex strata of code
It should come as no surprise that we like to write these build actions in
Scheme.  When we do that, we end up with two @dfn{strata} of Scheme
code@footnote{The term @dfn{stratum} in this context was coined by Manuel
Serrano et al.@: in the context of their work on Hop.  Oleg Kiselyov, who
has written insightful
@url{http://okmij.org/ftp/meta-programming/#meta-scheme, essays and code on
this topic}, refers to this kind of code generation as @dfn{staging}.}: the
``host code''---code that defines packages, talks to the daemon, etc.---and
the ``build code''---code that actually performs build actions, such as
making directories, invoking @command{make}, etc.

To describe a derivation and its build actions, one typically needs to embed
build code inside host code.  It boils down to manipulating build code as
data, and the homoiconicity of Scheme---code has a direct representation as
data---comes in handy for that.  But we need more than the normal
@code{quasiquote} mechanism in Scheme to construct build expressions.

The @code{(guix gexp)} module implements @dfn{G-expressions}, a form of
S-expressions adapted to build expressions.  G-expressions, or @dfn{gexps},
consist essentially of three syntactic forms: @code{gexp}, @code{ungexp},
and @code{ungexp-splicing} (or simply: @code{#~}, @code{#$}, and
@code{#$@@}), which are comparable to @code{quasiquote}, @code{unquote}, and
@code{unquote-splicing}, respectively (@pxref{Expression Syntax,
@code{quasiquote},, guile, GNU Guile Reference Manual}).  However, there are
major differences:

@itemize
@item
Gexps are meant to be written to a file and run or manipulated by other
processes.

@item
When a high-level object such as a package or derivation is unquoted inside
a gexp, the result is as if its output file name had been introduced.

@item
Gexps carry information about the packages or derivations they refer to, and
these dependencies are automatically added as inputs to the build processes
that use them.
@end itemize

@cindex lowering, of high-level objects in gexps
This mechanism is not limited to package and derivation objects:
@dfn{compilers} able to ``lower'' other high-level objects to derivations or
files in the store can be defined, such that these objects can also be
inserted into gexps.  For example, a useful type of high-level objects that
can be inserted in a gexp is ``file-like objects'', which make it easy to
add files to the store and to refer to them in derivations and such (see
@code{local-file} and @code{plain-file} below.)

To illustrate the idea, here is an example of a gexp:

@example
(define build-exp
  #~(begin
      (mkdir #$output)
      (chdir #$output)
      (symlink (string-append #$coreutils "/bin/ls")
               "list-files")))
@end example

This gexp can be passed to @code{gexp->derivation}; we obtain a derivation
that builds a directory containing exactly one symlink to
@file{/gnu/store/@dots{}-coreutils-8.22/bin/ls}:

@example
(gexp->derivation "the-thing" build-exp)
@end example

As one would expect, the @code{"/gnu/store/@dots{}-coreutils-8.22"} string
is substituted to the reference to the @var{coreutils} package in the actual
build code, and @var{coreutils} is automatically made an input to the
derivation.  Likewise, @code{#$output} (equivalent to @code{(ungexp
output)}) is replaced by a string containing the directory name of the
output of the derivation.

@cindex cross compilation
In a cross-compilation context, it is useful to distinguish between
references to the @emph{native} build of a package---that can run on the
host---versus references to cross builds of a package.  To that end, the
@code{#+} plays the same role as @code{#$}, but is a reference to a native
package build:

@example
(gexp->derivation "vi"
   #~(begin
       (mkdir #$output)
       (system* (string-append #+coreutils "/bin/ln")
                "-s"
                (string-append #$emacs "/bin/emacs")
                (string-append #$output "/bin/vi")))
   #:target "mips64el-linux-gnu")
@end example

@noindent
In the example above, the native build of @var{coreutils} is used, so that
@command{ln} can actually run on the host; but then the cross-compiled build
of @var{emacs} is referenced.

@cindex imported modules, for gexps
@findex with-imported-modules
Another gexp feature is @dfn{imported modules}: sometimes you want to be
able to use certain Guile modules from the ``host environment'' in the gexp,
so those modules should be imported in the ``build environment''.  The
@code{with-imported-modules} form allows you to express that:

@example
(let ((build (with-imported-modules '((guix build utils))
               #~(begin
                   (use-modules (guix build utils))
                   (mkdir-p (string-append #$output "/bin"))))))
  (gexp->derivation "empty-dir"
                    #~(begin
                        #$build
                        (display "success!\n")
                        #t)))
@end example

@noindent
In this example, the @code{(guix build utils)} module is automatically
pulled into the isolated build environment of our gexp, such that
@code{(use-modules (guix build utils))} works as expected.

@cindex module closure
@findex source-module-closure
Usually you want the @emph{closure} of the module to be imported---i.e., the
module itself and all the modules it depends on---rather than just the
module; failing to do that, attempts to use the module will fail because of
missing dependent modules.  The @code{source-module-closure} procedure
computes the closure of a module by looking at its source file headers,
which comes in handy in this case:

@example
(use-modules (guix modules))   ;for 'source-module-closure'

(with-imported-modules (source-module-closure
                         '((guix build utils)
                           (gnu build vm)))
  (gexp->derivation "something-with-vms"
                    #~(begin
                        (use-modules (guix build utils)
                                     (gnu build vm))
                        @dots{})))
@end example

@cindex extensions, for gexps
@findex with-extensions
In the same vein, sometimes you want to import not just pure-Scheme modules,
but also ``extensions'' such as Guile bindings to C libraries or other
``full-blown'' packages.  Say you need the @code{guile-json} package
available on the build side, here's how you would do it:

@example
(use-modules (gnu packages guile))  ;for 'guile-json'

(with-extensions (list guile-json)
  (gexp->derivation "something-with-json"
                    #~(begin
                        (use-modules (json))
                        @dots{})))
@end example

The syntactic form to construct gexps is summarized below.

@deffn {Scheme Syntax} #~@var{exp}
@deffnx {Scheme Syntax} (gexp @var{exp})
Return a G-expression containing @var{exp}.  @var{exp} may contain one or
more of the following forms:

@table @code
@item #$@var{obj}
@itemx (ungexp @var{obj})
Introduce a reference to @var{obj}.  @var{obj} may have one of the supported
types, for example a package or a derivation, in which case the
@code{ungexp} form is replaced by its output file name---e.g.,
@code{"/gnu/store/@dots{}-coreutils-8.22}.

If @var{obj} is a list, it is traversed and references to supported objects
are substituted similarly.

If @var{obj} is another gexp, its contents are inserted and its dependencies
are added to those of the containing gexp.

If @var{obj} is another kind of object, it is inserted as is.

@item #$@var{obj}:@var{output}
@itemx (ungexp @var{obj} @var{output})
This is like the form above, but referring explicitly to the @var{output} of
@var{obj}---this is useful when @var{obj} produces multiple outputs
(@pxref{Pakete mit mehreren Ausgaben.}).

@item #+@var{obj}
@itemx #+@var{obj}:output
@itemx (ungexp-native @var{obj})
@itemx (ungexp-native @var{obj} @var{output})
Same as @code{ungexp}, but produces a reference to the @emph{native} build
of @var{obj} when used in a cross compilation context.

@item #$output[:@var{output}]
@itemx (ungexp output [@var{output}])
Insert a reference to derivation output @var{output}, or to the main output
when @var{output} is omitted.

This only makes sense for gexps passed to @code{gexp->derivation}.

@item #$@@@var{lst}
@itemx (ungexp-splicing @var{lst})
Like the above, but splices the contents of @var{lst} inside the containing
list.

@item #+@@@var{lst}
@itemx (ungexp-native-splicing @var{lst})
Like the above, but refers to native builds of the objects listed in
@var{lst}.

@end table

G-expressions created by @code{gexp} or @code{#~} are run-time objects of
the @code{gexp?} type (see below.)
@end deffn

@deffn {Scheme Syntax} with-imported-modules @var{modules} @var{body}@dots{}
Mark the gexps defined in @var{body}@dots{} as requiring @var{modules} in
their execution environment.

Each item in @var{modules} can be the name of a module, such as @code{(guix
build utils)}, or it can be a module name, followed by an arrow, followed by
a file-like object:

@example
`((guix build utils)
  (guix gcrypt)
  ((guix config) => ,(scheme-file "config.scm"
                                  #~(define-module @dots{}))))
@end example

@noindent
In the example above, the first two modules are taken from the search path,
and the last one is created from the given file-like object.

This form has @emph{lexical} scope: it has an effect on the gexps directly
defined in @var{body}@dots{}, but not on those defined, say, in procedures
called from @var{body}@dots{}.
@end deffn

@deffn {Scheme Syntax} with-extensions @var{extensions} @var{body}@dots{}
Mark the gexps defined in @var{body}@dots{} as requiring @var{extensions} in
their build and execution environment.  @var{extensions} is typically a list
of package objects such as those defined in the @code{(gnu packages guile)}
module.

Concretely, the packages listed in @var{extensions} are added to the load
path while compiling imported modules in @var{body}@dots{}; they are also
added to the load path of the gexp returned by @var{body}@dots{}.
@end deffn

@deffn {Scheme Procedure} gexp? @var{obj}
Return @code{#t} if @var{obj} is a G-expression.
@end deffn

G-expressions are meant to be written to disk, either as code building some
derivation, or as plain files in the store.  The monadic procedures below
allow you to do that (@pxref{Die Store-Monade}, for more information about
monads.)

@deffn {Monadic Procedure} gexp->derivation @var{name} @var{exp} @
       [#:system (%current-system)] [#:target #f] [#:graft? #t] @ [#:hash #f]
[#:hash-algo #f] @ [#:recursive? #f] [#:env-vars '()] [#:modules '()] @
[#:module-path @var{%load-path}] @ [#:effective-version "2.2"] @
[#:references-graphs #f] [#:allowed-references #f] @
[#:disallowed-references #f] @ [#:leaked-env-vars #f] @ [#:script-name
(string-append @var{name} "-builder")] @ [#:deprecation-warnings #f] @
[#:local-build? #f] [#:substitutable? #t] [#:guile-for-build #f] Return a
derivation @var{name} that runs @var{exp} (a gexp) with
@var{guile-for-build} (a derivation) on @var{system}; @var{exp} is stored in
a file called @var{script-name}.  When @var{target} is true, it is used as
the cross-compilation target triplet for packages referred to by @var{exp}.

@var{modules} is deprecated in favor of @code{with-imported-modules}.  Its
meaning is to make @var{modules} available in the evaluation context of
@var{exp}; @var{modules} is a list of names of Guile modules searched in
@var{module-path} to be copied in the store, compiled, and made available in
the load path during the execution of @var{exp}---e.g., @code{((guix build
utils) (guix build gnu-build-system))}.

@var{effective-version} determines the string to use when adding extensions
of @var{exp} (see @code{with-extensions}) to the search path---e.g.,
@code{"2.2"}.

@var{graft?} determines whether packages referred to by @var{exp} should be
grafted when applicable.

When @var{references-graphs} is true, it must be a list of tuples of one of
the following forms:

@example
(@var{file-name} @var{package})
(@var{file-name} @var{package} @var{output})
(@var{file-name} @var{derivation})
(@var{file-name} @var{derivation} @var{output})
(@var{file-name} @var{store-item})
@end example

The right-hand-side of each element of @var{references-graphs} is
automatically made an input of the build process of @var{exp}.  In the build
environment, each @var{file-name} contains the reference graph of the
corresponding item, in a simple text format.

@var{allowed-references} must be either @code{#f} or a list of output names
and packages.  In the latter case, the list denotes store items that the
result is allowed to refer to.  Any reference to another store item will
lead to a build error.  Similarly for @var{disallowed-references}, which can
list items that must not be referenced by the outputs.

@var{deprecation-warnings} determines whether to show deprecation warnings
while compiling modules.  It can be @code{#f}, @code{#t}, or
@code{'detailed}.

The other arguments are as for @code{derivation} (@pxref{Ableitungen}).
@end deffn

@cindex file-like objects
The @code{local-file}, @code{plain-file}, @code{computed-file},
@code{program-file}, and @code{scheme-file} procedures below return
@dfn{file-like objects}.  That is, when unquoted in a G-expression, these
objects lead to a file in the store.  Consider this G-expression:

@example
#~(system* #$(file-append glibc "/sbin/nscd") "-f"
           #$(local-file "/tmp/my-nscd.conf"))
@end example

The effect here is to ``intern'' @file{/tmp/my-nscd.conf} by copying it to
the store.  Once expanded, for instance @i{via} @code{gexp->derivation}, the
G-expression refers to that copy under @file{/gnu/store}; thus, modifying or
removing the file in @file{/tmp} does not have any effect on what the
G-expression does.  @code{plain-file} can be used similarly; it differs in
that the file content is directly passed as a string.

@deffn {Scheme Procedure} local-file @var{file} [@var{name}] @
   [#:recursive? #f] [#:select? (const #t)] Return an object representing local
file @var{file} to add to the store; this object can be used in a gexp.  If
@var{file} is a relative file name, it is looked up relative to the source
file where this form appears.  @var{file} will be added to the store under
@var{name}--by default the base name of @var{file}.

When @var{recursive?} is true, the contents of @var{file} are added
recursively; if @var{file} designates a flat file and @var{recursive?} is
true, its contents are added, and its permission bits are kept.

When @var{recursive?} is true, call @code{(@var{select?} @var{file}
@var{stat})} for each directory entry, where @var{file} is the entry's
absolute file name and @var{stat} is the result of @code{lstat}; exclude
entries for which @var{select?} does not return true.

This is the declarative counterpart of the @code{interned-file} monadic
procedure (@pxref{Die Store-Monade, @code{interned-file}}).
@end deffn

@deffn {Scheme Procedure} plain-file @var{name} @var{content}
Return an object representing a text file called @var{name} with the given
@var{content} (a string or a bytevector) to be added to the store.

This is the declarative counterpart of @code{text-file}.
@end deffn

@deffn {Scheme Procedure} computed-file @var{name} @var{gexp} @
          [#:options '(#:local-build? #t)] Return an object representing the store
item @var{name}, a file or directory computed by @var{gexp}.  @var{options}
is a list of additional arguments to pass to @code{gexp->derivation}.

This is the declarative counterpart of @code{gexp->derivation}.
@end deffn

@deffn {Monadic Procedure} gexp->script @var{name} @var{exp} @
  [#:guile (default-guile)] [#:module-path %load-path] Return an executable
script @var{name} that runs @var{exp} using @var{guile}, with @var{exp}'s
imported modules in its search path.  Look up @var{exp}'s modules in
@var{module-path}.

The example below builds a script that simply invokes the @command{ls}
command:

@example
(use-modules (guix gexp) (gnu packages base))

(gexp->script "list-files"
              #~(execl #$(file-append coreutils "/bin/ls")
                       "ls"))
@end example

When ``running'' it through the store (@pxref{Die Store-Monade,
@code{run-with-store}}), we obtain a derivation that produces an executable
file @file{/gnu/store/@dots{}-list-files} along these lines:

@example
#!/gnu/store/@dots{}-guile-2.0.11/bin/guile -ds
!#
(execl "/gnu/store/@dots{}-coreutils-8.22"/bin/ls" "ls")
@end example
@end deffn

@deffn {Scheme Procedure} program-file @var{name} @var{exp} @
          [#:guile #f] [#:module-path %load-path] Return an object representing the
executable store item @var{name} that runs @var{gexp}.  @var{guile} is the
Guile package used to execute that script.  Imported modules of @var{gexp}
are looked up in @var{module-path}.

This is the declarative counterpart of @code{gexp->script}.
@end deffn

@deffn {Monadic Procedure} gexp->file @var{name} @var{exp} @
            [#:set-load-path? #t] [#:module-path %load-path] @ [#:splice? #f] @ [#:guile
(default-guile)] Return a derivation that builds a file @var{name}
containing @var{exp}.  When @var{splice?} is true, @var{exp} is considered
to be a list of expressions that will be spliced in the resulting file.

When @var{set-load-path?} is true, emit code in the resulting file to set
@code{%load-path} and @code{%load-compiled-path} to honor @var{exp}'s
imported modules.  Look up @var{exp}'s modules in @var{module-path}.

The resulting file holds references to all the dependencies of @var{exp} or
a subset thereof.
@end deffn

@deffn {Scheme Procedure} scheme-file @var{name} @var{exp} [#:splice? #f]
Return an object representing the Scheme file @var{name} that contains
@var{exp}.

This is the declarative counterpart of @code{gexp->file}.
@end deffn

@deffn {Monadic Procedure} text-file* @var{name} @var{text} @dots{}
Return as a monadic value a derivation that builds a text file containing
all of @var{text}.  @var{text} may list, in addition to strings, objects of
any type that can be used in a gexp: packages, derivations, local file
objects, etc.  The resulting store file holds references to all these.

This variant should be preferred over @code{text-file} anytime the file to
create will reference items from the store.  This is typically the case when
building a configuration file that embeds store file names, like this:

@example
(define (profile.sh)
  ;; Return the name of a shell script in the store that
  ;; initializes the 'PATH' environment variable.
  (text-file* "profile.sh"
              "export PATH=" coreutils "/bin:"
              grep "/bin:" sed "/bin\n"))
@end example

In this example, the resulting @file{/gnu/store/@dots{}-profile.sh} file
will reference @var{coreutils}, @var{grep}, and @var{sed}, thereby
preventing them from being garbage-collected during its lifetime.
@end deffn

@deffn {Scheme Procedure} mixed-text-file @var{name} @var{text} @dots{}
Return an object representing store file @var{name} containing @var{text}.
@var{text} is a sequence of strings and file-like objects, as in:

@example
(mixed-text-file "profile"
                 "export PATH=" coreutils "/bin:" grep "/bin")
@end example

This is the declarative counterpart of @code{text-file*}.
@end deffn

@deffn {Scheme Procedure} file-union @var{name} @var{files}
Return a @code{<computed-file>} that builds a directory containing all of
@var{files}.  Each item in @var{files} must be a two-element list where the
first element is the file name to use in the new directory, and the second
element is a gexp denoting the target file.  Here's an example:

@example
(file-union "etc"
            `(("hosts" ,(plain-file "hosts"
                                    "127.0.0.1 localhost"))
              ("bashrc" ,(plain-file "bashrc"
                                     "alias ls='ls --color=auto'"))))
@end example

This yields an @code{etc} directory containing these two files.
@end deffn

@deffn {Scheme Procedure} directory-union @var{name} @var{things}
Return a directory that is the union of @var{things}, where @var{things} is
a list of file-like objects denoting directories.  For example:

@example
(directory-union "guile+emacs" (list guile emacs))
@end example

yields a directory that is the union of the @code{guile} and @code{emacs}
packages.
@end deffn

@deffn {Scheme Procedure} file-append @var{obj} @var{suffix} @dots{}
Return a file-like object that expands to the concatenation of @var{obj} and
@var{suffix}, where @var{obj} is a lowerable object and each @var{suffix} is
a string.

As an example, consider this gexp:

@example
(gexp->script "run-uname"
              #~(system* #$(file-append coreutils
                                        "/bin/uname")))
@end example

The same effect could be achieved with:

@example
(gexp->script "run-uname"
              #~(system* (string-append #$coreutils
                                        "/bin/uname")))
@end example

There is one difference though: in the @code{file-append} case, the
resulting script contains the absolute file name as a string, whereas in the
second case, the resulting script contains a @code{(string-append @dots{})}
expression to construct the file name @emph{at run time}.
@end deffn


Of course, in addition to gexps embedded in ``host'' code, there are also
modules containing build tools.  To make it clear that they are meant to be
used in the build stratum, these modules are kept in the @code{(guix build
@dots{})} name space.

@cindex lowering, of high-level objects in gexps
Internally, high-level objects are @dfn{lowered}, using their compiler, to
either derivations or store items.  For instance, lowering a package yields
a derivation, and lowering a @code{plain-file} yields a store item.  This is
achieved using the @code{lower-object} monadic procedure.

@deffn {Monadic Procedure} lower-object @var{obj} [@var{system}] @
           [#:target #f] Return as a value in @var{%store-monad} the derivation or
store item corresponding to @var{obj} for @var{system}, cross-compiling for
@var{target} if @var{target} is true.  @var{obj} must be an object that has
an associated gexp compiler, such as a @code{<package>}.
@end deffn

@node Invoking guix repl
@section Invoking @command{guix repl}

@cindex REPL, read-eval-print loop
The @command{guix repl} command spawns a Guile @dfn{read-eval-print loop}
(REPL) for interactive programming (@pxref{Using Guile Interactively,,,
guile, GNU Guile Reference Manual}).  Compared to just launching the
@command{guile} command, @command{guix repl} guarantees that all the Guix
modules and all its dependencies are available in the search path.  You can
use it this way:

@example
$ guix repl
scheme@@(guile-user)> ,use (gnu packages base)
scheme@@(guile-user)> coreutils
$1 = #<package coreutils@@8.29 gnu/packages/base.scm:327 3e28300>
@end example

@cindex inferiors
In addition, @command{guix repl} implements a simple machine-readable REPL
protocol for use by @code{(guix inferior)}, a facility to interact with
@dfn{inferiors}, separate processes running a potentially different revision
of Guix.

The available options are as follows:

@table @code
@item --type=@var{type}
@itemx -t @var{type}
Start a REPL of the given @var{TYPE}, which can be one of the following:

@table @code
@item guile
This is default, and it spawns a standard full-featured Guile REPL.
@item machine
Spawn a REPL that uses the machine-readable protocol.  This is the protocol
that the @code{(guix inferior)} module speaks.
@end table

@item --listen=@var{Endpunkt}
By default, @command{guix repl} reads from standard input and writes to
standard output.  When this option is passed, it will instead listen for
connections on @var{endpoint}.  Here are examples of valid options:

@table @code
@item --listen=tcp:37146
Accept connections on localhost on port 37146.

@item --listen=unix:/tmp/socket
Accept connections on the Unix-domain socket @file{/tmp/socket}.
@end table
@end table

@c *********************************************************************
@node Zubehör
@chapter Zubehör

This section describes Guix command-line utilities.  Some of them are
primarily targeted at developers and users who write new package
definitions, while others are more generally useful.  They complement the
Scheme programming interface of Guix in a convenient way.

@menu
* Aufruf von guix build::    Pakete aus der Befehlszeile heraus erstellen.
* Aufruf von guix edit::     Paketdefinitionen bearbeiten.
* Aufruf von guix download::  Herunterladen einer Datei und Ausgabe ihres 
                                Hashes.
* Aufruf von guix hash::     Den kryptographischen Hash einer Datei 
                               berechnen.
* Aufruf von guix import::   Paketdefinitionen importieren.
* Aufruf von guix refresh::  Paketdefinitionen aktualisieren.
* Aufruf von guix lint::     Fehler in Paketdefinitionen finden.
* Aufruf von guix size::     Plattenverbrauch profilieren.
* Aufruf von guix graph::    Den Paketgraphen visualisieren.
* Aufruf von guix environment::  Entwicklungsumgebungen einrichten.
* Aufruf von guix publish::  Substitute teilen.
* Aufruf von guix challenge::  Die Substitut-Server anfechten.
* Aufruf von guix copy::     Mit einem entfernten Store Dateien austauschen.
* Aufruf von guix container::  Prozesse isolieren.
* Aufruf von guix weather::  Die Verfügbarkeit von Substituten 
                               einschätzen.
* Invoking guix processes::  Listing client processes.
@end menu

@node Aufruf von guix build
@section Aufruf von @command{guix build}

@cindex package building
@cindex @command{guix build}
The @command{guix build} command builds packages or derivations and their
dependencies, and prints the resulting store paths.  Note that it does not
modify the user's profile---this is the job of the @command{guix package}
command (@pxref{Aufruf von guix package}).  Thus, it is mainly useful for
distribution developers.

The general syntax is:

@example
guix build @var{options} @var{package-or-derivation}@dots{}
@end example

As an example, the following command builds the latest versions of Emacs and
of Guile, displays their build logs, and finally displays the resulting
directories:

@example
guix build emacs guile
@end example

Similarly, the following command builds all the available packages:

@example
guix build --quiet --keep-going \
  `guix package -A | cut -f1,2 --output-delimiter=@@`
@end example

@var{package-or-derivation} may be either the name of a package found in the
software distribution such as @code{coreutils} or @code{coreutils@@8.20}, or
a derivation such as @file{/gnu/store/@dots{}-coreutils-8.19.drv}.  In the
former case, a package with the corresponding name (and optionally version)
is searched for among the GNU distribution modules (@pxref{Paketmodule}).

Alternatively, the @code{--expression} option may be used to specify a
Scheme expression that evaluates to a package; this is useful when
disambiguating among several same-named packages or package variants is
needed.

There may be zero or more @var{options}.  The available options are
described in the subsections below.

@menu
* Gemeinsame Erstellungsoptionen::  Erstellungsoptionen für die meisten 
                                      Befehle.
* Paketumwandlungsoptionen::  Varianten von Paketen erzeugen.
* Zusätzliche Erstellungsoptionen::  Optionen spezifisch für »guix 
                                        build«.
* Fehlschläge beim Erstellen untersuchen::  Praxiserfahrung bei der 
                                               Paketerstellung.
@end menu

@node Gemeinsame Erstellungsoptionen
@subsection Gemeinsame Erstellungsoptionen

A number of options that control the build process are common to
@command{guix build} and other commands that can spawn builds, such as
@command{guix package} or @command{guix archive}.  These are the following:

@table @code

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{Paketmodule}).

This allows users to define their own packages and make them visible to the
command-line tools.

@item --keep-failed
@itemx -K
Keep the build tree of failed builds.  Thus, if a build fails, its build
tree is kept under @file{/tmp}, in a directory whose name is shown at the
end of the build log.  This is useful when debugging build issues.
@xref{Fehlschläge beim Erstellen untersuchen}, for tips and tricks on how to debug build
issues.

@item --keep-going
@itemx -k
Keep going when some of the derivations fail to build; return only once all
the builds have either completed or failed.

The default behavior is to stop as soon as one of the specified derivations
has failed.

@item --dry-run
@itemx -n
Do not build the derivations.

@anchor{fallback-option}
@item --fallback
When substituting a pre-built binary fails, fall back to building packages
locally (@pxref{Fehler bei der Substitution}).

@item --substitute-urls=@var{URLs}
@anchor{client-substitute-urls}
Consider @var{urls} the whitespace-separated list of substitute source URLs,
overriding the default list of URLs of @command{guix-daemon}
(@pxref{daemon-substitute-urls,, @command{guix-daemon} URLs}).

This means that substitutes may be downloaded from @var{urls}, provided they
are signed by a key authorized by the system administrator
(@pxref{Substitute}).

When @var{urls} is the empty string, substitutes are effectively disabled.

@item --no-substitutes
Benutze keine Substitute für Erstellungsergebnisse. Das heißt, dass alle
Objekte lokal erstellt werden müssen, und kein Herunterladen von vorab
erstellten Binärdateien erlaubt ist (@pxref{Substitute}).

@item --no-grafts
Do not ``graft'' packages.  In practice, this means that package updates
available as grafts are not applied.  @xref{Sicherheitsaktualisierungen}, for more
information on grafts.

@item --rounds=@var{n}
Build each derivation @var{n} times in a row, and raise an error if
consecutive build results are not bit-for-bit identical.

This is a useful way to detect non-deterministic builds processes.
Non-deterministic build processes are a problem because they make it
practically impossible for users to @emph{verify} whether third-party
binaries are genuine.  @xref{Aufruf von guix challenge}, for more.

Note that, currently, the differing build results are not kept around, so
you will have to manually investigate in case of an error---e.g., by
stashing one of the build results with @code{guix archive --export}
(@pxref{Aufruf von guix archive}), then rebuilding, and finally comparing the
two results.

@item --no-build-hook
Nicht versuchen, Erstellungen über den »Build-Hook« des Daemons auszulagern
(@pxref{Auslagern des Daemons einrichten}). Somit wird lokal erstellt, statt
Erstellungen auf entfernte Maschinen auszulagern.

@item --max-silent-time=@var{Sekunden}
Wenn der Erstellungs- oder Substitutionsprozess länger als
@var{Sekunden}-lang keine Ausgabe erzeugt, wird er abgebrochen und ein
Fehler beim Erstellen gemeldet.

By default, the daemon's setting is honored (@pxref{Aufruf des guix-daemon,
@code{--max-silent-time}}).

@item --timeout=@var{Sekunden}
Entsprechend wird hier der Erstellungs- oder Substitutionsprozess
abgebrochen und als Fehlschlag gemeldet, wenn er mehr als
@var{Sekunden}-lang dauert.

By default, the daemon's setting is honored (@pxref{Aufruf des guix-daemon,
@code{--timeout}}).

@item --verbosity=@var{level}
Use the given verbosity level.  @var{level} must be an integer between 0 and
5; higher means more verbose output.  Setting a level of 4 or more may be
helpful when debugging setup issues with the build daemon.

@item --cores=@var{n}
@itemx -c @var{n}
Allow the use of up to @var{n} CPU cores for the build.  The special value
@code{0} means to use as many CPU cores as available.

@item --max-jobs=@var{n}
@itemx -M @var{n}
Allow at most @var{n} build jobs in parallel.  @xref{Aufruf des guix-daemon,
@code{--max-jobs}}, for details about this option and the equivalent
@command{guix-daemon} option.

@end table

Behind the scenes, @command{guix build} is essentially an interface to the
@code{package-derivation} procedure of the @code{(guix packages)} module,
and to the @code{build-derivations} procedure of the @code{(guix
derivations)} module.

In addition to options explicitly passed on the command line, @command{guix
build} and other @command{guix} commands that support building honor the
@code{GUIX_BUILD_OPTIONS} environment variable.

@defvr {Environment Variable} GUIX_BUILD_OPTIONS
Users can define this variable to a list of command line options that will
automatically be used by @command{guix build} and other @command{guix}
commands that can perform builds, as in the example below:

@example
$ export GUIX_BUILD_OPTIONS="--no-substitutes -c 2 -L /foo/bar"
@end example

These options are parsed independently, and the result is appended to the
parsed command-line options.
@end defvr


@node Paketumwandlungsoptionen
@subsection Paketumwandlungsoptionen

@cindex package variants
Another set of command-line options supported by @command{guix build} and
also @command{guix package} are @dfn{package transformation options}.  These
are options that make it possible to define @dfn{package variants}---for
instance, packages built from different source code.  This is a convenient
way to create customized packages on the fly without having to type in the
definitions of package variants (@pxref{Pakete definieren}).

@table @code

@item --with-source=@var{source}
@itemx --with-source=@var{package}=@var{source}
@itemx --with-source=@var{package}@@@var{version}=@var{source}
Use @var{source} as the source of @var{package}, and @var{version} as its
version number.  @var{source} must be a file name or a URL, as for
@command{guix download} (@pxref{Aufruf von guix download}).

When @var{package} is omitted, it is taken to be the package name specified
on the command line that matches the base of @var{source}---e.g., if
@var{source} is @code{/src/guile-2.0.10.tar.gz}, the corresponding package
is @code{guile}.

Likewise, when @var{version} is omitted, the version string is inferred from
@var{source}; in the previous example, it is @code{2.0.10}.

This option allows users to try out versions of packages other than the one
provided by the distribution.  The example below downloads
@file{ed-1.7.tar.gz} from a GNU mirror and uses that as the source for the
@code{ed} package:

@example
guix build ed --with-source=mirror://gnu/ed/ed-1.7.tar.gz
@end example

As a developer, @code{--with-source} makes it easy to test release
candidates:

@example
guix build guile --with-source=../guile-2.0.9.219-e1bb7.tar.xz
@end example

@dots{} or to build from a checkout in a pristine environment:

@example
$ git clone git://git.sv.gnu.org/guix.git
$ guix build guix --with-source=guix@@1.0=./guix
@end example

@item --with-input=@var{package}=@var{replacement}
Replace dependency on @var{package} by a dependency on @var{replacement}.
@var{package} must be a package name, and @var{replacement} must be a
package specification such as @code{guile} or @code{guile@@1.8}.

For instance, the following command builds Guix, but replaces its dependency
on the current stable version of Guile with a dependency on the legacy
version of Guile, @code{guile@@2.0}:

@example
guix build --with-input=guile=guile@@2.0 guix
@end example

This is a recursive, deep replacement.  So in this example, both @code{guix}
and its dependency @code{guile-json} (which also depends on @code{guile})
get rebuilt against @code{guile@@2.0}.

This is implemented using the @code{package-input-rewriting} Scheme
procedure (@pxref{Pakete definieren, @code{package-input-rewriting}}).

@item --with-graft=@var{package}=@var{replacement}
This is similar to @code{--with-input} but with an important difference:
instead of rebuilding the whole dependency chain, @var{replacement} is built
and then @dfn{grafted} onto the binaries that were initially referring to
@var{package}.  @xref{Sicherheitsaktualisierungen}, for more information on grafts.

For example, the command below grafts version 3.5.4 of GnuTLS onto Wget and
all its dependencies, replacing references to the version of GnuTLS they
currently refer to:

@example
guix build --with-graft=gnutls=gnutls@@3.5.4 wget
@end example

This has the advantage of being much faster than rebuilding everything.  But
there is a caveat: it works if and only if @var{package} and
@var{replacement} are strictly compatible---for example, if they provide a
library, the application binary interface (ABI) of those libraries must be
compatible.  If @var{replacement} is somehow incompatible with
@var{package}, then the resulting package may be unusable.  Use with care!

@end table

@node Zusätzliche Erstellungsoptionen
@subsection Zusätzliche Erstellungsoptionen

The command-line options presented below are specific to @command{guix
build}.

@table @code

@item --quiet
@itemx -q
Build quietly, without displaying the build log.  Upon completion, the build
log is kept in @file{/var} (or similar) and can always be retrieved using
the @option{--log-file} option.

@item --file=@var{file}
@itemx -f @var{Datei}
Build the package, derivation, or other file-like object that the code
within @var{file} evaluates to (@pxref{G-Ausdrücke, file-like objects}).

As an example, @var{file} might contain a package definition like this
(@pxref{Pakete definieren}):

@example
@verbatiminclude package-hello.scm
@end example

@item --expression=@var{expr}
@itemx -e @var{expr}
Build the package or derivation @var{expr} evaluates to.

For example, @var{expr} may be @code{(@@ (gnu packages guile)  guile-1.8)},
which unambiguously designates this specific variant of version 1.8 of
Guile.

Alternatively, @var{expr} may be a G-expression, in which case it is used as
a build program passed to @code{gexp->derivation} (@pxref{G-Ausdrücke}).

Lastly, @var{expr} may refer to a zero-argument monadic procedure
(@pxref{Die Store-Monade}).  The procedure must return a derivation as a
monadic value, which is then passed through @code{run-with-store}.

@item --source
@itemx -S
Build the source derivations of the packages, rather than the packages
themselves.

For instance, @code{guix build -S gcc} returns something like
@file{/gnu/store/@dots{}-gcc-4.7.2.tar.bz2}, which is the GCC source
tarball.

The returned source tarball is the result of applying any patches and code
snippets specified in the package @code{origin} (@pxref{Pakete definieren}).

@item --sources
Fetch and return the source of @var{package-or-derivation} and all their
dependencies, recursively.  This is a handy way to obtain a local copy of
all the source code needed to build @var{packages}, allowing you to
eventually build them even without network access.  It is an extension of
the @code{--source} option and can accept one of the following optional
argument values:

@table @code
@item package
This value causes the @code{--sources} option to behave in the same way as
the @code{--source} option.

@item all
Build the source derivations of all packages, including any source that
might be listed as @code{inputs}.  This is the default value.

@example
$ guix build --sources tzdata
The following derivations will be built:
   /gnu/store/@dots{}-tzdata2015b.tar.gz.drv
   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv
@end example

@item transitive
Build the source derivations of all packages, as well of all transitive
inputs to the packages.  This can be used e.g. to prefetch package source
for later offline building.

@example
$ guix build --sources=transitive tzdata
The following derivations will be built:
   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv
   /gnu/store/@dots{}-findutils-4.4.2.tar.xz.drv
   /gnu/store/@dots{}-grep-2.21.tar.xz.drv
   /gnu/store/@dots{}-coreutils-8.23.tar.xz.drv
   /gnu/store/@dots{}-make-4.1.tar.xz.drv
   /gnu/store/@dots{}-bash-4.3.tar.xz.drv
@dots{}
@end example

@end table

@item --system=@var{System}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of the
system type of the build host.

@quotation Anmerkung
The @code{--system} flag is for @emph{native} compilation and must not be
confused with cross-compilation.  See @code{--target} below for information
on cross-compilation.
@end quotation

An example use of this is on Linux-based systems, which can emulate
different personalities.  For instance, passing @code{--system=i686-linux}
on an @code{x86_64-linux} system or @code{--system=armhf-linux} on an
@code{aarch64-linux} system allows you to build packages in a complete
32-bit environment.

@quotation Anmerkung
Building for an @code{armhf-linux} system is unconditionally enabled on
@code{aarch64-linux} machines, although certain aarch64 chipsets do not
allow for this functionality, notably the ThunderX.
@end quotation

Similarly, when transparent emulation with QEMU and @code{binfmt_misc} is
enabled (@pxref{Virtualisierungsdienste, @code{qemu-binfmt-service-type}}),
you can build for any system for which a QEMU @code{binfmt_misc} handler is
installed.

Builds for a system other than that of the machine you are using can also be
offloaded to a remote machine of the right architecture.  @xref{Auslagern des Daemons einrichten}, for more information on offloading.

@item --target=@var{triplet}
@cindex cross-compilation
Cross-build for @var{triplet}, which must be a valid GNU triplet, such as
@code{"mips64el-linux-gnu"} (@pxref{Specifying target triplets, GNU
configuration triplets,, autoconf, Autoconf}).

@anchor{build-check}
@item --check
@cindex determinism, checking
@cindex reproducibility, checking
Rebuild @var{package-or-derivation}, which are already available in the
store, and raise an error if the build results are not bit-for-bit
identical.

This mechanism allows you to check whether previously installed substitutes
are genuine (@pxref{Substitute}), or whether the build result of a package
is deterministic.  @xref{Aufruf von guix challenge}, for more background
information and tools.

Wenn dies zusammen mit @option{--keep-failed} benutzt wird, bleiben die sich
unterscheidenden Ausgaben im Store unter dem Namen
@file{/gnu/store/@dots{}-check}. Dadurch können Unterschiede zwischen den
beiden Ergebnissen leicht erkannt werden.

@item --repair
@cindex repairing store items
@cindex Datenbeschädigung, Behebung
Attempt to repair the specified store items, if they are corrupt, by
re-downloading or rebuilding them.

This operation is not atomic and thus restricted to @code{root}.

@item --derivations
@itemx -d
Return the derivation paths, not the output paths, of the given packages.

@item --root=@var{file}
@itemx -r @var{file}
@cindex GC roots, adding
@cindex garbage collector roots, adding
Make @var{file} a symlink to the result, and register it as a garbage
collector root.

Consequently, the results of this @command{guix build} invocation are
protected from garbage collection until @var{file} is removed.  When that
option is omitted, build results are eligible for garbage collection as soon
as the build completes.  @xref{Aufruf von guix gc}, for more on GC roots.

@item --log-file
@cindex build logs, access
Return the build log file names or URLs for the given
@var{package-or-derivation}, or raise an error if build logs are missing.

This works regardless of how packages or derivations are specified.  For
instance, the following invocations are equivalent:

@example
guix build --log-file `guix build -d guile`
guix build --log-file `guix build guile`
guix build --log-file guile
guix build --log-file -e '(@@ (gnu packages guile) guile-2.0)'
@end example

If a log is unavailable locally, and unless @code{--no-substitutes} is
passed, the command looks for a corresponding log on one of the substitute
servers (as specified with @code{--substitute-urls}.)

So for instance, imagine you want to see the build log of GDB on MIPS, but
you are actually on an @code{x86_64} machine:

@example
$ guix build --log-file gdb -s mips64el-linux
https://hydra.gnu.org/log/@dots{}-gdb-7.10
@end example

You can freely access a huge library of build logs!
@end table

@node Fehlschläge beim Erstellen untersuchen
@subsection Fehlschläge beim Erstellen untersuchen

@cindex build failures, debugging
When defining a new package (@pxref{Pakete definieren}), you will probably
find yourself spending some time debugging and tweaking the build until it
succeeds.  To do that, you need to operate the build commands yourself in an
environment as close as possible to the one the build daemon uses.

To that end, the first thing to do is to use the @option{--keep-failed} or
@option{-K} option of @command{guix build}, which will keep the failed build
tree in @file{/tmp} or whatever directory you specified as @code{TMPDIR}
(@pxref{Aufruf von guix build, @code{--keep-failed}}).

From there on, you can @command{cd} to the failed build tree and source the
@file{environment-variables} file, which contains all the environment
variable definitions that were in place when the build failed.  So let's say
you're debugging a build failure in package @code{foo}; a typical session
would look like this:

@example
$ guix build foo -K
@dots{} @i{build fails}
$ cd /tmp/guix-build-foo.drv-0
$ source ./environment-variables
$ cd foo-1.2
@end example

Now, you can invoke commands as if you were the daemon (almost) and
troubleshoot your build process.

Sometimes it happens that, for example, a package's tests pass when you run
them manually but they fail when the daemon runs them.  This can happen
because the daemon runs builds in containers where, unlike in our
environment above, network access is missing, @file{/bin/sh} does not exist,
etc. (@pxref{Einrichten der Erstellungsumgebung}).

In such cases, you may need to run inspect the build process from within a
container similar to the one the build daemon creates:

@example
$ guix build -K foo
@dots{}
$ cd /tmp/guix-build-foo.drv-0
$ guix environment --no-grafts -C foo --ad-hoc strace gdb
[env]# source ./environment-variables
[env]# cd foo-1.2
@end example

Here, @command{guix environment -C} creates a container and spawns a new
shell in it (@pxref{Aufruf von guix environment}).  The @command{--ad-hoc
strace gdb} part adds the @command{strace} and @command{gdb} commands to the
container, which would may find handy while debugging.  The
@option{--no-grafts} option makes sure we get the exact same environment,
with ungrafted packages (@pxref{Sicherheitsaktualisierungen}, for more info on grafts).

To get closer to a container like that used by the build daemon, we can
remove @file{/bin/sh}:

@example
[env]# rm /bin/sh
@end example

(Don't worry, this is harmless: this is all happening in the throw-away
container created by @command{guix environment}.)

The @command{strace} command is probably not in the search path, but we can
run:

@example
[env]# $GUIX_ENVIRONMENT/bin/strace -f -o log make check
@end example

In this way, not only you will have reproduced the environment variables the
daemon uses, you will also be running the build process in a container
similar to the one the daemon uses.


@node Aufruf von guix edit
@section Invoking @command{guix edit}

@cindex @command{guix edit}
@cindex package definition, editing
So many packages, so many source files! The @command{guix edit} command
facilitates the life of users and packagers by pointing their editor at the
source file containing the definition of the specified packages.  For
instance:

@example
guix edit gcc@@4.9 vim
@end example

@noindent
launches the program specified in the @code{VISUAL} or in the @code{EDITOR}
environment variable to view the recipe of GCC@tie{}4.9.3 and that of Vim.

If you are using a Guix Git checkout (@pxref{Erstellung aus dem Git}), or have
created your own packages on @code{GUIX_PACKAGE_PATH} (@pxref{Paketmodule}), you will be able to edit the package recipes.  In other cases,
you will be able to examine the read-only recipes for packages currently in
the store.


@node Aufruf von guix download
@section Invoking @command{guix download}

@cindex @command{guix download}
@cindex downloading package sources
When writing a package definition, developers typically need to download a
source tarball, compute its SHA256 hash, and write that hash in the package
definition (@pxref{Pakete definieren}).  The @command{guix download} tool
helps with this task: it downloads a file from the given URI, adds it to the
store, and prints both its file name in the store and its SHA256 hash.

The fact that the downloaded file is added to the store saves bandwidth:
when the developer eventually tries to build the newly defined package with
@command{guix build}, the source tarball will not have to be downloaded
again because it is already in the store.  It is also a convenient way to
temporarily stash files, which may be deleted eventually (@pxref{Aufruf von guix gc}).

The @command{guix download} command supports the same URIs as used in
package definitions.  In particular, it supports @code{mirror://} URIs.
@code{https} URIs (HTTP over TLS) are supported @emph{provided} the Guile
bindings for GnuTLS are available in the user's environment; when they are
not available, an error is raised.  @xref{Guile Preparations, how to install
the GnuTLS bindings for Guile,, gnutls-guile, GnuTLS-Guile}, for more
information.

@command{guix download} verifies HTTPS server certificates by loading the
certificates of X.509 authorities from the directory pointed to by the
@code{SSL_CERT_DIR} environment variable (@pxref{X.509-Zertifikate}),
unless @option{--no-check-certificate} is used.

The following options are available:

@table @code
@item --format=@var{fmt}
@itemx -f @var{fmt}
Write the hash in the format specified by @var{fmt}.  For more information
on the valid values for @var{fmt}, @pxref{Aufruf von guix hash}.

@item --no-check-certificate
Do not validate the X.509 certificates of HTTPS servers.

When using this option, you have @emph{absolutely no guarantee} that you are
communicating with the authentic server responsible for the given URL, which
makes you vulnerable to ``man-in-the-middle'' attacks.

@item --output=@var{file}
@itemx -o @var{file}
Save the downloaded file to @var{file} instead of adding it to the store.
@end table

@node Aufruf von guix hash
@section Invoking @command{guix hash}

@cindex @command{guix hash}
The @command{guix hash} command computes the SHA256 hash of a file.  It is
primarily a convenience tool for anyone contributing to the distribution: it
computes the cryptographic hash of a file, which can be used in the
definition of a package (@pxref{Pakete definieren}).

The general syntax is:

@example
guix hash @var{option} @var{file}
@end example

When @var{file} is @code{-} (a hyphen), @command{guix hash} computes the
hash of data read from standard input.  @command{guix hash} has the
following options:

@table @code

@item --format=@var{fmt}
@itemx -f @var{fmt}
Write the hash in the format specified by @var{fmt}.

Supported formats: @code{nix-base32}, @code{base32}, @code{base16}
(@code{hex} and @code{hexadecimal} can be used as well).

If the @option{--format} option is not specified, @command{guix hash} will
output the hash in @code{nix-base32}.  This representation is used in the
definitions of packages.

@item --recursive
@itemx -r
Compute the hash on @var{file} recursively.

@c FIXME: Replace xref above with xref to an ``Archive'' section when
@c it exists.
In this case, the hash is computed on an archive containing @var{file},
including its children if it is a directory.  Some of the metadata of
@var{file} is part of the archive; for instance, when @var{file} is a
regular file, the hash is different depending on whether @var{file} is
executable or not.  Metadata such as time stamps has no impact on the hash
(@pxref{Aufruf von guix archive}).

@item --exclude-vcs
@itemx -x
When combined with @option{--recursive}, exclude version control system
directories (@file{.bzr}, @file{.git}, @file{.hg}, etc.)

@vindex git-fetch
As an example, here is how you would compute the hash of a Git checkout,
which is useful when using the @code{git-fetch} method (@pxref{„origin“-Referenz}):

@example
$ git clone http://example.org/foo.git
$ cd foo
$ guix hash -rx .
@end example
@end table

@node Aufruf von guix import
@section Invoking @command{guix import}

@cindex importing packages
@cindex package import
@cindex package conversion
@cindex Invoking @command{guix import}
The @command{guix import} command is useful for people who would like to add
a package to the distribution with as little work as possible---a legitimate
demand.  The command knows of a few repositories from which it can
``import'' package metadata.  The result is a package definition, or a
template thereof, in the format we know (@pxref{Pakete definieren}).

The general syntax is:

@example
guix import @var{importer} @var{options}@dots{}
@end example

@var{importer} specifies the source from which to import package metadata,
and @var{options} specifies a package identifier and other options specific
to @var{importer}.  Currently, the available ``importers'' are:

@table @code
@item gnu
Import metadata for the given GNU package.  This provides a template for the
latest version of that GNU package, including the hash of its source
tarball, and its canonical synopsis and description.

Additional information such as the package dependencies and its license
needs to be figured out manually.

For example, the following command returns a package definition for
GNU@tie{}Hello:

@example
guix import gnu hello
@end example

Specific command-line options are:

@table @code
@item --key-download=@var{policy}
As for @code{guix refresh}, specify the policy to handle missing OpenPGP
keys when verifying the package signature.  @xref{Aufruf von guix refresh,
@code{--key-download}}.
@end table

@item pypi
@cindex pypi
Import metadata from the @uref{https://pypi.python.org/, Python Package
Index}@footnote{This functionality requires Guile-JSON to be installed.
@xref{Voraussetzungen}.}.  Information is taken from the JSON-formatted
description available at @code{pypi.python.org} and usually includes all the
relevant information, including package dependencies.  For maximum
efficiency, it is recommended to install the @command{unzip} utility, so
that the importer can unzip Python wheels and gather data from them.

The command below imports metadata for the @code{itsdangerous} Python
package:

@example
guix import pypi itsdangerous
@end example

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

@item gem
@cindex gem
Import metadata from @uref{https://rubygems.org/, RubyGems}@footnote{This
functionality requires Guile-JSON to be installed.  @xref{Voraussetzungen}.}.
Information is taken from the JSON-formatted description available at
@code{rubygems.org} and includes most relevant information, including
runtime dependencies.  There are some caveats, however.  The metadata
doesn't distinguish between synopses and descriptions, so the same string is
used for both fields.  Additionally, the details of non-Ruby dependencies
required to build native extensions is unavailable and left as an exercise
to the packager.

The command below imports metadata for the @code{rails} Ruby package:

@example
guix import gem rails
@end example

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

@item cpan
@cindex CPAN
Import metadata from @uref{https://www.metacpan.org/,
MetaCPAN}@footnote{This functionality requires Guile-JSON to be installed.
@xref{Voraussetzungen}.}.  Information is taken from the JSON-formatted
metadata provided through @uref{https://fastapi.metacpan.org/, MetaCPAN's
API} and includes most relevant information, such as module dependencies.
License information should be checked closely.  If Perl is available in the
store, then the @code{corelist} utility will be used to filter core modules
out of the list of dependencies.

The command command below imports metadata for the @code{Acme::Boolean} Perl
module:

@example
guix import cpan Acme::Boolean
@end example

@item cran
@cindex CRAN
@cindex Bioconductor
Import metadata from @uref{https://cran.r-project.org/, CRAN}, the central
repository for the @uref{http://r-project.org, GNU@tie{}R statistical and
graphical environment}.

Information is extracted from the @code{DESCRIPTION} file of the package.

The command command below imports metadata for the @code{Cairo} R package:

@example
guix import cran Cairo
@end example

When @code{--recursive} is added, the importer will traverse the dependency
graph of the given upstream package recursively and generate package
expressions for all those packages that are not yet in Guix.

When @code{--archive=bioconductor} is added, metadata is imported from
@uref{https://www.bioconductor.org/, Bioconductor}, a repository of R
packages for for the analysis and comprehension of high-throughput genomic
data in bioinformatics.

Information is extracted from the @code{DESCRIPTION} file of a package
published on the web interface of the Bioconductor SVN repository.

The command below imports metadata for the @code{GenomicRanges} R package:

@example
guix import cran --archive=bioconductor GenomicRanges
@end example

@item texlive
@cindex TeX Live
@cindex CTAN
Import metadata from @uref{http://www.ctan.org/, CTAN}, the comprehensive
TeX archive network for TeX packages that are part of the
@uref{https://www.tug.org/texlive/, TeX Live distribution}.

Information about the package is obtained through the XML API provided by
CTAN, while the source code is downloaded from the SVN repository of the Tex
Live project.  This is done because the CTAN does not keep versioned
archives.

The command command below imports metadata for the @code{fontspec} TeX
package:

@example
guix import texlive fontspec
@end example

When @code{--archive=DIRECTORY} is added, the source code is downloaded not
from the @file{latex} sub-directory of the @file{texmf-dist/source} tree in
the TeX Live SVN repository, but from the specified sibling directory under
the same root.

The command below imports metadata for the @code{ifxetex} package from CTAN
while fetching the sources from the directory @file{texmf/source/generic}:

@example
guix import texlive --archive=generic ifxetex
@end example

@item json
@cindex JSON, import
Import package metadata from a local JSON file@footnote{This functionality
requires Guile-JSON to be installed.  @xref{Voraussetzungen}.}.  Consider the
following example package definition in JSON format:

@example
@{
  "name": "hello",
  "version": "2.10",
  "source": "mirror://gnu/hello/hello-2.10.tar.gz",
  "build-system": "gnu",
  "home-page": "https://www.gnu.org/software/hello/",
  "synopsis": "Hello, GNU world: An example GNU package",
  "description": "GNU Hello prints a greeting.",
  "license": "GPL-3.0+",
  "native-inputs": ["gcc@@6"]
@}
@end example

The field names are the same as for the @code{<package>} record
(@xref{Pakete definieren}).  References to other packages are provided as
JSON lists of quoted package specification strings such as @code{guile} or
@code{guile@@2.0}.

The importer also supports a more explicit source definition using the
common fields for @code{<origin>} records:

@example
@{
  @dots{}
  "source": @{
    "method": "url-fetch",
    "uri": "mirror://gnu/hello/hello-2.10.tar.gz",
    "sha256": @{
      "base32": "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"
    @}
  @}
  @dots{}
@}
@end example

The command below reads metadata from the JSON file @code{hello.json} and
outputs a package expression:

@example
guix import json hello.json
@end example

@item nix
Import metadata from a local copy of the source of the
@uref{http://nixos.org/nixpkgs/, Nixpkgs distribution}@footnote{This relies
on the @command{nix-instantiate} command of @uref{http://nixos.org/nix/,
Nix}.}.  Package definitions in Nixpkgs are typically written in a mixture
of Nix-language and Bash code.  This command only imports the high-level
package structure that is written in the Nix language.  It normally includes
all the basic fields of a package definition.

When importing a GNU package, the synopsis and descriptions are replaced by
their canonical upstream variant.

Usually, you will first need to do:

@example
export NIX_REMOTE=daemon
@end example

@noindent
so that @command{nix-instantiate} does not try to open the Nix database.

As an example, the command below imports the package definition of
LibreOffice (more precisely, it imports the definition of the package bound
to the @code{libreoffice} top-level attribute):

@example
guix import nix ~/path/to/nixpkgs libreoffice
@end example

@item hackage
@cindex hackage
Import metadata from the Haskell community's central package archive
@uref{https://hackage.haskell.org/, Hackage}.  Information is taken from
Cabal files and includes all the relevant information, including package
dependencies.

Specific command-line options are:

@table @code
@item --stdin
@itemx -s
Read a Cabal file from standard input.
@item --no-test-dependencies
@itemx -t
Do not include dependencies required only by the test suites.
@item --cabal-environment=@var{alist}
@itemx -e @var{alist}
@var{alist} is a Scheme alist defining the environment in which the Cabal
conditionals are evaluated.  The accepted keys are: @code{os}, @code{arch},
@code{impl} and a string representing the name of a flag.  The value
associated with a flag has to be either the symbol @code{true} or
@code{false}.  The value associated with other keys has to conform to the
Cabal file format definition.  The default value associated with the keys
@code{os}, @code{arch} and @code{impl} is @samp{linux}, @samp{x86_64} and
@samp{ghc}, respectively.
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

The command below imports metadata for the latest version of the @code{HTTP}
Haskell package without including test dependencies and specifying the value
of the flag @samp{network-uri} as @code{false}:

@example
guix import hackage -t -e "'((\"network-uri\" . false))" HTTP
@end example

A specific package version may optionally be specified by following the
package name by an at-sign and a version number as in the following example:

@example
guix import hackage mtl@@2.1.3.1
@end example

@item stackage
@cindex stackage
The @code{stackage} importer is a wrapper around the @code{hackage} one.  It
takes a package name, looks up the package version included in a long-term
support (LTS) @uref{https://www.stackage.org, Stackage} release and uses the
@code{hackage} importer to retrieve its metadata.  Note that it is up to you
to select an LTS release compatible with the GHC compiler used by Guix.

Specific command-line options are:

@table @code
@item --no-test-dependencies
@itemx -t
Do not include dependencies required only by the test suites.
@item --lts-version=@var{version}
@itemx -l @var{version}
@var{version} is the desired LTS release version.  If omitted the latest
release is used.
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

The command below imports metadata for the @code{HTTP} Haskell package
included in the LTS Stackage release version 7.18:

@example
guix import stackage --lts-version=7.18 HTTP
@end example

@item elpa
@cindex elpa
Import metadata from an Emacs Lisp Package Archive (ELPA) package repository
(@pxref{Packages,,, emacs, The GNU Emacs Manual}).

Specific command-line options are:

@table @code
@item --archive=@var{repo}
@itemx -a @var{repo}
@var{repo} identifies the archive repository from which to retrieve the
information.  Currently the supported repositories and their identifiers
are:
@itemize -
@item
@uref{http://elpa.gnu.org/packages, GNU}, selected by the @code{gnu}
identifier.  This is the default.

Packages from @code{elpa.gnu.org} are signed with one of the keys contained
in the GnuPG keyring at @file{share/emacs/25.1/etc/package-keyring.gpg} (or
similar) in the @code{emacs} package (@pxref{Package Installation, ELPA
package signatures,, emacs, The GNU Emacs Manual}).

@item
@uref{http://stable.melpa.org/packages, MELPA-Stable}, selected by the
@code{melpa-stable} identifier.

@item
@uref{http://melpa.org/packages, MELPA}, selected by the @code{melpa}
identifier.
@end itemize

@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

@item crate
@cindex crate
Import metadata from the crates.io Rust package repository
@uref{https://crates.io, crates.io}.

@item opam
@cindex OPAM
@cindex OCaml
Import metadata from the @uref{https://opam.ocaml.org/, OPAM} package
repository used by the OCaml community.
@end table

The structure of the @command{guix import} code is modular.  It would be
useful to have more importers for other package formats, and your help is
welcome here (@pxref{Mitwirken}).

@node Aufruf von guix refresh
@section Invoking @command{guix refresh}

@cindex @command{guix refresh}
The primary audience of the @command{guix refresh} command is developers of
the GNU software distribution.  By default, it reports any packages provided
by the distribution that are outdated compared to the latest upstream
version, like this:

@example
$ guix refresh
gnu/packages/gettext.scm:29:13: gettext would be upgraded from 0.18.1.1 to 0.18.2.1
gnu/packages/glib.scm:77:12: glib would be upgraded from 2.34.3 to 2.37.0
@end example

Alternately, one can specify packages to consider, in which case a warning
is emitted for packages that lack an updater:

@example
$ guix refresh coreutils guile guile-ssh
gnu/packages/ssh.scm:205:2: warning: no updater for guile-ssh
gnu/packages/guile.scm:136:12: guile would be upgraded from 2.0.12 to 2.0.13
@end example

@command{guix refresh} browses the upstream repository of each package and
determines the highest version number of the releases therein.  The command
knows how to update specific types of packages: GNU packages, ELPA packages,
etc.---see the documentation for @option{--type} below.  There are many
packages, though, for which it lacks a method to determine whether a new
upstream release is available.  However, the mechanism is extensible, so
feel free to get in touch with us to add a new method!

Sometimes the upstream name differs from the package name used in Guix, and
@command{guix refresh} needs a little help.  Most updaters honor the
@code{upstream-name} property in package definitions, which can be used to
that effect:

@example
(define-public network-manager
  (package
    (name "network-manager")
    ;; @dots{}
    (properties '((upstream-name . "NetworkManager")))))
@end example

When passed @code{--update}, it modifies distribution source files to update
the version numbers and source tarball hashes of those package recipes
(@pxref{Pakete definieren}).  This is achieved by downloading each package's
latest source tarball and its associated OpenPGP signature, authenticating
the downloaded tarball against its signature using @command{gpg}, and
finally computing its hash.  When the public key used to sign the tarball is
missing from the user's keyring, an attempt is made to automatically
retrieve it from a public key server; when this is successful, the key is
added to the user's keyring; otherwise, @command{guix refresh} reports an
error.

The following options are supported:

@table @code

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This is useful to precisely refer to a package, as in this example:

@example
guix refresh -l -e '(@@@@ (gnu packages commencement) glibc-final)'
@end example

This command lists the dependents of the ``final'' libc (essentially all the
packages.)

@item --update
@itemx -u
Update distribution source files (package recipes) in place.  This is
usually run from a checkout of the Guix source tree (@pxref{Guix vor der Installation ausführen}):

@example
$ ./pre-inst-env guix refresh -s non-core -u
@end example

@xref{Pakete definieren}, for more information on package definitions.

@item --select=[@var{subset}]
@itemx -s @var{subset}
Select all the packages in @var{subset}, one of @code{core} or
@code{non-core}.

The @code{core} subset refers to all the packages at the core of the
distribution---i.e., packages that are used to build ``everything else''.
This includes GCC, libc, Binutils, Bash, etc.  Usually, changing one of
these packages in the distribution entails a rebuild of all the others.
Thus, such updates are an inconvenience to users in terms of build time or
bandwidth used to achieve the upgrade.

The @code{non-core} subset refers to the remaining packages.  It is
typically useful in cases where an update of the core packages would be
inconvenient.

@item --manifest=@var{Datei}
@itemx -m @var{Datei}
Select all the packages from the manifest in @var{file}. This is useful to
check if any packages of the user manifest can be updated.

@item --type=@var{updater}
@itemx -t @var{updater}
Select only packages handled by @var{updater} (may be a comma-separated list
of updaters).  Currently, @var{updater} may be one of:

@table @code
@item gnu
the updater for GNU packages;
@item gnome
the updater for GNOME packages;
@item kde
the updater for KDE packages;
@item xorg
the updater for X.org packages;
@item kernel.org
the updater for packages hosted on kernel.org;
@item elpa
the updater for @uref{http://elpa.gnu.org/, ELPA} packages;
@item cran
the updater for @uref{https://cran.r-project.org/, CRAN} packages;
@item bioconductor
the updater for @uref{https://www.bioconductor.org/, Bioconductor} R
packages;
@item cpan
the updater for @uref{http://www.cpan.org/, CPAN} packages;
@item pypi
the updater for @uref{https://pypi.python.org, PyPI} packages.
@item gem
the updater for @uref{https://rubygems.org, RubyGems} packages.
@item github
the updater for @uref{https://github.com, GitHub} packages.
@item hackage
the updater for @uref{https://hackage.haskell.org, Hackage} packages.
@item stackage
the updater for @uref{https://www.stackage.org, Stackage} packages.
@item crate
the updater for @uref{https://crates.io, Crates} packages.
@end table

For instance, the following command only checks for updates of Emacs
packages hosted at @code{elpa.gnu.org} and for updates of CRAN packages:

@example
$ guix refresh --type=elpa,cran
gnu/packages/statistics.scm:819:13: r-testthat would be upgraded from 0.10.0 to 0.11.0
gnu/packages/emacs.scm:856:13: emacs-auctex would be upgraded from 11.88.6 to 11.88.9
@end example

@end table

In addition, @command{guix refresh} can be passed one or more package names,
as in this example:

@example
$ ./pre-inst-env guix refresh -u emacs idutils gcc@@4.8
@end example

@noindent
The command above specifically updates the @code{emacs} and @code{idutils}
packages.  The @code{--select} option would have no effect in this case.

When considering whether to upgrade a package, it is sometimes convenient to
know which packages would be affected by the upgrade and should be checked
for compatibility.  For this the following option may be used when passing
@command{guix refresh} one or more package names:

@table @code

@item --list-updaters
@itemx -L
List available updaters and exit (see @option{--type} above.)

For each updater, display the fraction of packages it covers; at the end,
display the fraction of packages covered by all these updaters.

@item --list-dependent
@itemx -l
List top-level dependent packages that would need to be rebuilt as a result
of upgrading one or more packages.

@xref{Aufruf von guix graph, the @code{reverse-package} type of @command{guix
graph}}, for information on how to visualize the list of dependents of a
package.

@end table

Be aware that the @code{--list-dependent} option only @emph{approximates}
the rebuilds that would be required as a result of an upgrade.  More
rebuilds might be required under some circumstances.

@example
$ guix refresh --list-dependent flex
Building the following 120 packages would ensure 213 dependent packages are rebuilt:
hop@@2.4.0 geiser@@0.4 notmuch@@0.18 mu@@0.9.9.5 cflow@@1.4 idutils@@4.6 @dots{}
@end example

The command above lists a set of packages that could be built to check for
compatibility with an upgraded @code{flex} package.

The following options can be used to customize GnuPG operation:

@table @code

@item --gpg=@var{command}
Use @var{command} as the GnuPG 2.x command.  @var{command} is searched for
in @code{$PATH}.

@item --keyring=@var{file}
Use @var{file} as the keyring for upstream keys.  @var{file} must be in the
@dfn{keybox format}.  Keybox files usually have a name ending in @file{.kbx}
and the GNU@tie{}Privacy Guard (GPG) can manipulate these files
(@pxref{kbxutil, @command{kbxutil},, gnupg, Using the GNU Privacy Guard},
for information on a tool to manipulate keybox files).

When this option is omitted, @command{guix refresh} uses
@file{~/.config/guix/upstream/trustedkeys.kbx} as the keyring for upstream
signing keys.  OpenPGP signatures are checked against keys from this
keyring; missing keys are downloaded to this keyring as well (see
@option{--key-download} below.)

You can export keys from your default GPG keyring into a keybox file using
commands like this one:

@example
gpg --export rms@@gnu.org | kbxutil --import-openpgp >> mykeyring.kbx
@end example

Likewise, you can fetch keys to a specific keybox file like this:

@example
gpg --no-default-keyring --keyring mykeyring.kbx \
  --recv-keys @value{OPENPGP-SIGNING-KEY-ID}
@end example

@ref{GPG Configuration Options, @option{--keyring},, gnupg, Using the GNU
Privacy Guard}, for more information on GPG's @option{--keyring} option.

@item --key-download=@var{policy}
Handle missing OpenPGP keys according to @var{policy}, which may be one of:

@table @code
@item always
Always download missing OpenPGP keys from the key server, and add them to
the user's GnuPG keyring.

@item never
Never try to download missing OpenPGP keys.  Instead just bail out.

@item interactive
When a package signed with an unknown OpenPGP key is encountered, ask the
user whether to download it or not.  This is the default behavior.
@end table

@item --key-server=@var{host}
Use @var{host} as the OpenPGP key server when importing a public key.

@end table

The @code{github} updater uses the @uref{https://developer.github.com/v3/,
GitHub API} to query for new releases.  When used repeatedly e.g. when
refreshing all packages, GitHub will eventually refuse to answer any further
API requests.  By default 60 API requests per hour are allowed, and a full
refresh on all GitHub packages in Guix requires more than this.
Authentication with GitHub through the use of an API token alleviates these
limits.  To use an API token, set the environment variable
@code{GUIX_GITHUB_TOKEN} to a token procured from
@uref{https://github.com/settings/tokens} or otherwise.


@node Aufruf von guix lint
@section Invoking @command{guix lint}

@cindex @command{guix lint}
@cindex package, checking for errors
The @command{guix lint} command is meant to help package developers avoid
common errors and use a consistent style.  It runs a number of checks on a
given set of packages in order to find common mistakes in their
definitions.  Available @dfn{checkers} include (see @code{--list-checkers}
for a complete list):

@table @code
@item synopsis
@itemx description
Validate certain typographical and stylistic rules about package
descriptions and synopses.

@item inputs-should-be-native
Identify inputs that should most likely be native inputs.

@item source
@itemx home-page
@itemx mirror-url
@itemx source-file-name
Probe @code{home-page} and @code{source} URLs and report those that are
invalid.  Suggest a @code{mirror://} URL when applicable.  Check that the
source file name is meaningful, e.g. is not just a version number or
``git-checkout'', without a declared @code{file-name} (@pxref{„origin“-Referenz}).

@item cve
@cindex security vulnerabilities
@cindex CVE, Common Vulnerabilities and Exposures
Report known vulnerabilities found in the Common Vulnerabilities and
Exposures (CVE) databases of the current and past year
@uref{https://nvd.nist.gov/download.cfm#CVE_FEED, published by the US NIST}.

To view information about a particular vulnerability, visit pages such as:

@itemize
@item
@indicateurl{https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-YYYY-ABCD}
@item
@indicateurl{https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-YYYY-ABCD}
@end itemize

@noindent
where @code{CVE-YYYY-ABCD} is the CVE identifier---e.g.,
@code{CVE-2015-7554}.

Package developers can specify in package recipes the
@uref{https://nvd.nist.gov/cpe.cfm,Common Platform Enumeration (CPE)} name
and version of the package when they differ from the name or version that
Guix uses, as in this example:

@example
(package
  (name "grub")
  ;; @dots{}
  ;; CPE calls this package "grub2".
  (properties '((cpe-name . "grub2")
                (cpe-version . "2.3")))
@end example

@c See <http://www.openwall.com/lists/oss-security/2017/03/15/3>.
Some entries in the CVE database do not specify which version of a package
they apply to, and would thus ``stick around'' forever.  Package developers
who found CVE alerts and verified they can be ignored can declare them as in
this example:

@example
(package
  (name "t1lib")
  ;; @dots{}
  ;; These CVEs no longer apply and can be safely ignored.
  (properties `((lint-hidden-cve . ("CVE-2011-0433"
                                    "CVE-2011-1553"
                                    "CVE-2011-1554"
                                    "CVE-2011-5244")))))
@end example

@item formatting
Warn about obvious source code formatting issues: trailing white space, use
of tabulations, etc.
@end table

The general syntax is:

@example
guix lint @var{options} @var{package}@dots{}
@end example

If no package is given on the command line, then all packages are checked.
The @var{options} may be zero or more of the following:

@table @code
@item --list-checkers
@itemx -l
List and describe all the available checkers that will be run on packages
and exit.

@item --checkers
@itemx -c
Only enable the checkers specified in a comma-separated list using the names
returned by @code{--list-checkers}.

@end table

@node Aufruf von guix size
@section Invoking @command{guix size}

@cindex size
@cindex package size
@cindex Abschluss
@cindex @command{guix size}
The @command{guix size} command helps package developers profile the disk
usage of packages.  It is easy to overlook the impact of an additional
dependency added to a package, or the impact of using a single output for a
package that could easily be split (@pxref{Pakete mit mehreren Ausgaben.}).  Such are the typical issues that @command{guix size} can
highlight.

The command can be passed one or more package specifications such as
@code{gcc@@4.8} or @code{guile:debug}, or a file name in the store.
Consider this example:

@example
$ guix size coreutils
store item                               total    self
/gnu/store/@dots{}-gcc-5.5.0-lib           60.4    30.1  38.1%
/gnu/store/@dots{}-glibc-2.27              30.3    28.8  36.6%
/gnu/store/@dots{}-coreutils-8.28          78.9    15.0  19.0%
/gnu/store/@dots{}-gmp-6.1.2               63.1     2.7   3.4%
/gnu/store/@dots{}-bash-static-4.4.12       1.5     1.5   1.9%
/gnu/store/@dots{}-acl-2.2.52              61.1     0.4   0.5%
/gnu/store/@dots{}-attr-2.4.47             60.6     0.2   0.3%
/gnu/store/@dots{}-libcap-2.25             60.5     0.2   0.2%
total: 78.9 MiB
@end example

@cindex Abschluss
The store items listed here constitute the @dfn{transitive closure} of
Coreutils---i.e., Coreutils and all its dependencies, recursively---as would
be returned by:

@example
$ guix gc -R /gnu/store/@dots{}-coreutils-8.23
@end example

Here the output shows three columns next to store items.  The first column,
labeled ``total'', shows the size in mebibytes (MiB) of the closure of the
store item---that is, its own size plus the size of all its dependencies.
The next column, labeled ``self'', shows the size of the item itself.  The
last column shows the ratio of the size of the item itself to the space
occupied by all the items listed here.

In this example, we see that the closure of Coreutils weighs in at
79@tie{}MiB, most of which is taken by libc and GCC's run-time support
libraries.  (That libc and GCC's libraries represent a large fraction of the
closure is not a problem @i{per se} because they are always available on the
system anyway.)

When the package(s) passed to @command{guix size} are available in the
store@footnote{More precisely, @command{guix size} looks for the
@emph{ungrafted} variant of the given package(s), as returned by @code{guix
build @var{package} --no-grafts}.  @xref{Sicherheitsaktualisierungen}, for information
on grafts.}, @command{guix size} queries the daemon to determine its
dependencies, and measures its size in the store, similar to @command{du -ms
--apparent-size} (@pxref{du invocation,,, coreutils, GNU Coreutils}).

When the given packages are @emph{not} in the store, @command{guix size}
reports information based on the available substitutes
(@pxref{Substitute}).  This makes it possible it to profile disk usage of
store items that are not even on disk, only available remotely.

You can also specify several package names:

@example
$ guix size coreutils grep sed bash
store item                               total    self
/gnu/store/@dots{}-coreutils-8.24          77.8    13.8  13.4%
/gnu/store/@dots{}-grep-2.22               73.1     0.8   0.8%
/gnu/store/@dots{}-bash-4.3.42             72.3     4.7   4.6%
/gnu/store/@dots{}-readline-6.3            67.6     1.2   1.2%
@dots{}
total: 102.3 MiB
@end example

@noindent
In this example we see that the combination of the four packages takes
102.3@tie{}MiB in total, which is much less than the sum of each closure
since they have a lot of dependencies in common.

The available options are:

@table @option

@item --substitute-urls=@var{URLs}
Use substitute information from @var{urls}.  @xref{client-substitute-urls,
the same option for @code{guix build}}.

@item --sort=@var{key}
Sort lines according to @var{key}, one of the following options:

@table @code
@item self
the size of each item (the default);
@item Abschluss
the total size of the item's closure.
@end table

@item --map-file=@var{file}
Write a graphical map of disk usage in PNG format to @var{file}.

For the example above, the map looks like this:

@image{images/coreutils-size-map,5in,, map of Coreutils disk usage produced
by @command{guix size}}

This option requires that
@uref{http://wingolog.org/software/guile-charting/, Guile-Charting} be
installed and visible in Guile's module search path.  When that is not the
case, @command{guix size} fails as it tries to load it.

@item --system=@var{System}
@itemx -s @var{system}
Consider packages for @var{system}---e.g., @code{x86_64-linux}.

@end table

@node Aufruf von guix graph
@section Invoking @command{guix graph}

@cindex DAG
@cindex @command{guix graph}
@cindex Paketabhängigkeiten
Packages and their dependencies form a @dfn{graph}, specifically a directed
acyclic graph (DAG).  It can quickly become difficult to have a mental model
of the package DAG, so the @command{guix graph} command provides a visual
representation of the DAG.  By default, @command{guix graph} emits a DAG
representation in the input format of @uref{http://www.graphviz.org/,
Graphviz}, so its output can be passed directly to the @command{dot} command
of Graphviz.  It can also emit an HTML page with embedded JavaScript code to
display a ``chord diagram'' in a Web browser, using the
@uref{https://d3js.org/, d3.js} library, or emit Cypher queries to construct
a graph in a graph database supporting the @uref{http://www.opencypher.org/,
openCypher} query language.  The general syntax is:

@example
guix graph @var{options} @var{package}@dots{}
@end example

For example, the following command generates a PDF file representing the
package DAG for the GNU@tie{}Core Utilities, showing its build-time
dependencies:

@example
guix graph coreutils | dot -Tpdf > dag.pdf
@end example

The output looks like this:

@image{images/coreutils-graph,2in,,Dependency graph of the GNU Coreutils}

Nice little graph, no?

But there is more than one graph! The one above is concise: it is the graph
of package objects, omitting implicit inputs such as GCC, libc, grep, etc.
It is often useful to have such a concise graph, but sometimes one may want
to see more details.  @command{guix graph} supports several types of graphs,
allowing you to choose the level of detail:

@table @code
@item package
This is the default type used in the example above.  It shows the DAG of
package objects, excluding implicit dependencies.  It is concise, but
filters out many details.

@item reverse-package
This shows the @emph{reverse} DAG of packages.  For example:

@example
guix graph --type=reverse-package ocaml
@end example

... yields the graph of packages that depend on OCaml.

Note that for core packages this can yield huge graphs.  If all you want is
to know the number of packages that depend on a given package, use
@command{guix refresh --list-dependent} (@pxref{Aufruf von guix refresh,
@option{--list-dependent}}).

@item bag-emerged
This is the package DAG, @emph{including} implicit inputs.

For instance, the following command:

@example
guix graph --type=bag-emerged coreutils | dot -Tpdf > dag.pdf
@end example

... yields this bigger graph:

@image{images/coreutils-bag-graph,,5in,Detailed dependency graph of the GNU
Coreutils}

At the bottom of the graph, we see all the implicit inputs of
@var{gnu-build-system} (@pxref{Erstellungssysteme, @code{gnu-build-system}}).

Now, note that the dependencies of these implicit inputs---that is, the
@dfn{bootstrap dependencies} (@pxref{Bootstrapping})---are not shown here,
for conciseness.

@item bag
Similar to @code{bag-emerged}, but this time including all the bootstrap
dependencies.

@item bag-with-origins
Similar to @code{bag}, but also showing origins and their dependencies.

@item Ableitung
This is the most detailed representation: It shows the DAG of derivations
(@pxref{Ableitungen}) and plain store items.  Compared to the above
representation, many additional nodes are visible, including build scripts,
patches, Guile modules, etc.

For this type of graph, it is also possible to pass a @file{.drv} file name
instead of a package name, as in:

@example
guix graph -t derivation `guix system build -d my-config.scm`
@end example

@item module
This is the graph of @dfn{package modules} (@pxref{Paketmodule}).  For
example, the following command shows the graph for the package module that
defines the @code{guile} package:

@example
guix graph -t module guile | dot -Tpdf > module-graph.pdf
@end example
@end table

All the types above correspond to @emph{build-time dependencies}.  The
following graph type represents the @emph{run-time dependencies}:

@table @code
@item references
This is the graph of @dfn{references} of a package output, as returned by
@command{guix gc --references} (@pxref{Aufruf von guix gc}).

If the given package output is not available in the store, @command{guix
graph} attempts to obtain dependency information from substitutes.

Here you can also pass a store file name instead of a package name.  For
example, the command below produces the reference graph of your profile
(which can be big!):

@example
guix graph -t references `readlink -f ~/.guix-profile`
@end example

@item referrers
This is the graph of the @dfn{referrers} of a store item, as returned by
@command{guix gc --referrers} (@pxref{Aufruf von guix gc}).

This relies exclusively on local information from your store.  For instance,
let us suppose that the current Inkscape is available in 10 profiles on your
machine; @command{guix graph -t referrers inkscape} will show a graph rooted
at Inkscape and with those 10 profiles linked to it.

It can help determine what is preventing a store item from being garbage
collected.

@end table

The available options are the following:

@table @option
@item --type=@var{type}
@itemx -t @var{type}
Produce a graph output of @var{type}, where @var{type} must be one of the
values listed above.

@item --list-types
List the supported graph types.

@item --backend=@var{backend}
@itemx -b @var{backend}
Produce a graph using the selected @var{backend}.

@item --list-backends
List the supported graph backends.

Currently, the available backends are Graphviz and d3.js.

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This is useful to precisely refer to a package, as in this example:

@example
guix graph -e '(@@@@ (gnu packages commencement) gnu-make-final)'
@end example

@item --system=@var{System}
@itemx -s @var{system}
Display the graph for @var{system}---e.g., @code{i686-linux}.

The package dependency graph is largely architecture-independent, but there
are some architecture-dependent bits that this option allows you to
visualize.
@end table


@node Aufruf von guix environment
@section Invoking @command{guix environment}

@cindex reproducible build environments
@cindex development environments
@cindex @command{guix environment}
@cindex environment, package build environment
The purpose of @command{guix environment} is to assist hackers in creating
reproducible development environments without polluting their package
profile.  The @command{guix environment} tool takes one or more packages,
builds all of their inputs, and creates a shell environment to use them.

The general syntax is:

@example
guix environment @var{options} @var{package}@dots{}
@end example

The following example spawns a new shell set up for the development of
GNU@tie{}Guile:

@example
guix environment guile
@end example

If the needed dependencies are not built yet, @command{guix environment}
automatically builds them.  The environment of the new shell is an augmented
version of the environment that @command{guix environment} was run in.  It
contains the necessary search paths for building the given package added to
the existing environment variables.  To create a ``pure'' environment, in
which the original environment variables have been unset, use the
@code{--pure} option@footnote{Users sometimes wrongfully augment environment
variables such as @code{PATH} in their @file{~/.bashrc} file.  As a
consequence, when @code{guix environment} launches it, Bash may read
@file{~/.bashrc}, thereby introducing ``impurities'' in these environment
variables.  It is an error to define such environment variables in
@file{.bashrc}; instead, they should be defined in @file{.bash_profile},
which is sourced only by log-in shells.  @xref{Bash Startup Files,,, bash,
The GNU Bash Reference Manual}, for details on Bash start-up files.}.

@vindex GUIX_ENVIRONMENT
@command{guix environment} defines the @code{GUIX_ENVIRONMENT} variable in
the shell it spawns; its value is the file name of the profile of this
environment.  This allows users to, say, define a specific prompt for
development environments in their @file{.bashrc} (@pxref{Bash Startup
Files,,, bash, The GNU Bash Reference Manual}):

@example
if [ -n "$GUIX_ENVIRONMENT" ]
then
    export PS1="\u@@\h \w [dev]\$ "
fi
@end example

@noindent
... or to browse the profile:

@example
$ ls "$GUIX_ENVIRONMENT/bin"
@end example

Additionally, more than one package may be specified, in which case the
union of the inputs for the given packages are used.  For example, the
command below spawns a shell where all of the dependencies of both Guile and
Emacs are available:

@example
guix environment guile emacs
@end example

Sometimes an interactive shell session is not desired.  An arbitrary command
may be invoked by placing the @code{--} token to separate the command from
the rest of the arguments:

@example
guix environment guile -- make -j4
@end example

In other situations, it is more convenient to specify the list of packages
needed in the environment.  For example, the following command runs
@command{python} from an environment containing Python@tie{}2.7 and NumPy:

@example
guix environment --ad-hoc python2-numpy python-2.7 -- python
@end example

Furthermore, one might want the dependencies of a package and also some
additional packages that are not build-time or runtime dependencies, but are
useful when developing nonetheless.  Because of this, the @code{--ad-hoc}
flag is positional.  Packages appearing before @code{--ad-hoc} are
interpreted as packages whose dependencies will be added to the
environment.  Packages appearing after are interpreted as packages that will
be added to the environment directly.  For example, the following command
creates a Guix development environment that additionally includes Git and
strace:

@example
guix environment guix --ad-hoc git strace
@end example

Sometimes it is desirable to isolate the environment as much as possible,
for maximal purity and reproducibility.  In particular, when using Guix on a
host distro that is not GuixSD, it is desirable to prevent access to
@file{/usr/bin} and other system-wide resources from the development
environment.  For example, the following command spawns a Guile REPL in a
``container'' where only the store and the current working directory are
mounted:

@example
guix environment --ad-hoc --container guile -- guile
@end example

@quotation Anmerkung
The @code{--container} option requires Linux-libre 3.19 or newer.
@end quotation

The available options are summarized below.

@table @code
@item --root=@var{file}
@itemx -r @var{file}
@cindex persistent environment
@cindex garbage collector root, for environments
Make @var{file} a symlink to the profile for this environment, and register
it as a garbage collector root.

This is useful if you want to protect your environment from garbage
collection, to make it ``persistent''.

When this option is omitted, the environment is protected from garbage
collection only for the duration of the @command{guix environment} session.
This means that next time you recreate the same environment, you could have
to rebuild or re-download packages.  @xref{Aufruf von guix gc}, for more on GC
roots.

@item --expression=@var{expr}
@itemx -e @var{expr}
Create an environment for the package or list of packages that @var{expr}
evaluates to.

For example, running:

@example
guix environment -e '(@@ (gnu packages maths) petsc-openmpi)'
@end example

starts a shell with the environment for this specific variant of the PETSc
package.

Running:

@example
guix environment --ad-hoc -e '(@@ (gnu) %base-packages)'
@end example

starts a shell with all the GuixSD base packages available.

The above commands only use the default output of the given packages.  To
select other outputs, two element tuples can be specified:

@example
guix environment --ad-hoc -e '(list (@@ (gnu packages bash) bash) "include")'
@end example

@item --load=@var{file}
@itemx -l @var{file}
Create an environment for the package or list of packages that the code
within @var{file} evaluates to.

Zum Beispiel könnte die @var{Datei} eine Definition wie diese enthalten
(@pxref{Pakete definieren}):

@example
@verbatiminclude environment-gdb.scm
@end example

@item --manifest=@var{Datei}
@itemx -m @var{Datei}
Create an environment for the packages contained in the manifest object
returned by the Scheme code in @var{file}.

This is similar to the same-named option in @command{guix package}
(@pxref{profile-manifest, @option{--manifest}}) and uses the same manifest
files.

@item --ad-hoc
Include all specified packages in the resulting environment, as if an @i{ad
hoc} package were defined with them as inputs.  This option is useful for
quickly creating an environment without having to write a package expression
to contain the desired inputs.

For instance, the command:

@example
guix environment --ad-hoc guile guile-sdl -- guile
@end example

runs @command{guile} in an environment where Guile and Guile-SDL are
available.

Note that this example implicitly asks for the default output of
@code{guile} and @code{guile-sdl}, but it is possible to ask for a specific
output---e.g., @code{glib:bin} asks for the @code{bin} output of @code{glib}
(@pxref{Pakete mit mehreren Ausgaben.}).

This option may be composed with the default behavior of @command{guix
environment}.  Packages appearing before @code{--ad-hoc} are interpreted as
packages whose dependencies will be added to the environment, the default
behavior.  Packages appearing after are interpreted as packages that will be
added to the environment directly.

@item --pure
Unset existing environment variables when building the new environment.
This has the effect of creating an environment in which search paths only
contain package inputs.

@item --search-paths
Display the environment variable definitions that make up the environment.

@item --system=@var{System}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}.

@item --container
@itemx -C
@cindex container
Run @var{command} within an isolated container.  The current working
directory outside the container is mapped inside the container.
Additionally, unless overridden with @code{--user}, a dummy home directory
is created that matches the current user's home directory, and
@file{/etc/passwd} is configured accordingly.  The spawned process runs as
the current user outside the container, but has root privileges in the
context of the container.

@item --network
@itemx -N
For containers, share the network namespace with the host system.
Containers created without this flag only have access to the loopback
device.

@item --link-profile
@itemx -P
For containers, link the environment profile to @file{~/.guix-profile}
within the container.  This is equivalent to running the command @command{ln
-s $GUIX_ENVIRONMENT ~/.guix-profile} within the container.  Linking will
fail and abort the environment if the directory already exists, which will
certainly be the case if @command{guix environment} was invoked in the
user's home directory.

Certain packages are configured to look in @code{~/.guix-profile} for
configuration files and data;@footnote{For example, the @code{fontconfig}
package inspects @file{~/.guix-profile/share/fonts} for additional fonts.}
@code{--link-profile} allows these programs to behave as expected within the
environment.

@item --user=@var{user}
@itemx -u @var{user}
For containers, use the username @var{user} in place of the current user.
The generated @file{/etc/passwd} entry within the container will contain the
name @var{user}; the home directory will be @file{/home/USER}; and no user
GECOS data will be copied.  @var{user} need not exist on the system.

Additionally, any shared or exposed path (see @code{--share} and
@code{--expose} respectively) whose target is within the current user's home
directory will be remapped relative to @file{/home/USER}; this includes the
automatic mapping of the current working directory.

@example
# will expose paths as /home/foo/wd, /home/foo/test, and /home/foo/target
cd $HOME/wd
guix environment --container --user=foo \
     --expose=$HOME/test \
     --expose=/tmp/target=$HOME/target
@end example

While this will limit the leaking of user identity through home paths and
each of the user fields, this is only one useful component of a broader
privacy/anonymity solution---not one in and of itself.

@item --expose=@var{source}[=@var{target}]
For containers, expose the file system @var{source} from the host system as
the read-only file system @var{target} within the container.  If
@var{target} is not specified, @var{source} is used as the target mount
point in the container.

The example below spawns a Guile REPL in a container in which the user's
home directory is accessible read-only via the @file{/exchange} directory:

@example
guix environment --container --expose=$HOME=/exchange --ad-hoc guile -- guile
@end example

@item --share=@var{source}[=@var{target}]
For containers, share the file system @var{source} from the host system as
the writable file system @var{target} within the container.  If @var{target}
is not specified, @var{source} is used as the target mount point in the
container.

The example below spawns a Guile REPL in a container in which the user's
home directory is accessible for both reading and writing via the
@file{/exchange} directory:

@example
guix environment --container --share=$HOME=/exchange --ad-hoc guile -- guile
@end example
@end table

@command{guix environment} also supports all of the common build options
that @command{guix build} supports (@pxref{Gemeinsame Erstellungsoptionen}).


@node Aufruf von guix publish
@section Invoking @command{guix publish}

@cindex @command{guix publish}
The purpose of @command{guix publish} is to enable users to easily share
their store with others, who can then use it as a substitute server
(@pxref{Substitute}).

When @command{guix publish} runs, it spawns an HTTP server which allows
anyone with network access to obtain substitutes from it.  This means that
any machine running Guix can also act as if it were a build farm, since the
HTTP interface is compatible with Hydra, the software behind the
@code{hydra.gnu.org} build farm.

For security, each substitute is signed, allowing recipients to check their
authenticity and integrity (@pxref{Substitute}).  Because @command{guix
publish} uses the signing key of the system, which is only readable by the
system administrator, it must be started as root; the @code{--user} option
makes it drop root privileges early on.

The signing key pair must be generated before @command{guix publish} is
launched, using @command{guix archive --generate-key} (@pxref{Aufruf von guix archive}).

The general syntax is:

@example
guix publish @var{options}@dots{}
@end example

Running @command{guix publish} without any additional arguments will spawn
an HTTP server on port 8080:

@example
guix publish
@end example

Once a publishing server has been authorized (@pxref{Aufruf von guix archive}), the daemon may download substitutes from it:

@example
guix-daemon --substitute-urls=http://example.org:8080
@end example

By default, @command{guix publish} compresses archives on the fly as it
serves them.  This ``on-the-fly'' mode is convenient in that it requires no
setup and is immediately available.  However, when serving lots of clients,
we recommend using the @option{--cache} option, which enables caching of the
archives before they are sent to clients---see below for details.  The
@command{guix weather} command provides a handy way to check what a server
provides (@pxref{Aufruf von guix weather}).

As a bonus, @command{guix publish} also serves as a content-addressed mirror
for source files referenced in @code{origin} records (@pxref{„origin“-Referenz}).  For instance, assuming @command{guix publish} is running on
@code{example.org}, the following URL returns the raw
@file{hello-2.10.tar.gz} file with the given SHA256 hash (represented in
@code{nix-base32} format, @pxref{Aufruf von guix hash}):

@example
http://example.org/file/hello-2.10.tar.gz/sha256/0ssi1@dots{}ndq1i
@end example

Obviously, these URLs only work for files that are in the store; in other
cases, they return 404 (``Not Found'').

@cindex build logs, publication
Build logs are available from @code{/log} URLs like:

@example
http://example.org/log/gwspk@dots{}-guile-2.2.3
@end example

@noindent
When @command{guix-daemon} is configured to save compressed build logs, as
is the case by default (@pxref{Aufruf des guix-daemon}), @code{/log} URLs
return the compressed log as-is, with an appropriate @code{Content-Type}
and/or @code{Content-Encoding} header.  We recommend running
@command{guix-daemon} with @code{--log-compression=gzip} since Web browsers
can automatically decompress it, which is not the case with bzip2
compression.

The following options are available:

@table @code
@item --port=@var{port}
@itemx -p @var{port}
Listen for HTTP requests on @var{port}.

@item --listen=@var{host}
Listen on the network interface for @var{host}.  The default is to accept
connections from any interface.

@item --user=@var{user}
@itemx -u @var{user}
Change privileges to @var{user} as soon as possible---i.e., once the server
socket is open and the signing key has been read.

@item --compression[=@var{level}]
@itemx -C [@var{level}]
Compress data using the given @var{level}.  When @var{level} is zero,
disable compression.  The range 1 to 9 corresponds to different gzip
compression levels: 1 is the fastest, and 9 is the best (CPU-intensive).
The default is 3.

Unless @option{--cache} is used, compression occurs on the fly and the
compressed streams are not cached.  Thus, to reduce load on the machine that
runs @command{guix publish}, it may be a good idea to choose a low
compression level, to run @command{guix publish} behind a caching proxy, or
to use @option{--cache}.  Using @option{--cache} has the advantage that it
allows @command{guix publish} to add @code{Content-Length} HTTP header to
its responses.

@item --cache=@var{directory}
@itemx -c @var{directory}
Cache archives and meta-data (@code{.narinfo} URLs) to @var{directory} and
only serve archives that are in cache.

When this option is omitted, archives and meta-data are created on-the-fly.
This can reduce the available bandwidth, especially when compression is
enabled, since this may become CPU-bound.  Another drawback of the default
mode is that the length of archives is not known in advance, so
@command{guix publish} does not add a @code{Content-Length} HTTP header to
its responses, which in turn prevents clients from knowing the amount of
data being downloaded.

Conversely, when @option{--cache} is used, the first request for a store
item (@i{via} a @code{.narinfo} URL) returns 404 and triggers a background
process to @dfn{bake} the archive---computing its @code{.narinfo} and
compressing the archive, if needed.  Once the archive is cached in
@var{directory}, subsequent requests succeed and are served directly from
the cache, which guarantees that clients get the best possible bandwidth.

The ``baking'' process is performed by worker threads.  By default, one
thread per CPU core is created, but this can be customized.  See
@option{--workers} below.

When @option{--ttl} is used, cached entries are automatically deleted when
they have expired.

@item --workers=@var{N}
When @option{--cache} is used, request the allocation of @var{N} worker
threads to ``bake'' archives.

@item --ttl=@var{ttl}
Produce @code{Cache-Control} HTTP headers that advertise a time-to-live
(TTL) of @var{ttl}.  @var{ttl} must denote a duration: @code{5d} means 5
days, @code{1m} means 1 month, and so on.

This allows the user's Guix to keep substitute information in cache for
@var{ttl}.  However, note that @code{guix publish} does not itself guarantee
that the store items it provides will indeed remain available for as long as
@var{ttl}.

Additionally, when @option{--cache} is used, cached entries that have not
been accessed for @var{ttl} and that no longer have a corresponding item in
the store, may be deleted.

@item --nar-path=@var{path}
Use @var{path} as the prefix for the URLs of ``nar'' files (@pxref{Aufruf von guix archive, normalized archives}).

By default, nars are served at a URL such as
@code{/nar/gzip/@dots{}-coreutils-8.25}.  This option allows you to change
the @code{/nar} part to @var{path}.

@item --public-key=@var{file}
@itemx --private-key=@var{file}
Use the specific @var{file}s as the public/private key pair used to sign the
store items being published.

The files must correspond to the same key pair (the private key is used for
signing and the public key is merely advertised in the signature metadata).
They must contain keys in the canonical s-expression format as produced by
@command{guix archive --generate-key} (@pxref{Aufruf von guix archive}).  By
default, @file{/etc/guix/signing-key.pub} and
@file{/etc/guix/signing-key.sec} are used.

@item --repl[=@var{port}]
@itemx -r [@var{port}]
Spawn a Guile REPL server (@pxref{REPL Servers,,, guile, GNU Guile Reference
Manual}) on @var{port} (37146 by default).  This is used primarily for
debugging a running @command{guix publish} server.
@end table

Enabling @command{guix publish} on a GuixSD system is a one-liner: just
instantiate a @code{guix-publish-service-type} service in the
@code{services} field of the @code{operating-system} declaration
(@pxref{guix-publish-service-type, @code{guix-publish-service-type}}).

If you are instead running Guix on a ``foreign distro'', follow these
instructions:”

@itemize
@item
If your host distro uses the systemd init system:

@example
# ln -s ~root/.guix-profile/lib/systemd/system/guix-publish.service \
        /etc/systemd/system/
# systemctl start guix-publish && systemctl enable guix-publish
@end example

@item
Wenn Ihre Wirts-Distribution als »init«-System Upstart verwendet:

@example
# ln -s ~root/.guix-profile/lib/upstart/system/guix-publish.conf /etc/init/
# start guix-publish
@end example

@item
Otherwise, proceed similarly with your distro's init system.
@end itemize

@node Aufruf von guix challenge
@section Invoking @command{guix challenge}

@cindex Reproduzierbare Erstellungen
@cindex verifiable builds
@cindex @command{guix challenge}
@cindex challenge
Do the binaries provided by this server really correspond to the source code
it claims to build? Is a package build process deterministic? These are the
questions the @command{guix challenge} command attempts to answer.

The former is obviously an important question: Before using a substitute
server (@pxref{Substitute}), one had better @emph{verify} that it provides
the right binaries, and thus @emph{challenge} it.  The latter is what
enables the former: If package builds are deterministic, then independent
builds of the package should yield the exact same result, bit for bit; if a
server provides a binary different from the one obtained locally, it may be
either corrupt or malicious.

We know that the hash that shows up in @file{/gnu/store} file names is the
hash of all the inputs of the process that built the file or
directory---compilers, libraries, build scripts,
etc. (@pxref{Einführung}).  Assuming deterministic build processes, one
store file name should map to exactly one build output.  @command{guix
challenge} checks whether there is, indeed, a single mapping by comparing
the build outputs of several independent builds of any given store item.

The command output looks like this:

@smallexample
$ guix challenge --substitute-urls="https://hydra.gnu.org https://guix.example.org"
updating list of substitutes from 'https://hydra.gnu.org'... 100.0%
updating list of substitutes from 'https://guix.example.org'... 100.0%
/gnu/store/@dots{}-openssl-1.0.2d contents differ:
  local hash: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
  https://hydra.gnu.org/nar/@dots{}-openssl-1.0.2d: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
  https://guix.example.org/nar/@dots{}-openssl-1.0.2d: 1zy4fmaaqcnjrzzajkdn3f5gmjk754b43qkq47llbyak9z0qjyim
/gnu/store/@dots{}-git-2.5.0 contents differ:
  local hash: 00p3bmryhjxrhpn2gxs2fy0a15lnip05l97205pgbk5ra395hyha
  https://hydra.gnu.org/nar/@dots{}-git-2.5.0: 069nb85bv4d4a6slrwjdy8v1cn4cwspm3kdbmyb81d6zckj3nq9f
  https://guix.example.org/nar/@dots{}-git-2.5.0: 0mdqa9w1p6cmli6976v4wi0sw9r4p5prkj7lzfd1877wk11c9c73
/gnu/store/@dots{}-pius-2.1.1 contents differ:
  local hash: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
  https://hydra.gnu.org/nar/@dots{}-pius-2.1.1: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
  https://guix.example.org/nar/@dots{}-pius-2.1.1: 1cy25x1a4fzq5rk0pmvc8xhwyffnqz95h2bpvqsz2mpvlbccy0gs

@dots{}

6,406 store items were analyzed:
  - 4,749 (74.1%) were identical
  - 525 (8.2%) differed
  - 1,132 (17.7%) were inconclusive
@end smallexample

@noindent
In this example, @command{guix challenge} first scans the store to determine
the set of locally-built derivations---as opposed to store items that were
downloaded from a substitute server---and then queries all the substitute
servers.  It then reports those store items for which the servers obtained a
result different from the local build.

@cindex non-determinism, in package builds
As an example, @code{guix.example.org} always gets a different answer.
Conversely, @code{hydra.gnu.org} agrees with local builds, except in the
case of Git.  This might indicate that the build process of Git is
non-deterministic, meaning that its output varies as a function of various
things that Guix does not fully control, in spite of building packages in
isolated environments (@pxref{Funktionalitäten}).  Most common sources of
non-determinism include the addition of timestamps in build results, the
inclusion of random numbers, and directory listings sorted by inode number.
See @uref{https://reproducible-builds.org/docs/}, for more information.

To find out what is wrong with this Git binary, we can do something along
these lines (@pxref{Aufruf von guix archive}):

@example
$ wget -q -O - https://hydra.gnu.org/nar/@dots{}-git-2.5.0 \
   | guix archive -x /tmp/git
$ diff -ur --no-dereference /gnu/store/@dots{}-git.2.5.0 /tmp/git
@end example

This command shows the difference between the files resulting from the local
build, and the files resulting from the build on @code{hydra.gnu.org}
(@pxref{Overview, Comparing and Merging Files,, diffutils, Comparing and
Merging Files}).  The @command{diff} command works great for text files.
When binary files differ, a better option is @uref{https://diffoscope.org/,
Diffoscope}, a tool that helps visualize differences for all kinds of files.

Once you have done that work, you can tell whether the differences are due
to a non-deterministic build process or to a malicious server.  We try hard
to remove sources of non-determinism in packages to make it easier to verify
substitutes, but of course, this is a process that involves not just Guix,
but a large part of the free software community.  In the meantime,
@command{guix challenge} is one tool to help address the problem.

If you are writing packages for Guix, you are encouraged to check whether
@code{hydra.gnu.org} and other substitute servers obtain the same build
result as you did with:

@example
$ guix challenge @var{package}
@end example

@noindent
where @var{package} is a package specification such as @code{guile@@2.0} or
@code{glibc:debug}.

The general syntax is:

@example
guix challenge @var{options} [@var{packages}@dots{}]
@end example

When a difference is found between the hash of a locally-built item and that
of a server-provided substitute, or among substitutes provided by different
servers, the command displays it as in the example above and its exit code
is 2 (other non-zero exit codes denote other kinds of errors.)

The one option that matters is:

@table @code

@item --substitute-urls=@var{URLs}
Consider @var{urls} the whitespace-separated list of substitute source URLs
to compare to.

@item --verbose
@itemx -v
Show details about matches (identical contents) in addition to information
about mismatches.

@end table

@node Aufruf von guix copy
@section Invoking @command{guix copy}

@cindex copy, of store items, over SSH
@cindex SSH, copy of store items
@cindex sharing store items across machines
@cindex transferring store items across machines
The @command{guix copy} command copies items from the store of one machine
to that of another machine over a secure shell (SSH)
connection@footnote{This command is available only when Guile-SSH was
found.  @xref{Voraussetzungen}, for details.}.  For example, the following
command copies the @code{coreutils} package, the user's profile, and all
their dependencies over to @var{host}, logged in as @var{user}:

@example
guix copy --to=@var{user}@@@var{host} \
          coreutils `readlink -f ~/.guix-profile`
@end example

If some of the items to be copied are already present on @var{host}, they
are not actually sent.

The command below retrieves @code{libreoffice} and @code{gimp} from
@var{host}, assuming they are available there:

@example
guix copy --from=@var{host} libreoffice gimp
@end example

The SSH connection is established using the Guile-SSH client, which is
compatible with OpenSSH: it honors @file{~/.ssh/known_hosts} and
@file{~/.ssh/config}, and uses the SSH agent for authentication.

The key used to sign items that are sent must be accepted by the remote
machine.  Likewise, the key used by the remote machine to sign items you are
retrieving must be in @file{/etc/guix/acl} so it is accepted by your own
daemon.  @xref{Aufruf von guix archive}, for more information about store item
authentication.

The general syntax is:

@example
guix copy [--to=@var{spec}|--from=@var{spec}] @var{items}@dots{}
@end example

You must always specify one of the following options:

@table @code
@item --to=@var{spec}
@itemx --from=@var{spec}
Specify the host to send to or receive from.  @var{spec} must be an SSH spec
such as @code{example.org}, @code{charlie@@example.org}, or
@code{charlie@@example.org:2222}.
@end table

The @var{items} can be either package names, such as @code{gimp}, or store
items, such as @file{/gnu/store/@dots{}-idutils-4.6}.

When specifying the name of a package to send, it is first built if needed,
unless @option{--dry-run} was specified.  Common build options are supported
(@pxref{Gemeinsame Erstellungsoptionen}).


@node Aufruf von guix container
@section Invoking @command{guix container}
@cindex container
@cindex @command{guix container}
@quotation Anmerkung
As of version @value{VERSION}, this tool is experimental.  The interface is
subject to radical change in the future.
@end quotation

The purpose of @command{guix container} is to manipulate processes running
within an isolated environment, commonly known as a ``container'', typically
created by the @command{guix environment} (@pxref{Aufruf von guix environment}) and @command{guix system container} (@pxref{Aufruf von guix system}) commands.

The general syntax is:

@example
guix container @var{action} @var{options}@dots{}
@end example

@var{action} specifies the operation to perform with a container, and
@var{options} specifies the context-specific arguments for the action.

The following actions are available:

@table @code
@item exec
Execute a command within the context of a running container.

The syntax is:

@example
guix container exec @var{pid} @var{program} @var{arguments}@dots{}
@end example

@var{pid} specifies the process ID of the running container.  @var{program}
specifies an executable file name within the root file system of the
container.  @var{arguments} are the additional options that will be passed
to @var{program}.

The following command launches an interactive login shell inside a GuixSD
container, started by @command{guix system container}, and whose process ID
is 9001:

@example
guix container exec 9001 /run/current-system/profile/bin/bash --login
@end example

Note that the @var{pid} cannot be the parent process of a container.  It
must be PID 1 of the container or one of its child processes.

@end table

@node Aufruf von guix weather
@section Invoking @command{guix weather}

Occasionally you're grumpy because substitutes are lacking and you end up
building packages by yourself (@pxref{Substitute}).  The @command{guix
weather} command reports on substitute availability on the specified servers
so you can have an idea of whether you'll be grumpy today.  It can sometimes
be useful info as a user, but it is primarily useful to people running
@command{guix publish} (@pxref{Aufruf von guix publish}).

@cindex statistics, for substitutes
@cindex availability of substitutes
@cindex substitute availability
@cindex weather, substitute availability
Here's a sample run:

@example
$ guix weather --substitute-urls=https://guix.example.org
computing 5,872 package derivations for x86_64-linux...
looking for 6,128 store items on https://guix.example.org..
updating list of substitutes from 'https://guix.example.org'... 100.0%
https://guix.example.org
  43.4% substitutes available (2,658 out of 6,128)
  7,032.5 MiB of nars (compressed)
  19,824.2 MiB on disk (uncompressed)
  0.030 seconds per request (182.9 seconds in total)
  33.5 requests per second

  9.8% (342 out of 3,470) of the missing items are queued
  867 queued builds
      x86_64-linux: 518 (59.7%)
      i686-linux: 221 (25.5%)
      aarch64-linux: 128 (14.8%)
  build rate: 23.41 builds per hour
      x86_64-linux: 11.16 builds per hour
      i686-linux: 6.03 builds per hour
      aarch64-linux: 6.41 builds per hour
@end example

@cindex continuous integration, statistics
As you can see, it reports the fraction of all the packages for which
substitutes are available on the server---regardless of whether substitutes
are enabled, and regardless of whether this server's signing key is
authorized.  It also reports the size of the compressed archives (``nars'')
provided by the server, the size the corresponding store items occupy in the
store (assuming deduplication is turned off), and the server's throughput.
The second part gives continuous integration (CI) statistics, if the server
supports it.

To achieve that, @command{guix weather} queries over HTTP(S) meta-data
(@dfn{narinfos}) for all the relevant store items.  Like @command{guix
challenge}, it ignores signatures on those substitutes, which is innocuous
since the command only gathers statistics and cannot install those
substitutes.

Among other things, it is possible to query specific system types and
specific package sets.  The available options are listed below.

@table @code
@item --substitute-urls=@var{URLs}
@var{urls} is the space-separated list of substitute server URLs to query.
When this option is omitted, the default set of substitute servers is
queried.

@item --system=@var{System}
@itemx -s @var{system}
Query substitutes for @var{system}---e.g., @code{aarch64-linux}.  This
option can be repeated, in which case @command{guix weather} will query
substitutes for several system types.

@item --manifest=@var{Datei}
Instead of querying substitutes for all the packages, only ask for those
specified in @var{file}.  @var{file} must contain a @dfn{manifest}, as with
the @code{-m} option of @command{guix package} (@pxref{Aufruf von guix package}).
@end table

@node Invoking guix processes
@section Invoking @command{guix processes}

The @command{guix processes} command can be useful to developers and system
administrators, especially on multi-user machines and on build farms: it
lists the current sessions (connections to the daemon), as well as
information about the processes involved@footnote{Remote sessions, when
@command{guix-daemon} is started with @option{--listen} specifying a TCP
endpoint, are @emph{not} listed.}.  Here's an example of the information it
returns:

@example
$ sudo guix processes
SessionPID: 19002
ClientPID: 19090
ClientCommand: guix environment --ad-hoc python

SessionPID: 19402
ClientPID: 19367
ClientCommand: guix publish -u guix-publish -p 3000 -C 9 @dots{}

SessionPID: 19444
ClientPID: 19419
ClientCommand: cuirass --cache-directory /var/cache/cuirass @dots{}
LockHeld: /gnu/store/@dots{}-perl-ipc-cmd-0.96.lock
LockHeld: /gnu/store/@dots{}-python-six-bootstrap-1.11.0.lock
LockHeld: /gnu/store/@dots{}-libjpeg-turbo-2.0.0.lock
ChildProcess: 20495: guix offload x86_64-linux 7200 1 28800
ChildProcess: 27733: guix offload x86_64-linux 7200 1 28800
ChildProcess: 27793: guix offload x86_64-linux 7200 1 28800
@end example

In this example we see that @command{guix-daemon} has three clients:
@command{guix environment}, @command{guix publish}, and the Cuirass
continuous integration tool; their process identifier (PID) is given by the
@code{ClientPID} field.  The @code{SessionPID} field gives the PID of the
@command{guix-daemon} sub-process of this particular session.

The @code{LockHeld} fields show which store items are currently locked by
this session, which corresponds to store items being built or substituted
(the @code{LockHeld} field is not displayed when @command{guix processes} is
not running as root.)  Last, by looking at the @code{ChildProcess} field, we
understand that these three builds are being offloaded (@pxref{Auslagern des Daemons einrichten}).

The output is in Recutils format so we can use the handy @command{recsel}
command to select sessions of interest (@pxref{Selection Expressions,,,
recutils, GNU recutils manual}).  As an example, the command shows the
command line and PID of the client that triggered the build of a Perl
package:

@example
$ sudo guix processes | \
    recsel -p ClientPID,ClientCommand -e 'LockHeld ~ "perl"'
ClientPID: 19419
ClientCommand: cuirass --cache-directory /var/cache/cuirass @dots{}
@end example

@c *********************************************************************
@node GNU-Distribution
@chapter GNU-Distribution

@cindex Guix System Distribution
@cindex GuixSD
Guix comes with a distribution of the GNU system consisting entirely of free
software@footnote{The term ``free'' here refers to the
@url{http://www.gnu.org/philosophy/free-sw.html,freedom provided to users of
that software}.}.  The distribution can be installed on its own
(@pxref{Systeminstallation}), but it is also possible to install Guix as a
package manager on top of an installed GNU/Linux system
(@pxref{Installation}).  To distinguish between the two, we refer to the
standalone distribution as the Guix System Distribution, or GuixSD.

The distribution provides core GNU packages such as GNU libc, GCC, and
Binutils, as well as many GNU and non-GNU applications.  The complete list
of available packages can be browsed
@url{http://www.gnu.org/software/guix/packages,on-line} or by running
@command{guix package} (@pxref{Aufruf von guix package}):

@example
guix package --list-available
@end example

Our goal is to provide a practical 100% free software distribution of
Linux-based and other variants of GNU, with a focus on the promotion and
tight integration of GNU components, and an emphasis on programs and tools
that help users exert that freedom.

Packages are currently available on the following platforms:

@table @code

@item x86_64-linux
Intel/AMD @code{x86_64} architecture, Linux-Libre kernel;

@item i686-linux
Intel 32-bit architecture (IA32), Linux-Libre kernel;

@item armhf-linux
ARMv7-A architecture with hard float, Thumb-2 and NEON, using the EABI
hard-float application binary interface (ABI), and Linux-Libre kernel.

@item aarch64-linux
little-endian 64-bit ARMv8-A processors, Linux-Libre kernel.  This is
currently in an experimental stage, with limited support.
@xref{Mitwirken}, for how to help!

@item mips64el-linux
little-endian 64-bit MIPS processors, specifically the Loongson series, n32
ABI, and Linux-Libre kernel.

@end table

GuixSD itself is currently only available on @code{i686} and @code{x86_64}.

@noindent
For information on porting to other architectures or kernels,
@pxref{Portierung}.

@menu
* Systeminstallation::       Das ganze Betriebssystem installieren.
* Systemkonfiguration::      Das Betriebssystem konfigurieren.
* Dokumentation::            Wie man Nutzerhandbücher von Software liest.
* Dateien zur Fehlersuche installieren::  Womit man seinen Debugger 
                                            füttert.
* Sicherheitsaktualisierungen::  Sicherheits-Patches schnell einspielen.
* Paketmodule::              Pakete aus Sicht des Programmierers.
* Paketrichtlinien::         Die Distribution wachsen lassen.
* Bootstrapping::            GNU/Linux von Grund auf selbst erstellen.
* Portierung::               Guix auf andere Plattformen und Kernels 
                               bringen.
@end menu

Building this distribution is a cooperative effort, and you are invited to
join! @xref{Mitwirken}, for information about how you can help.

@node Systeminstallation
@section Systeminstallation

@cindex installing GuixSD
@cindex Guix System Distribution
This section explains how to install the Guix System Distribution (GuixSD)
on a machine.  The Guix package manager can also be installed on top of a
running GNU/Linux system, @pxref{Installation}.

@ifinfo
@quotation Anmerkung
@c This paragraph is for people reading this from tty2 of the
@c installation image.
You are reading this documentation with an Info reader.  For details on how
to use it, hit the @key{RET} key (``return'' or ``enter'') on the link that
follows: @pxref{Top, Info reader,, info-stnd, Stand-alone GNU Info}.  Hit
@kbd{l} afterwards to come back here.

Alternately, run @command{info info} in another tty to keep the manual
available.
@end quotation
@end ifinfo

@menu
* Einschränkungen::         Was Sie erwarten dürfen.
* Hardware-Überlegungen::   Unterstützte Hardware.
* Installation von USB-Stick oder DVD::  Das Installationsmedium 
                                           vorbereiten.
* Vor der Installation::     Netzwerkanbindung, Partitionierung etc.
* Fortfahren mit der Installation::  Die Hauptsache.
* GuixSD in einer VM installieren::  Ein GuixSD-Spielplatz.
* Ein Abbild zur Installation erstellen::  Wie ein solches entsteht.
@end menu

@node Einschränkungen
@subsection Einschränkungen

As of version @value{VERSION}, the Guix System Distribution (GuixSD) is not
production-ready.  It may contain bugs and lack important features.  Thus,
if you are looking for a stable production system that respects your freedom
as a computer user, a good solution at this point is to consider
@url{http://www.gnu.org/distros/free-distros.html, one of the more
established GNU/Linux distributions}.  We hope you can soon switch to the
GuixSD without fear, of course.  In the meantime, you can also keep using
your distribution and try out the package manager on top of it
(@pxref{Installation}).

Before you proceed with the installation, be aware of the following
noteworthy limitations applicable to version @value{VERSION}:

@itemize
@item
The installation process does not include a graphical user interface and
requires familiarity with GNU/Linux (see the following subsections to get a
feel of what that means.)

@item
Support for the Logical Volume Manager (LVM) is missing.

@item
More and more system services are provided (@pxref{Dienste}), but some may
be missing.

@item
More than 7,500 packages are available, but you might occasionally find that
a useful package is missing.

@item
GNOME, Xfce, LXDE, and Enlightenment are available (@pxref{Desktop-Dienste}), as well as a number of X11 window managers.  However, some
graphical applications may be missing, as well as KDE.
@end itemize

You have been warned! But more than a disclaimer, this is an invitation to
report issues (and success stories!), and to join us in improving it.
@xref{Mitwirken}, for more info.


@node Hardware-Überlegungen
@subsection Hardware-Überlegungen

@cindex hardware support on GuixSD
GNU@tie{}GuixSD focuses on respecting the user's computing freedom.  It
builds around the kernel Linux-libre, which means that only hardware for
which free software drivers and firmware exist is supported.  Nowadays, a
wide range of off-the-shelf hardware is supported on GNU/Linux-libre---from
keyboards to graphics cards to scanners and Ethernet controllers.
Unfortunately, there are still areas where hardware vendors deny users
control over their own computing, and such hardware is not supported on
GuixSD.

@cindex WiFi, hardware support
One of the main areas where free drivers or firmware are lacking is WiFi
devices.  WiFi devices known to work include those using Atheros chips
(AR9271 and AR7010), which corresponds to the @code{ath9k} Linux-libre
driver, and those using Broadcom/AirForce chips (BCM43xx with Wireless-Core
Revision 5), which corresponds to the @code{b43-open} Linux-libre driver.
Free firmware exists for both and is available out-of-the-box on GuixSD, as
part of @var{%base-firmware} (@pxref{„operating-system“-Referenz,
@code{firmware}}).

@cindex RYF, Respects Your Freedom
The @uref{https://www.fsf.org/, Free Software Foundation} runs
@uref{https://www.fsf.org/ryf, @dfn{Respects Your Freedom}} (RYF), a
certification program for hardware products that respect your freedom and
your privacy and ensure that you have control over your device.  We
encourage you to check the list of RYF-certified devices.

Another useful resource is the @uref{https://www.h-node.org/, H-Node} web
site.  It contains a catalog of hardware devices with information about
their support in GNU/Linux.


@node Installation von USB-Stick oder DVD
@subsection Installation von USB-Stick oder DVD

An ISO-9660 installation image that can be written to a USB stick or burnt
to a DVD can be downloaded from
@indicateurl{https://alpha.gnu.org/gnu/guix/guixsd-install-@value{VERSION}.@var{system}.iso.xz},
where @var{system} is one of:

@table @code
@item x86_64-linux
for a GNU/Linux system on Intel/AMD-compatible 64-bit CPUs;

@item i686-linux
for a 32-bit GNU/Linux system on Intel-compatible CPUs.
@end table

@c start duplication of authentication part from ``Binary Installation''
Make sure to download the associated @file{.sig} file and to verify the
authenticity of the image against it, along these lines:

@example
$ wget https://alpha.gnu.org/gnu/guix/guixsd-install-@value{VERSION}.@var{system}.iso.xz.sig
$ gpg --verify guixsd-install-@value{VERSION}.@var{system}.iso.xz.sig
@end example

Falls dieser Befehl fehlschlägt, weil Sie nicht über den nötigen
öffentlichen Schlüssel verfügen, können Sie ihn mit diesem Befehl
importieren:

@example
$ gpg --keyserver pgp.mit.edu --recv-keys @value{OPENPGP-SIGNING-KEY-ID}
@end example

@noindent
@c end duplication
und den Befehl @code{gpg --verify} erneut ausführen.

This image contains the tools necessary for an installation.  It is meant to
be copied @emph{as is} to a large-enough USB stick or DVD.

@unnumberedsubsubsec Copying to a USB Stick

To copy the image to a USB stick, follow these steps:

@enumerate
@item
Decompress the image using the @command{xz} command:

@example
xz -d guixsd-install-@value{VERSION}.@var{system}.iso.xz
@end example

@item
Insert a USB stick of 1@tie{}GiB or more into your machine, and determine
its device name.  Assuming that the USB stick is known as @file{/dev/sdX},
copy the image with:

@example
dd if=guixsd-install-@value{VERSION}.x86_64-linux.iso of=/dev/sdX
sync
@end example

Access to @file{/dev/sdX} usually requires root privileges.
@end enumerate

@unnumberedsubsubsec Burning on a DVD

To copy the image to a DVD, follow these steps:

@enumerate
@item
Decompress the image using the @command{xz} command:

@example
xz -d guixsd-install-@value{VERSION}.@var{system}.iso.xz
@end example

@item
Insert a blank DVD into your machine, and determine its device name.
Assuming that the DVD drive is known as @file{/dev/srX}, copy the image
with:

@example
growisofs -dvd-compat -Z /dev/srX=guixsd-install-@value{VERSION}.x86_64.iso
@end example

Access to @file{/dev/srX} usually requires root privileges.
@end enumerate

@unnumberedsubsubsec Booting

Once this is done, you should be able to reboot the system and boot from the
USB stick or DVD.  The latter usually requires you to get in the BIOS or
UEFI boot menu, where you can choose to boot from the USB stick.

@xref{GuixSD in einer VM installieren}, if, instead, you would like to install
GuixSD in a virtual machine (VM).


@node Vor der Installation
@subsection Vor der Installation

Once you have successfully booted your computer using the installation
medium, you should end up with a root prompt.  Several console TTYs are
configured and can be used to run commands as root.  TTY2 shows this
documentation, browsable using the Info reader commands (@pxref{Top,,,
info-stnd, Stand-alone GNU Info}).  The installation system runs the GPM
mouse daemon, which allows you to select text with the left mouse button and
to paste it with the middle button.

@quotation Anmerkung
Installation requires access to the Internet so that any missing
dependencies of your system configuration can be downloaded.  See the
``Networking'' section below.
@end quotation

The installation system includes many common tools needed for this task.
But it is also a full-blown GuixSD system, which means that you can install
additional packages, should you need it, using @command{guix package}
(@pxref{Aufruf von guix package}).

@subsubsection Keyboard Layout

@cindex keyboard layout
The installation image uses the US qwerty keyboard layout.  If you want to
change it, you can use the @command{loadkeys} command.  For example, the
following command selects the Dvorak keyboard layout:

@example
loadkeys dvorak
@end example

See the files under @file{/run/current-system/profile/share/keymaps} for a
list of available keyboard layouts.  Run @command{man loadkeys} for more
information.

@subsubsection Networking

Run the following command to see what your network interfaces are called:

@example
ifconfig -a
@end example

@noindent
@dots{} or, using the GNU/Linux-specific @command{ip} command:

@example
ip a
@end example

@c http://cgit.freedesktop.org/systemd/systemd/tree/src/udev/udev-builtin-net_id.c#n20
Wired interfaces have a name starting with @samp{e}; for example, the
interface corresponding to the first on-board Ethernet controller is called
@samp{eno1}.  Wireless interfaces have a name starting with @samp{w}, like
@samp{w1p2s0}.

@table @asis
@item Wired connection
To configure a wired network run the following command, substituting
@var{interface} with the name of the wired interface you want to use.

@example
ifconfig @var{interface} up
@end example

@item Wireless connection
@cindex wireless
@cindex WiFi
To configure wireless networking, you can create a configuration file for
the @command{wpa_supplicant} configuration tool (its location is not
important) using one of the available text editors such as @command{nano}:

@example
nano wpa_supplicant.conf
@end example

As an example, the following stanza can go to this file and will work for
many wireless networks, provided you give the actual SSID and passphrase for
the network you are connecting to:

@example
network=@{
  ssid="@var{my-ssid}"
  key_mgmt=WPA-PSK
  psk="the network's secret passphrase"
@}
@end example

Start the wireless service and run it in the background with the following
command (substitute @var{interface} with the name of the network interface
you want to use):

@example
wpa_supplicant -c wpa_supplicant.conf -i @var{interface} -B
@end example

Run @command{man wpa_supplicant} for more information.
@end table

@cindex DHCP
At this point, you need to acquire an IP address.  On a network where IP
addresses are automatically assigned @i{via} DHCP, you can run:

@example
dhclient -v @var{interface}
@end example

Try to ping a server to see if networking is up and running:

@example
ping -c 3 gnu.org
@end example

Setting up network access is almost always a requirement because the image
does not contain all the software and tools that may be needed.

@cindex installing over SSH
If you want to, you can continue the installation remotely by starting an
SSH server:

@example
herd start ssh-daemon
@end example

Make sure to either set a password with @command{passwd}, or configure
OpenSSH public key authentication before logging in.

@subsubsection Disk Partitioning

Unless this has already been done, the next step is to partition, and then
format the target partition(s).

The installation image includes several partitioning tools, including Parted
(@pxref{Overview,,, parted, GNU Parted User Manual}), @command{fdisk}, and
@command{cfdisk}.  Run it and set up your disk with the partition layout you
want:

@example
cfdisk
@end example

If your disk uses the GUID Partition Table (GPT) format and you plan to
install BIOS-based GRUB (which is the default), make sure a BIOS Boot
Partition is available (@pxref{BIOS installation,,, grub, GNU GRUB manual}).

@cindex EFI, installation
@cindex UEFI, installation
@cindex ESP, EFI system partition
If you instead wish to use EFI-based GRUB, a FAT32 @dfn{EFI System
Partition} (ESP) is required.  This partition should be mounted at
@file{/boot/efi} and must have the @code{esp} flag set.  E.g., for
@command{parted}:

@example
parted /dev/sda set 1 esp on
@end example

@quotation Anmerkung
@vindex grub-bootloader
@vindex grub-efi-bootloader
Unsure whether to use EFI- or BIOS-based GRUB? If the directory
@file{/sys/firmware/efi} exists in the installation image, then you should
probably perform an EFI installation, using @code{grub-efi-bootloader}.
Otherwise you should use the BIOS-based GRUB, known as
@code{grub-bootloader}.  @xref{Bootloader-Konfiguration}, for more info on
bootloaders.
@end quotation

Once you are done partitioning the target hard disk drive, you have to
create a file system on the relevant partition(s)@footnote{Currently GuixSD
only supports ext4 and btrfs file systems.  In particular, code that reads
file system UUIDs and labels only works for these file system types.}.  For
the ESP, if you have one and assuming it is @file{/dev/sda1}, run:

@example
mkfs.fat -F32 /dev/sda1
@end example

Preferably, assign file systems a label so that you can easily and reliably
refer to them in @code{file-system} declarations (@pxref{Dateisysteme}).
This is typically done using the @code{-L} option of @command{mkfs.ext4} and
related commands.  So, assuming the target root partition lives at
@file{/dev/sda2}, a file system with the label @code{my-root} can be created
with:

@example
mkfs.ext4 -L my-root /dev/sda2
@end example

@cindex encrypted disk
If you are instead planning to encrypt the root partition, you can use the
Cryptsetup/LUKS utilities to do that (see @inlinefmtifelse{html,
@uref{https://linux.die.net/man/8/cryptsetup, @code{man cryptsetup}},
@code{man cryptsetup}} for more information.)  Assuming you want to store
the root partition on @file{/dev/sda2}, the command sequence would be along
these lines:

@example
cryptsetup luksFormat /dev/sda2
cryptsetup open --type luks /dev/sda2 my-partition
mkfs.ext4 -L my-root /dev/mapper/my-partition
@end example

Once that is done, mount the target file system under @file{/mnt} with a
command like (again, assuming @code{my-root} is the label of the root file
system):

@example
mount LABEL=my-root /mnt
@end example

Also mount any other file systems you would like to use on the target system
relative to this path.  If you have @file{/boot} on a separate partition for
example, mount it at @file{/mnt/boot} now so it is found by @code{guix
system init} afterwards.

Finally, if you plan to use one or more swap partitions (@pxref{Memory
Concepts, swap space,, libc, The GNU C Library Reference Manual}), make sure
to initialize them with @command{mkswap}.  Assuming you have one swap
partition on @file{/dev/sda3}, you would run:

@example
mkswap /dev/sda3
swapon /dev/sda3
@end example

Alternatively, you may use a swap file.  For example, assuming that in the
new system you want to use the file @file{/swapfile} as a swap file, you
would run@footnote{This example will work for many types of file systems
(e.g., ext4).  However, for copy-on-write file systems (e.g., btrfs), the
required steps may be different.  For details, see the manual pages for
@command{mkswap} and @command{swapon}.}:

@example
# This is 10 GiB of swap space.  Adjust "count" to change the size.
dd if=/dev/zero of=/mnt/swapfile bs=1MiB count=10240
# For security, make the file readable and writable only by root.
chmod 600 /mnt/swapfile
mkswap /mnt/swapfile
swapon /mnt/swapfile
@end example

Note that if you have encrypted the root partition and created a swap file
in its file system as described above, then the encryption also protects the
swap file, just like any other file in that file system.

@node Fortfahren mit der Installation
@subsection Fortfahren mit der Installation

With the target partitions ready and the target root mounted on @file{/mnt},
we're ready to go.  First, run:

@example
herd start cow-store /mnt
@end example

This makes @file{/gnu/store} copy-on-write, such that packages added to it
during the installation phase are written to the target disk on @file{/mnt}
rather than kept in memory.  This is necessary because the first phase of
the @command{guix system init} command (see below) entails downloads or
builds to @file{/gnu/store} which, initially, is an in-memory file system.

Next, you have to edit a file and provide the declaration of the operating
system to be installed.  To that end, the installation system comes with
three text editors.  We recommend GNU nano (@pxref{Top,,, nano, GNU nano
Manual}), which supports syntax highlighting and parentheses matching; other
editors include GNU Zile (an Emacs clone), and nvi (a clone of the original
BSD @command{vi} editor).  We strongly recommend storing that file on the
target root file system, say, as @file{/mnt/etc/config.scm}.  Failing to do
that, you will have lost your configuration file once you have rebooted into
the newly-installed system.

@xref{Das Konfigurationssystems nutzen}, for an overview of the configuration
file.  The example configurations discussed in that section are available
under @file{/etc/configuration} in the installation image.  Thus, to get
started with a system configuration providing a graphical display server (a
``desktop'' system), you can run something along these lines:

@example
# mkdir /mnt/etc
# cp /etc/configuration/desktop.scm /mnt/etc/config.scm
# nano /mnt/etc/config.scm
@end example

You should pay attention to what your configuration file contains, and in
particular:

@itemize
@item
Make sure the @code{bootloader-configuration} form refers to the target you
want to install GRUB on.  It should mention @code{grub-bootloader} if you
are installing GRUB in the legacy way, or @code{grub-efi-bootloader} for
newer UEFI systems.  For legacy systems, the @code{target} field names a
device, like @code{/dev/sda}; for UEFI systems it names a path to a mounted
EFI partition, like @code{/boot/efi}, and do make sure the path is actually
mounted.

@item
Be sure that your file system labels match the value of their respective
@code{device} fields in your @code{file-system} configuration, assuming your
@code{file-system} configuration uses the @code{file-system-label} procedure
in its @code{device} field.

@item
If there are encrypted or RAID partitions, make sure to add a
@code{mapped-devices} field to describe them (@pxref{Abgebildete Geräte}).
@end itemize

Once you are done preparing the configuration file, the new system must be
initialized (remember that the target root file system is mounted under
@file{/mnt}):

@example
guix system init /mnt/etc/config.scm /mnt
@end example

@noindent
This copies all the necessary files and installs GRUB on @file{/dev/sdX},
unless you pass the @option{--no-bootloader} option.  For more information,
@pxref{Aufruf von guix system}.  This command may trigger downloads or builds
of missing packages, which can take some time.

Once that command has completed---and hopefully succeeded!---you can run
@command{reboot} and boot into the new system.  The @code{root} password in
the new system is initially empty; other users' passwords need to be
initialized by running the @command{passwd} command as @code{root}, unless
your configuration specifies otherwise (@pxref{user-account-password, user
account passwords}).

@cindex upgrading GuixSD
From then on, you can update GuixSD whenever you want by running
@command{guix pull} as @code{root} (@pxref{Aufruf von guix pull}), and then
running @command{guix system reconfigure} to build a new system generation
with the latest packages and services (@pxref{Aufruf von guix system}).  We
recommend doing that regularly so that your system includes the latest
security updates (@pxref{Sicherheitsaktualisierungen}).

Join us on @code{#guix} on the Freenode IRC network or on
@file{guix-devel@@gnu.org} to share your experience---good or not so good.

@node GuixSD in einer VM installieren
@subsection Installing GuixSD in a Virtual Machine

@cindex virtual machine, GuixSD installation
@cindex virtual private server (VPS)
@cindex VPS (virtual private server)
If you'd like to install GuixSD in a virtual machine (VM) or on a virtual
private server (VPS) rather than on your beloved machine, this section is
for you.

To boot a @uref{http://qemu.org/,QEMU} VM for installing GuixSD in a disk
image, follow these steps:

@enumerate
@item
First, retrieve and decompress the GuixSD installation image as described
previously (@pxref{Installation von USB-Stick oder DVD}).

@item
Create a disk image that will hold the installed system.  To make a
qcow2-formatted disk image, use the @command{qemu-img} command:

@example
qemu-img create -f qcow2 guixsd.img 50G
@end example

The resulting file will be much smaller than 50 GB (typically less than 1
MB), but it will grow as the virtualized storage device is filled up.

@item
Boot the USB installation image in an VM:

@example
qemu-system-x86_64 -m 1024 -smp 1 \
  -net user -net nic,model=virtio -boot menu=on \
  -drive file=guixsd-install-@value{VERSION}.@var{system}.iso \
  -drive file=guixsd.img
@end example

The ordering of the drives matters.

In the VM console, quickly press the @kbd{F12} key to enter the boot menu.
Then press the @kbd{2} key and the @kbd{RET} key to validate your selection.

@item
You're now root in the VM, proceed with the installation process.
@xref{Vor der Installation}, and follow the instructions.
@end enumerate

Once installation is complete, you can boot the system that's on your
@file{guixsd.img} image.  @xref{GuixSD in einer VM starten}, for how to do that.

@node Ein Abbild zur Installation erstellen
@subsection Ein Abbild zur Installation erstellen

@cindex installation image
The installation image described above was built using the @command{guix
system} command, specifically:

@example
guix system disk-image gnu/system/install.scm
@end example

Have a look at @file{gnu/system/install.scm} in the source tree, and see
also @ref{Aufruf von guix system} for more information about the installation
image.

@subsection Building the Installation Image for ARM Boards

Many ARM boards require a specific variant of the
@uref{http://www.denx.de/wiki/U-Boot/, U-Boot} bootloader.

If you build a disk image and the bootloader is not available otherwise (on
another boot drive etc), it's advisable to build an image that includes the
bootloader, specifically:

@example
guix system disk-image --system=armhf-linux -e '((@@ (gnu system install) os-with-u-boot) (@@ (gnu system install) installation-os) "A20-OLinuXino-Lime2")'
@end example

@code{A20-OLinuXino-Lime2} is the name of the board.  If you specify an
invalid board, a list of possible boards will be printed.

@node Systemkonfiguration
@section Systemkonfiguration

@cindex system configuration
The Guix System Distribution supports a consistent whole-system
configuration mechanism.  By that we mean that all aspects of the global
system configuration---such as the available system services, timezone and
locale settings, user accounts---are declared in a single place.  Such a
@dfn{system configuration} can be @dfn{instantiated}---i.e., effected.

@c Yes, we're talking of Puppet, Chef, & co. here.  ↑
One of the advantages of putting all the system configuration under the
control of Guix is that it supports transactional system upgrades, and makes
it possible to roll back to a previous system instantiation, should
something go wrong with the new one (@pxref{Funktionalitäten}).  Another advantage
is that it makes it easy to replicate the exact same configuration across
different machines, or at different points in time, without having to resort
to additional administration tools layered on top of the own tools of the
system.

This section describes this mechanism.  First we focus on the system
administrator's viewpoint---explaining how the system is configured and
instantiated.  Then we show how this mechanism can be extended, for instance
to support new system services.

@menu
* Das Konfigurationssystems nutzen::  Ihr GNU-System anpassen
* „operating-system“-Referenz::  Details der 
                                       Betriebssystem-Deklarationen.
* Dateisysteme::             Die Dateisystemeinbindungen konfigurieren.
* Abgebildete Geräte::      Zusatzverarbeitungsschritte für blockbasierte 
                               Geräte.
* Benutzerkonten::           Benutzerkonten festlegen.
* Locales::                  Sprach- und kulturelle 
                               Konventionseinstellungen.
* Dienste::                  Systemdienste festlegen.
* Setuid-Programme::         Programme mit Administratorrechten ausführen
* X.509-Zertifikate::        HTTPS-Server authentifizieren.
* Name Service Switch::      Den Name Service Switch von libc konfigurieren.
* Initiale RAM-Disk::        Linux-libre hochfahren.
* Bootloader-Konfiguration::  Den Bootloader konfigurieren.
* Aufruf von guix system::   Instanzierung einer Systemkonfiguration
* GuixSD in einer VM starten::  Wie man GuixSD in einer virtuellen Maschine 
                                  startet.
* Dienste definieren::       Neue Dienstdefinitionen hinzufügen.
@end menu

@node Das Konfigurationssystems nutzen
@subsection Das Konfigurationssystems nutzen

The operating system is configured by providing an @code{operating-system}
declaration in a file that can then be passed to the @command{guix system}
command (@pxref{Aufruf von guix system}).  A simple setup, with the default
system services, the default Linux-Libre kernel, initial RAM disk, and boot
loader looks like this:

@findex operating-system
@lisp
@include os-config-bare-bones.texi
@end lisp

This example should be self-describing.  Some of the fields defined above,
such as @code{host-name} and @code{bootloader}, are mandatory.  Others, such
as @code{packages} and @code{services}, can be omitted, in which case they
get a default value.

Below we discuss the effect of some of the most important fields
(@pxref{„operating-system“-Referenz}, for details about all the available
fields), and how to @dfn{instantiate} the operating system using
@command{guix system}.

@unnumberedsubsubsec Bootloader

@cindex legacy boot, on Intel machines
@cindex BIOS boot, on Intel machines
@cindex UEFI boot
@cindex EFI boot
The @code{bootloader} field describes the method that will be used to boot
your system.  Machines based on Intel processors can boot in ``legacy'' BIOS
mode, as in the example above.  However, more recent machines rely instead
on the @dfn{Unified Extensible Firmware Interface} (UEFI) to boot.  In that
case, the @code{bootloader} field should contain something along these
lines:

@example
(bootloader-configuration
  (bootloader grub-efi-bootloader)
  (target "/boot/efi"))
@end example

@xref{Bootloader-Konfiguration}, for more information on the available
configuration options.

@unnumberedsubsubsec Globally-Visible Packages

@vindex %base-packages
The @code{packages} field lists packages that will be globally visible on
the system, for all user accounts---i.e., in every user's @code{PATH}
environment variable---in addition to the per-user profiles (@pxref{Aufruf von guix package}).  The @var{%base-packages} variable provides all the tools
one would expect for basic user and administrator tasks---including the GNU
Core Utilities, the GNU Networking Utilities, the GNU Zile lightweight text
editor, @command{find}, @command{grep}, etc.  The example above adds
GNU@tie{}Screen and OpenSSH to those, taken from the @code{(gnu packages
screen)} and @code{(gnu packages ssh)} modules (@pxref{Paketmodule}).
The @code{(list package output)} syntax can be used to add a specific output
of a package:

@lisp
(use-modules (gnu packages))
(use-modules (gnu packages dns))

(operating-system
  ;; ...
  (packages (cons (list bind "utils")
                  %base-packages)))
@end lisp

@findex specification->package
Referring to packages by variable name, like @code{bind} above, has the
advantage of being unambiguous; it also allows typos and such to be
diagnosed right away as ``unbound variables''.  The downside is that one
needs to know which module defines which package, and to augment the
@code{use-package-modules} line accordingly.  To avoid that, one can use the
@code{specification->package} procedure of the @code{(gnu packages)} module,
which returns the best package for a given name or name and version:

@lisp
(use-modules (gnu packages))

(operating-system
  ;; ...
  (packages (append (map specification->package
                         '("tcpdump" "htop" "gnupg@@2.0"))
                    %base-packages)))
@end lisp

@unnumberedsubsubsec System Services

@cindex services
@vindex %base-services
The @code{services} field lists @dfn{system services} to be made available
when the system starts (@pxref{Dienste}).  The @code{operating-system}
declaration above specifies that, in addition to the basic services, we want
the @command{lshd} secure shell daemon listening on port 2222
(@pxref{Netzwerkdienste, @code{lsh-service}}).  Under the hood,
@code{lsh-service} arranges so that @code{lshd} is started with the right
command-line options, possibly with supporting configuration files generated
as needed (@pxref{Dienste definieren}).

@cindex customization, of services
@findex modify-services
Occasionally, instead of using the base services as is, you will want to
customize them.  To do this, use @code{modify-services} (@pxref{Service-Referenz, @code{modify-services}}) to modify the list.

For example, suppose you want to modify @code{guix-daemon} and Mingetty (the
console log-in) in the @var{%base-services} list (@pxref{Basisdienste,
@code{%base-services}}).  To do that, you can write the following in your
operating system declaration:

@lisp
(define %my-services
  ;; My very own list of services.
  (modify-services %base-services
    (guix-service-type config =>
                       (guix-configuration
                        (inherit config)
                        (use-substitutes? #f)
                        (extra-options '("--gc-keep-derivations"))))
    (mingetty-service-type config =>
                           (mingetty-configuration
                            (inherit config)))))

(operating-system
  ;; @dots{}
  (services %my-services))
@end lisp

This changes the configuration---i.e., the service parameters---of the
@code{guix-service-type} instance, and that of all the
@code{mingetty-service-type} instances in the @var{%base-services} list.
Observe how this is accomplished: first, we arrange for the original
configuration to be bound to the identifier @code{config} in the @var{body},
and then we write the @var{body} so that it evaluates to the desired
configuration.  In particular, notice how we use @code{inherit} to create a
new configuration which has the same values as the old configuration, but
with a few modifications.

@cindex encrypted disk
The configuration for a typical ``desktop'' usage, with an encrypted root
partition, the X11 display server, GNOME and Xfce (users can choose which of
these desktop environments to use at the log-in screen by pressing
@kbd{F1}), network management, power management, and more, would look like
this:

@lisp
@include os-config-desktop.texi
@end lisp

A graphical system with a choice of lightweight window managers instead of
full-blown desktop environments would look like this:

@lisp
@include os-config-lightweight-desktop.texi
@end lisp

This example refers to the @file{/boot/efi} file system by its UUID,
@code{1234-ABCD}.  Replace this UUID with the right UUID on your system, as
returned by the @command{blkid} command.

@xref{Desktop-Dienste}, for the exact list of services provided by
@var{%desktop-services}.  @xref{X.509-Zertifikate}, for background
information about the @code{nss-certs} package that is used here.

Again, @var{%desktop-services} is just a list of service objects.  If you
want to remove services from there, you can do so using the procedures for
list filtering (@pxref{SRFI-1 Filtering and Partitioning,,, guile, GNU Guile
Reference Manual}).  For instance, the following expression returns a list
that contains all the services in @var{%desktop-services} minus the Avahi
service:

@example
(remove (lambda (service)
          (eq? (service-kind service) avahi-service-type))
        %desktop-services)
@end example

@unnumberedsubsubsec Instantiating the System

Assuming the @code{operating-system} declaration is stored in the
@file{my-system-config.scm} file, the @command{guix system reconfigure
my-system-config.scm} command instantiates that configuration, and makes it
the default GRUB boot entry (@pxref{Aufruf von guix system}).

The normal way to change the system configuration is by updating this file
and re-running @command{guix system reconfigure}.  One should never have to
touch files in @file{/etc} or to run commands that modify the system state
such as @command{useradd} or @command{grub-install}.  In fact, you must
avoid that since that would not only void your warranty but also prevent you
from rolling back to previous versions of your system, should you ever need
to.

@cindex roll-back, of the operating system
Speaking of roll-back, each time you run @command{guix system reconfigure},
a new @dfn{generation} of the system is created---without modifying or
deleting previous generations.  Old system generations get an entry in the
bootloader boot menu, allowing you to boot them in case something went wrong
with the latest generation.  Reassuring, no? The @command{guix system
list-generations} command lists the system generations available on disk.
It is also possible to roll back the system via the commands @command{guix
system roll-back} and @command{guix system switch-generation}.

Although the @command{guix system reconfigure} command will not modify
previous generations, you must take care when the current generation is not
the latest (e.g., after invoking @command{guix system roll-back}), since the
operation might overwrite a later generation (@pxref{Aufruf von guix system}).

@unnumberedsubsubsec The Programming Interface

At the Scheme level, the bulk of an @code{operating-system} declaration is
instantiated with the following monadic procedure (@pxref{Die Store-Monade}):

@deffn {Monadic Procedure} operating-system-derivation os
Return a derivation that builds @var{os}, an @code{operating-system} object
(@pxref{Ableitungen}).

The output of the derivation is a single directory that refers to all the
packages, configuration files, and other supporting files needed to
instantiate @var{os}.
@end deffn

This procedure is provided by the @code{(gnu system)} module.  Along with
@code{(gnu services)} (@pxref{Dienste}), this module contains the guts of
GuixSD.  Make sure to visit it!


@node „operating-system“-Referenz
@subsection @code{operating-system} Reference

This section summarizes all the options available in @code{operating-system}
declarations (@pxref{Das Konfigurationssystems nutzen}).

@deftp {Data Type} operating-system
This is the data type representing an operating system configuration.  By
that, we mean all the global system configuration, not per-user
configuration (@pxref{Das Konfigurationssystems nutzen}).

@table @asis
@item @code{kernel} (default: @var{linux-libre})
The package object of the operating system kernel to use@footnote{Currently
only the Linux-libre kernel is supported.  In the future, it will be
possible to use the GNU@tie{}Hurd.}.

@item @code{kernel-arguments} (default: @code{'()})
List of strings or gexps representing additional arguments to pass on the
command-line of the kernel---e.g., @code{("console=ttyS0")}.

@item @code{bootloader}
The system bootloader configuration object.  @xref{Bootloader-Konfiguration}.

@item @code{initrd-modules} (default: @code{%base-initrd-modules})
@cindex initrd
@cindex initial RAM disk
The list of Linux kernel modules that need to be available in the initial
RAM disk.  @xref{Initiale RAM-Disk}.

@item @code{initrd} (default: @code{base-initrd})
A monadic procedure that returns an initial RAM disk for the Linux kernel.
This field is provided to support low-level customization and should rarely
be needed for casual use.  @xref{Initiale RAM-Disk}.

@item @code{firmware} (default: @var{%base-firmware})
@cindex firmware
List of firmware packages loadable by the operating system kernel.

The default includes firmware needed for Atheros- and Broadcom-based WiFi
devices (Linux-libre modules @code{ath9k} and @code{b43-open},
respectively).  @xref{Hardware-Überlegungen}, for more info on supported
hardware.

@item @code{host-name}
The host name.

@item @code{hosts-file}
@cindex hosts file
A file-like object (@pxref{G-Ausdrücke, file-like objects}) for use as
@file{/etc/hosts} (@pxref{Host Names,,, libc, The GNU C Library Reference
Manual}).  The default is a file with entries for @code{localhost} and
@var{host-name}.

@item @code{mapped-devices} (default: @code{'()})
A list of mapped devices.  @xref{Abgebildete Geräte}.

@item @code{file-systems}
A list of file systems.  @xref{Dateisysteme}.

@item @code{swap-devices} (default: @code{'()})
@cindex swap devices
A list of strings identifying devices or files to be used for ``swap space''
(@pxref{Memory Concepts,,, libc, The GNU C Library Reference Manual}).  For
example, @code{'("/dev/sda3")} or @code{'("/swapfile")}.  It is possible to
specify a swap file in a file system on a mapped device, provided that the
necessary device mapping and file system are also specified.  @xref{Abgebildete Geräte} and @ref{Dateisysteme}.

@item @code{users} (default: @code{%base-user-accounts})
@itemx @code{groups} (default: @var{%base-groups})
List of user accounts and groups.  @xref{Benutzerkonten}.

If the @code{users} list lacks a user account with UID@tie{}0, a ``root''
account with UID@tie{}0 is automatically added.

@item @code{skeletons} (default: @code{(default-skeletons)})
A list target file name/file-like object tuples (@pxref{G-Ausdrücke,
file-like objects}).  These are the skeleton files that will be added to the
home directory of newly-created user accounts.

For instance, a valid value may look like this:

@example
`((".bashrc" ,(plain-file "bashrc" "echo Hello\n"))
  (".guile" ,(plain-file "guile"
                         "(use-modules (ice-9 readline))
                          (activate-readline)")))
@end example

@item @code{issue} (default: @var{%default-issue})
A string denoting the contents of the @file{/etc/issue} file, which is
displayed when users log in on a text console.

@item @code{packages} (default: @var{%base-packages})
The set of packages installed in the global profile, which is accessible at
@file{/run/current-system/profile}.

The default set includes core utilities and it is good practice to install
non-core utilities in user profiles (@pxref{Aufruf von guix package}).

@item @code{timezone}
A timezone identifying string---e.g., @code{"Europe/Paris"}.

You can run the @command{tzselect} command to find out which timezone string
corresponds to your region.  Choosing an invalid timezone name causes
@command{guix system} to fail.

@item @code{locale} (default: @code{"en_US.utf8"})
The name of the default locale (@pxref{Locale Names,,, libc, The GNU C
Library Reference Manual}).  @xref{Locales}, for more information.

@item @code{locale-definitions} (default: @var{%default-locale-definitions})
The list of locale definitions to be compiled and that may be used at run
time.  @xref{Locales}.

@item @code{locale-libcs} (default: @code{(list @var{glibc})})
The list of GNU@tie{}libc packages whose locale data and tools are used to
build the locale definitions.  @xref{Locales}, for compatibility
considerations that justify this option.

@item @code{name-service-switch} (default: @var{%default-nss})
Configuration of the libc name service switch (NSS)---a
@code{<name-service-switch>} object.  @xref{Name Service Switch}, for
details.

@item @code{services} (default: @var{%base-services})
A list of service objects denoting system services.  @xref{Dienste}.

@item @code{pam-services} (default: @code{(base-pam-services)})
@cindex PAM
@cindex pluggable authentication modules
@c FIXME: Add xref to PAM services section.
Linux @dfn{pluggable authentication module} (PAM) services.

@item @code{setuid-programs} (default: @var{%setuid-programs})
List of string-valued G-expressions denoting setuid programs.  @xref{Setuid-Programme}.

@item @code{sudoers-file} (default: @var{%sudoers-specification})
@cindex sudoers file
The contents of the @file{/etc/sudoers} file as a file-like object
(@pxref{G-Ausdrücke, @code{local-file} and @code{plain-file}}).

This file specifies which users can use the @command{sudo} command, what
they are allowed to do, and what privileges they may gain.  The default is
that only @code{root} and members of the @code{wheel} group may use
@code{sudo}.

@end table
@end deftp

@node Dateisysteme
@subsection Dateisysteme

The list of file systems to be mounted is specified in the
@code{file-systems} field of the operating system declaration (@pxref{Das Konfigurationssystems nutzen}).  Each file system is declared using the
@code{file-system} form, like this:

@example
(file-system
  (mount-point "/home")
  (device "/dev/sda3")
  (type "ext4"))
@end example

As usual, some of the fields are mandatory---those shown in the example
above---while others can be omitted.  These are described below.

@deftp {Data Type} file-system
Objects of this type represent file systems to be mounted.  They contain the
following members:

@table @asis
@item @code{type}
This is a string specifying the type of the file system---e.g.,
@code{"ext4"}.

@item @code{mount-point}
This designates the place where the file system is to be mounted.

@item @code{device}
This names the ``source'' of the file system.  It can be one of three
things: a file system label, a file system UUID, or the name of a
@file{/dev} node.  Labels and UUIDs offer a way to refer to file systems
without having to hard-code their actual device name@footnote{Note that,
while it is tempting to use @file{/dev/disk/by-uuid} and similar device
names to achieve the same result, this is not recommended: These special
device nodes are created by the udev daemon and may be unavailable at the
time the device is mounted.}.

@findex file-system-label
File system labels are created using the @code{file-system-label} procedure,
UUIDs are created using @code{uuid}, and @file{/dev} node are plain
strings.  Here's an example of a file system referred to by its label, as
shown by the @command{e2label} command:

@example
(file-system
  (mount-point "/home")
  (type "ext4")
  (device (file-system-label "my-home")))
@end example

@findex uuid
UUIDs are converted from their string representation (as shown by the
@command{tune2fs -l} command) using the @code{uuid} form@footnote{The
@code{uuid} form expects 16-byte UUIDs as defined in
@uref{https://tools.ietf.org/html/rfc4122, RFC@tie{}4122}.  This is the form
of UUID used by the ext2 family of file systems and others, but it is
different from ``UUIDs'' found in FAT file systems, for instance.}, like
this:

@example
(file-system
  (mount-point "/home")
  (type "ext4")
  (device (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))
@end example

When the source of a file system is a mapped device (@pxref{Abgebildete Geräte}), its @code{device} field @emph{must} refer to the mapped device
name---e.g., @file{"/dev/mapper/root-partition"}.  This is required so that
the system knows that mounting the file system depends on having the
corresponding device mapping established.

@item @code{flags} (default: @code{'()})
This is a list of symbols denoting mount flags.  Recognized flags include
@code{read-only}, @code{bind-mount}, @code{no-dev} (disallow access to
special files), @code{no-suid} (ignore setuid and setgid bits), and
@code{no-exec} (disallow program execution.)

@item @code{options} (default: @code{#f})
This is either @code{#f}, or a string denoting mount options.

@item @code{mount?} (default: @code{#t})
This value indicates whether to automatically mount the file system when the
system is brought up.  When set to @code{#f}, the file system gets an entry
in @file{/etc/fstab} (read by the @command{mount} command) but is not
automatically mounted.

@item @code{needed-for-boot?} (default: @code{#f})
This Boolean value indicates whether the file system is needed when
booting.  If that is true, then the file system is mounted when the initial
RAM disk (initrd) is loaded.  This is always the case, for instance, for the
root file system.

@item @code{check?} (default: @code{#t})
This Boolean indicates whether the file system needs to be checked for
errors before being mounted.

@item @code{create-mount-point?} (default: @code{#f})
When true, the mount point is created if it does not exist yet.

@item @code{dependencies} (default: @code{'()})
This is a list of @code{<file-system>} or @code{<mapped-device>} objects
representing file systems that must be mounted or mapped devices that must
be opened before (and unmounted or closed after) this one.

As an example, consider a hierarchy of mounts: @file{/sys/fs/cgroup} is a
dependency of @file{/sys/fs/cgroup/cpu} and @file{/sys/fs/cgroup/memory}.

Another example is a file system that depends on a mapped device, for
example for an encrypted partition (@pxref{Abgebildete Geräte}).
@end table
@end deftp

The @code{(gnu system file-systems)} exports the following useful variables.

@defvr {Scheme Variable} %base-file-systems
These are essential file systems that are required on normal systems, such
as @var{%pseudo-terminal-file-system} and @var{%immutable-store} (see
below.)  Operating system declarations should always contain at least these.
@end defvr

@defvr {Scheme Variable} %pseudo-terminal-file-system
This is the file system to be mounted as @file{/dev/pts}.  It supports
@dfn{pseudo-terminals} created @i{via} @code{openpty} and similar functions
(@pxref{Pseudo-Terminals,,, libc, The GNU C Library Reference Manual}).
Pseudo-terminals are used by terminal emulators such as @command{xterm}.
@end defvr

@defvr {Scheme Variable} %shared-memory-file-system
This file system is mounted as @file{/dev/shm} and is used to support memory
sharing across processes (@pxref{Memory-mapped I/O, @code{shm_open},, libc,
The GNU C Library Reference Manual}).
@end defvr

@defvr {Scheme Variable} %immutable-store
This file system performs a read-only ``bind mount'' of @file{/gnu/store},
making it read-only for all the users including @code{root}.  This prevents
against accidental modification by software running as @code{root} or by
system administrators.

The daemon itself is still able to write to the store: it remounts it
read-write in its own ``name space.''
@end defvr

@defvr {Scheme Variable} %binary-format-file-system
The @code{binfmt_misc} file system, which allows handling of arbitrary
executable file types to be delegated to user space.  This requires the
@code{binfmt.ko} kernel module to be loaded.
@end defvr

@defvr {Scheme Variable} %fuse-control-file-system
The @code{fusectl} file system, which allows unprivileged users to mount and
unmount user-space FUSE file systems.  This requires the @code{fuse.ko}
kernel module to be loaded.
@end defvr

@node Abgebildete Geräte
@subsection Abgebildete Geräte

@cindex device mapping
@cindex mapped devices
The Linux kernel has a notion of @dfn{device mapping}: a block device, such
as a hard disk partition, can be @dfn{mapped} into another device, usually
in @code{/dev/mapper/}, with additional processing over the data that flows
through it@footnote{Note that the GNU@tie{}Hurd makes no difference between
the concept of a ``mapped device'' and that of a file system: both boil down
to @emph{translating} input/output operations made on a file to operations
on its backing store.  Thus, the Hurd implements mapped devices, like file
systems, using the generic @dfn{translator} mechanism (@pxref{Translators,,,
hurd, The GNU Hurd Reference Manual}).}.  A typical example is encryption
device mapping: all writes to the mapped device are encrypted, and all reads
are deciphered, transparently.  Guix extends this notion by considering any
device or set of devices that are @dfn{transformed} in some way to create a
new device; for instance, RAID devices are obtained by @dfn{assembling}
several other devices, such as hard disks or partitions, into a new one that
behaves as one partition.  Other examples, not yet implemented, are LVM
logical volumes.

Mapped devices are declared using the @code{mapped-device} form, defined as
follows; for examples, see below.

@deftp {Data Type} mapped-device
Objects of this type represent device mappings that will be made when the
system boots up.

@table @code
@item source
This is either a string specifying the name of the block device to be
mapped, such as @code{"/dev/sda3"}, or a list of such strings when several
devices need to be assembled for creating a new one.

@item target
This string specifies the name of the resulting mapped device.  For kernel
mappers such as encrypted devices of type @code{luks-device-mapping},
specifying @code{"my-partition"} leads to the creation of the
@code{"/dev/mapper/my-partition"} device.  For RAID devices of type
@code{raid-device-mapping}, the full device name such as @code{"/dev/md0"}
needs to be given.

@item type
This must be a @code{mapped-device-kind} object, which specifies how
@var{source} is mapped to @var{target}.
@end table
@end deftp

@defvr {Scheme Variable} luks-device-mapping
This defines LUKS block device encryption using the @command{cryptsetup}
command from the package with the same name.  It relies on the
@code{dm-crypt} Linux kernel module.
@end defvr

@defvr {Scheme Variable} raid-device-mapping
This defines a RAID device, which is assembled using the @code{mdadm}
command from the package with the same name.  It requires a Linux kernel
module for the appropriate RAID level to be loaded, such as @code{raid456}
for RAID-4, RAID-5 or RAID-6, or @code{raid10} for RAID-10.
@end defvr

@cindex disk encryption
@cindex LUKS
The following example specifies a mapping from @file{/dev/sda3} to
@file{/dev/mapper/home} using LUKS---the
@url{https://gitlab.com/cryptsetup/cryptsetup,Linux Unified Key Setup}, a
standard mechanism for disk encryption.  The @file{/dev/mapper/home} device
can then be used as the @code{device} of a @code{file-system} declaration
(@pxref{Dateisysteme}).

@example
(mapped-device
  (source "/dev/sda3")
  (target "home")
  (type luks-device-mapping))
@end example

Alternatively, to become independent of device numbering, one may obtain the
LUKS UUID (@dfn{unique identifier}) of the source device by a command like:

@example
cryptsetup luksUUID /dev/sda3
@end example

and use it as follows:

@example
(mapped-device
  (source (uuid "cb67fc72-0d54-4c88-9d4b-b225f30b0f44"))
  (target "home")
  (type luks-device-mapping))
@end example

@cindex swap encryption
It is also desirable to encrypt swap space, since swap space may contain
sensitive data.  One way to accomplish that is to use a swap file in a file
system on a device mapped via LUKS encryption.  In this way, the swap file
is encrypted because the entire device is encrypted.  @xref{Vor der Installation,,Disk Partitioning}, for an example.

A RAID device formed of the partitions @file{/dev/sda1} and @file{/dev/sdb1}
may be declared as follows:

@example
(mapped-device
  (source (list "/dev/sda1" "/dev/sdb1"))
  (target "/dev/md0")
  (type raid-device-mapping))
@end example

The @file{/dev/md0} device can then be used as the @code{device} of a
@code{file-system} declaration (@pxref{Dateisysteme}).  Note that the RAID
level need not be given; it is chosen during the initial creation and
formatting of the RAID device and is determined automatically later.


@node Benutzerkonten
@subsection Benutzerkonten

@cindex users
@cindex accounts
@cindex user accounts
User accounts and groups are entirely managed through the
@code{operating-system} declaration.  They are specified with the
@code{user-account} and @code{user-group} forms:

@example
(user-account
  (name "alice")
  (group "users")
  (supplementary-groups '("wheel"   ;allow use of sudo, etc.
                          "audio"   ;sound card
                          "video"   ;video devices such as webcams
                          "cdrom")) ;the good ol' CD-ROM
  (comment "Bob's sister")
  (home-directory "/home/alice"))
@end example

When booting or upon completion of @command{guix system reconfigure}, the
system ensures that only the user accounts and groups specified in the
@code{operating-system} declaration exist, and with the specified
properties.  Thus, account or group creations or modifications made by
directly invoking commands such as @command{useradd} are lost upon
reconfiguration or reboot.  This ensures that the system remains exactly as
declared.

@deftp {Data Type} user-account
Objects of this type represent user accounts.  The following members may be
specified:

@table @asis
@item @code{name}
The name of the user account.

@item @code{group}
@cindex groups
This is the name (a string) or identifier (a number) of the user group this
account belongs to.

@item @code{supplementary-groups} (default: @code{'()})
Optionally, this can be defined as a list of group names that this account
belongs to.

@item @code{uid} (default: @code{#f})
This is the user ID for this account (a number), or @code{#f}.  In the
latter case, a number is automatically chosen by the system when the account
is created.

@item @code{comment} (default: @code{""})
A comment about the account, such as the account owner's full name.

@item @code{home-directory}
This is the name of the home directory for the account.

@item @code{create-home-directory?} (default: @code{#t})
Indicates whether the home directory of this account should be created if it
does not exist yet.

@item @code{shell} (default: Bash)
This is a G-expression denoting the file name of a program to be used as the
shell (@pxref{G-Ausdrücke}).

@item @code{system?} (default: @code{#f})
This Boolean value indicates whether the account is a ``system'' account.
System accounts are sometimes treated specially; for instance, graphical
login managers do not list them.

@anchor{user-account-password}
@item @code{password} (default: @code{#f})
You would normally leave this field to @code{#f}, initialize user passwords
as @code{root} with the @command{passwd} command, and then let users change
it with @command{passwd}.  Passwords set with @command{passwd} are of course
preserved across reboot and reconfiguration.

If you @emph{do} want to have a preset password for an account, then this
field must contain the encrypted password, as a string.  @xref{crypt,,,
libc, The GNU C Library Reference Manual}, for more information on password
encryption, and @ref{Encryption,,, guile, GNU Guile Reference Manual}, for
information on Guile's @code{crypt} procedure.

@end table
@end deftp

@cindex groups
User group declarations are even simpler:

@example
(user-group (name "students"))
@end example

@deftp {Data Type} user-group
This type is for, well, user groups.  There are just a few fields:

@table @asis
@item @code{name}
The name of the group.

@item @code{id} (default: @code{#f})
The group identifier (a number).  If @code{#f}, a new number is
automatically allocated when the group is created.

@item @code{system?} (default: @code{#f})
This Boolean value indicates whether the group is a ``system'' group.
System groups have low numerical IDs.

@item @code{password} (default: @code{#f})
What, user groups can have a password? Well, apparently yes.  Unless
@code{#f}, this field specifies the password of the group.

@end table
@end deftp

For convenience, a variable lists all the basic user groups one may expect:

@defvr {Scheme Variable} %base-groups
This is the list of basic user groups that users and/or packages expect to
be present on the system.  This includes groups such as ``root'', ``wheel'',
and ``users'', as well as groups used to control access to specific devices
such as ``audio'', ``disk'', and ``cdrom''.
@end defvr

@defvr {Scheme Variable} %base-user-accounts
This is the list of basic system accounts that programs may expect to find
on a GNU/Linux system, such as the ``nobody'' account.

Note that the ``root'' account is not included here.  It is a special-case
and is automatically added whether or not it is specified.
@end defvr

@node Locales
@subsection Locales

@cindex locale
A @dfn{locale} defines cultural conventions for a particular language and
region of the world (@pxref{Locales,,, libc, The GNU C Library Reference
Manual}).  Each locale has a name that typically has the form
@code{@var{language}_@var{territory}.@var{codeset}}---e.g.,
@code{fr_LU.utf8} designates the locale for the French language, with
cultural conventions from Luxembourg, and using the UTF-8 encoding.

@cindex locale definition
Usually, you will want to specify the default locale for the machine using
the @code{locale} field of the @code{operating-system} declaration
(@pxref{„operating-system“-Referenz, @code{locale}}).

The selected locale is automatically added to the @dfn{locale definitions}
known to the system if needed, with its codeset inferred from its
name---e.g., @code{bo_CN.utf8} will be assumed to use the @code{UTF-8}
codeset.  Additional locale definitions can be specified in the
@code{locale-definitions} slot of @code{operating-system}---this is useful,
for instance, if the codeset could not be inferred from the locale name.
The default set of locale definitions includes some widely used locales, but
not all the available locales, in order to save space.

For instance, to add the North Frisian locale for Germany, the value of that
field may be:

@example
(cons (locale-definition
        (name "fy_DE.utf8") (source "fy_DE"))
      %default-locale-definitions)
@end example

Likewise, to save space, one might want @code{locale-definitions} to list
only the locales that are actually used, as in:

@example
(list (locale-definition
        (name "ja_JP.eucjp") (source "ja_JP")
        (charset "EUC-JP")))
@end example

@vindex LOCPATH
The compiled locale definitions are available at
@file{/run/current-system/locale/X.Y}, where @code{X.Y} is the libc version,
which is the default location where the GNU@tie{}libc provided by Guix looks
for locale data.  This can be overridden using the @code{LOCPATH}
environment variable (@pxref{locales-and-locpath, @code{LOCPATH} and locale
packages}).

The @code{locale-definition} form is provided by the @code{(gnu system
locale)} module.  Details are given below.

@deftp {Data Type} locale-definition
This is the data type of a locale definition.

@table @asis

@item @code{name}
The name of the locale.  @xref{Locale Names,,, libc, The GNU C Library
Reference Manual}, for more information on locale names.

@item @code{source}
The name of the source for that locale.  This is typically the
@code{@var{language}_@var{territory}} part of the locale name.

@item @code{charset} (default: @code{"UTF-8"})
The ``character set'' or ``code set'' for that locale,
@uref{http://www.iana.org/assignments/character-sets, as defined by IANA}.

@end table
@end deftp

@defvr {Scheme Variable} %default-locale-definitions
A list of commonly used UTF-8 locales, used as the default value of the
@code{locale-definitions} field of @code{operating-system} declarations.

@cindex locale name
@cindex normalized codeset in locale names
These locale definitions use the @dfn{normalized codeset} for the part that
follows the dot in the name (@pxref{Using gettextized software, normalized
codeset,, libc, The GNU C Library Reference Manual}).  So for instance it
has @code{uk_UA.utf8} but @emph{not}, say, @code{uk_UA.UTF-8}.
@end defvr

@subsubsection Locale Data Compatibility Considerations

@cindex incompatibility, of locale data
@code{operating-system} declarations provide a @code{locale-libcs} field to
specify the GNU@tie{}libc packages that are used to compile locale
declarations (@pxref{„operating-system“-Referenz}).  ``Why would I care?'',
you may ask.  Well, it turns out that the binary format of locale data is
occasionally incompatible from one libc version to another.

@c See <https://sourceware.org/ml/libc-alpha/2015-09/msg00575.html>
@c and <https://lists.gnu.org/archive/html/guix-devel/2015-08/msg00737.html>.
For instance, a program linked against libc version 2.21 is unable to read
locale data produced with libc 2.22; worse, that program @emph{aborts}
instead of simply ignoring the incompatible locale data@footnote{Versions
2.23 and later of GNU@tie{}libc will simply skip the incompatible locale
data, which is already an improvement.}.  Similarly, a program linked
against libc 2.22 can read most, but not all, of the locale data from libc
2.21 (specifically, @code{LC_COLLATE} data is incompatible); thus calls to
@code{setlocale} may fail, but programs will not abort.

The ``problem'' in GuixSD is that users have a lot of freedom: They can
choose whether and when to upgrade software in their profiles, and might be
using a libc version different from the one the system administrator used to
build the system-wide locale data.

Fortunately, unprivileged users can also install their own locale data and
define @var{GUIX_LOCPATH} accordingly (@pxref{locales-and-locpath,
@code{GUIX_LOCPATH} and locale packages}).

Still, it is best if the system-wide locale data at
@file{/run/current-system/locale} is built for all the libc versions
actually in use on the system, so that all the programs can access it---this
is especially crucial on a multi-user system.  To do that, the administrator
can specify several libc packages in the @code{locale-libcs} field of
@code{operating-system}:

@example
(use-package-modules base)

(operating-system
  ;; @dots{}
  (locale-libcs (list glibc-2.21 (canonical-package glibc))))
@end example

This example would lead to a system containing locale definitions for both
libc 2.21 and the current version of libc in
@file{/run/current-system/locale}.


@node Dienste
@subsection Dienste

@cindex system services
An important part of preparing an @code{operating-system} declaration is
listing @dfn{system services} and their configuration (@pxref{Das Konfigurationssystems nutzen}).  System services are typically daemons launched when
the system boots, or other actions needed at that time---e.g., configuring
network access.

GuixSD has a broad definition of ``service'' (@pxref{Dienstkompositionen}),
but many services are managed by the GNU@tie{}Shepherd (@pxref{Shepherd-Dienste}).  On a running system, the @command{herd} command allows you to
list the available services, show their status, start and stop them, or do
other specific operations (@pxref{Jump Start,,, shepherd, The GNU Shepherd
Manual}).  For example:

@example
# herd status
@end example

The above command, run as @code{root}, lists the currently defined
services.  The @command{herd doc} command shows a synopsis of the given
service:

@example
# herd doc nscd
Run libc's name service cache daemon (nscd).
@end example

The @command{start}, @command{stop}, and @command{restart} sub-commands have
the effect you would expect.  For instance, the commands below stop the nscd
service and restart the Xorg display server:

@example
# herd stop nscd
Service nscd has been stopped.
# herd restart xorg-server
Service xorg-server has been stopped.
Service xorg-server has been started.
@end example

The following sections document the available services, starting with the
core services, that may be used in an @code{operating-system} declaration.

@menu
* Basisdienste::             Essenzielle Systemdienste
* Geplante Auftragsausführung::  Der mcron-Dienst.
* Log-Rotation::             Der rottlog-Dienst.
* Netzwerkdienste::          Netzwerkeinrichtung, SSH-Daemon etc.
* X Window::                 Graphische Anzeige.
* Druckdienste::             Unterstützung für lokale und entfernte 
                               Drucker.
* Desktop-Dienste::          D-Bus- und Desktop-Dienste.
* Tondienste::               Dienste für ALSA und Pulseaudio.
* Datenbankdienste::         SQL-Datenbanken, Schlüssel-Wert-Speicher etc.
* Mail-Dienste::             IMAP, POP3, SMTP und so weiter.
* Kurznachrichtendienste::   Dienste für Kurznachrichten.
* Telefondienste::           Telefoniedienste.
* Überwachungsdienste::     Dienste zur Systemüberwachung.
* Kerberos-Dienste::         Kerberos-Dienste.
* Web-Dienste::              Web-Server.
* Zertifikatsdienste::       TLS-Zertifikate via Let’s Encrypt.
* DNS-Dienste::              DNS-Daemons.
* VPN-Dienste::              VPN-Daemons.
* Network File System::      Dienste mit Bezug zum Netzwerkdateisystem.
* Kontinuierliche Integration::  Der Cuirass-Dienst
* Power Management Services::  Extending battery life.
* Audio-Dienste::            Der MPD.
* Virtualisierungsdienste::  Dienste für virtuelle Maschinen.
* Versionskontrolldienste::  Entfernten Zugang zu Git-Repositorys bieten.
* Spieldienste::             Spielserver.
* Verschiedene Dienste::     Andere Dienste.
@end menu

@node Basisdienste
@subsubsection Basisdienste

The @code{(gnu services base)} module provides definitions for the basic
services that one expects from the system.  The services exported by this
module are listed below.

@defvr {Scheme Variable} %base-services
This variable contains a list of basic services (@pxref{Diensttypen und Dienste}, for more information on service objects) one would expect from
the system: a login service (mingetty) on each tty, syslogd, the libc name
service cache daemon (nscd), the udev device manager, and more.

This is the default value of the @code{services} field of
@code{operating-system} declarations.  Usually, when customizing a system,
you will want to append services to @var{%base-services}, like this:

@example
(cons* (avahi-service) (lsh-service) %base-services)
@end example
@end defvr

@defvr {Scheme Variable} special-files-service-type
This is the service that sets up ``special files'' such as @file{/bin/sh};
an instance of it is part of @code{%base-services}.

The value associated with @code{special-files-service-type} services must be
a list of tuples where the first element is the ``special file'' and the
second element is its target.  By default it is:

@cindex @file{/bin/sh}
@cindex @file{sh}, in @file{/bin}
@example
`(("/bin/sh" ,(file-append @var{bash} "/bin/sh")))
@end example

@cindex @file{/usr/bin/env}
@cindex @file{env}, in @file{/usr/bin}
If you want to add, say, @code{/usr/bin/env} to your system, you can change
it to:

@example
`(("/bin/sh" ,(file-append @var{bash} "/bin/sh"))
  ("/usr/bin/env" ,(file-append @var{coreutils} "/bin/env")))
@end example

Since this is part of @code{%base-services}, you can use
@code{modify-services} to customize the set of special files (@pxref{Service-Referenz, @code{modify-services}}).  But the simple way to add a special
file is @i{via} the @code{extra-special-file} procedure (see below.)
@end defvr

@deffn {Scheme Procedure} extra-special-file @var{file} @var{target}
Use @var{target} as the ``special file'' @var{file}.

For example, adding the following lines to the @code{services} field of your
operating system declaration leads to a @file{/usr/bin/env} symlink:

@example
(extra-special-file "/usr/bin/env"
                    (file-append coreutils "/bin/env"))
@end example
@end deffn

@deffn {Scheme Procedure} host-name-service @var{name}
Return a service that sets the host name to @var{name}.
@end deffn

@deffn {Scheme Procedure} login-service @var{config}
Return a service to run login according to @var{config}, a
@code{<login-configuration>} object, which specifies the message of the day,
among other things.
@end deffn

@deftp {Data Type} login-configuration
This is the data type representing the configuration of login.

@table @asis

@item @code{motd}
@cindex message of the day
A file-like object containing the ``message of the day''.

@item @code{allow-empty-passwords?} (default: @code{#t})
Allow empty passwords by default so that first-time users can log in when
the 'root' account has just been created.

@end table
@end deftp

@deffn {Scheme Procedure} mingetty-service @var{config}
Return a service to run mingetty according to @var{config}, a
@code{<mingetty-configuration>} object, which specifies the tty to run,
among other things.
@end deffn

@deftp {Data Type} mingetty-configuration
This is the data type representing the configuration of Mingetty, which
provides the default implementation of virtual console log-in.

@table @asis

@item @code{tty}
The name of the console this Mingetty runs on---e.g., @code{"tty1"}.

@item @code{auto-login} (default: @code{#f})
When true, this field must be a string denoting the user name under which
the system automatically logs in.  When it is @code{#f}, a user name and
password must be entered to log in.

@item @code{login-program} (default: @code{#f})
This must be either @code{#f}, in which case the default log-in program is
used (@command{login} from the Shadow tool suite), or a gexp denoting the
name of the log-in program.

@item @code{login-pause?} (default: @code{#f})
When set to @code{#t} in conjunction with @var{auto-login}, the user will
have to press a key before the log-in shell is launched.

@item @code{mingetty} (default: @var{mingetty})
The Mingetty package to use.

@end table
@end deftp

@deffn {Scheme Procedure} agetty-service @var{config}
Return a service to run agetty according to @var{config}, an
@code{<agetty-configuration>} object, which specifies the tty to run, among
other things.
@end deffn

@deftp {Data Type} agetty-configuration
This is the data type representing the configuration of agetty, which
implements virtual and serial console log-in.  See the @code{agetty(8)} man
page for more information.

@table @asis

@item @code{tty}
The name of the console this agetty runs on, as a string---e.g.,
@code{"ttyS0"}. This argument is optional, it will default to a reasonable
default serial port used by the kernel Linux.

For this, if there is a value for an option @code{agetty.tty} in the kernel
command line, agetty will extract the device name of the serial port from it
and use that.

If not and if there is a value for an option @code{console} with a tty in
the Linux command line, agetty will extract the device name of the serial
port from it and use that.

In both cases, agetty will leave the other serial device settings (baud rate
etc.) alone---in the hope that Linux pinned them to the correct values.

@item @code{baud-rate} (default: @code{#f})
A string containing a comma-separated list of one or more baud rates, in
descending order.

@item @code{term} (default: @code{#f})
A string containing the value used for the @code{TERM} environment variable.

@item @code{eight-bits?} (default: @code{#f})
When @code{#t}, the tty is assumed to be 8-bit clean, and parity detection
is disabled.

@item @code{auto-login} (default: @code{#f})
When passed a login name, as a string, the specified user will be logged in
automatically without prompting for their login name or password.

@item @code{no-reset?} (default: @code{#f})
When @code{#t}, don't reset terminal cflags (control modes).

@item @code{host} (default: @code{#f})
This accepts a string containing the "login_host", which will be written
into the @file{/var/run/utmpx} file.

@item @code{remote?} (default: @code{#f})
When set to @code{#t} in conjunction with @var{host}, this will add an
@code{-r} fakehost option to the command line of the login program specified
in @var{login-program}.

@item @code{flow-control?} (default: @code{#f})
When set to @code{#t}, enable hardware (RTS/CTS) flow control.

@item @code{no-issue?} (default: @code{#f})
When set to @code{#t}, the contents of the @file{/etc/issue} file will not
be displayed before presenting the login prompt.

@item @code{init-string} (default: @code{#f})
This accepts a string that will be sent to the tty or modem before sending
anything else.  It can be used to initialize a modem.

@item @code{no-clear?} (default: @code{#f})
When set to @code{#t}, agetty will not clear the screen before showing the
login prompt.

@item @code{login-program} (default: (file-append shadow "/bin/login"))
This must be either a gexp denoting the name of a log-in program, or unset,
in which case the default value is the @command{login} from the Shadow tool
suite.

@item @code{local-line} (default: @code{#f})
Control the CLOCAL line flag.  This accepts one of three symbols as
arguments, @code{'auto}, @code{'always}, or @code{'never}. If @code{#f}, the
default value chosen by agetty is @code{'auto}.

@item @code{extract-baud?} (default: @code{#f})
When set to @code{#t}, instruct agetty to try to extract the baud rate from
the status messages produced by certain types of modems.

@item @code{skip-login?} (default: @code{#f})
When set to @code{#t}, do not prompt the user for a login name.  This can be
used with @var{login-program} field to use non-standard login systems.

@item @code{no-newline?} (default: @code{#f})
When set to @code{#t}, do not print a newline before printing the
@file{/etc/issue} file.

@c Is this dangerous only when used with login-program, or always?
@item @code{login-options} (default: @code{#f})
This option accepts a string containing options that are passed to the login
program.  When used with the @var{login-program}, be aware that a malicious
user could try to enter a login name containing embedded options that could
be parsed by the login program.

@item @code{login-pause} (default: @code{#f})
When set to @code{#t}, wait for any key before showing the login prompt.
This can be used in conjunction with @var{auto-login} to save memory by
lazily spawning shells.

@item @code{chroot} (default: @code{#f})
Change root to the specified directory.  This option accepts a directory
path as a string.

@item @code{hangup?} (default: @code{#f})
Use the Linux system call @code{vhangup} to do a virtual hangup of the
specified terminal.

@item @code{keep-baud?} (default: @code{#f})
When set to @code{#t}, try to keep the existing baud rate.  The baud rates
from @var{baud-rate} are used when agetty receives a @key{BREAK} character.

@item @code{timeout} (default: @code{#f})
When set to an integer value, terminate if no user name could be read within
@var{timeout} seconds.

@item @code{detect-case?} (default: @code{#f})
When set to @code{#t}, turn on support for detecting an uppercase-only
terminal.  This setting will detect a login name containing only uppercase
letters as indicating an uppercase-only terminal and turn on some
upper-to-lower case conversions.  Note that this will not support Unicode
characters.

@item @code{wait-cr?} (default: @code{#f})
When set to @code{#t}, wait for the user or modem to send a carriage-return
or linefeed character before displaying @file{/etc/issue} or login prompt.
This is typically used with the @var{init-string} option.

@item @code{no-hints?} (default: @code{#f})
When set to @code{#t}, do not print hints about Num, Caps, and Scroll locks.

@item @code{no-hostname?} (default: @code{#f})
By default, the hostname is printed.  When this option is set to @code{#t},
no hostname will be shown at all.

@item @code{long-hostname?} (default: @code{#f})
By default, the hostname is only printed until the first dot.  When this
option is set to @code{#t}, the fully qualified hostname by
@code{gethostname} or @code{getaddrinfo} is shown.

@item @code{erase-characters} (default: @code{#f})
This option accepts a string of additional characters that should be
interpreted as backspace when the user types their login name.

@item @code{kill-characters} (default: @code{#f})
This option accepts a string that should be interpreted to mean "ignore all
previous characters" (also called a "kill" character) when the types their
login name.

@item @code{chdir} (default: @code{#f})
This option accepts, as a string, a directory path that will be changed to
before login.

@item @code{delay} (default: @code{#f})
This options accepts, as an integer, the number of seconds to sleep before
opening the tty and displaying the login prompt.

@item @code{nice} (default: @code{#f})
This option accepts, as an integer, the nice value with which to run the
@command{login} program.

@item @code{extra-options} (default: @code{'()})
This option provides an "escape hatch" for the user to provide arbitrary
command-line arguments to @command{agetty} as a list of strings.

@end table
@end deftp

@deffn {Scheme Procedure} kmscon-service-type @var{config}
Return a service to run
@uref{https://www.freedesktop.org/wiki/Software/kmscon,kmscon} according to
@var{config}, a @code{<kmscon-configuration>} object, which specifies the
tty to run, among other things.
@end deffn

@deftp {Data Type} kmscon-configuration
This is the data type representing the configuration of Kmscon, which
implements virtual console log-in.

@table @asis

@item @code{virtual-terminal}
The name of the console this Kmscon runs on---e.g., @code{"tty1"}.

@item @code{login-program} (default: @code{#~(string-append #$shadow "/bin/login")})
A gexp denoting the name of the log-in program. The default log-in program
is @command{login} from the Shadow tool suite.

@item @code{login-arguments} (default: @code{'("-p")})
A list of arguments to pass to @command{login}.

@item @code{hardware-acceleration?} (default: #f)
Whether to use hardware acceleration.

@item @code{kmscon} (default: @var{kmscon})
The Kmscon package to use.

@end table
@end deftp

@cindex name service cache daemon
@cindex nscd
@deffn {Scheme Procedure} nscd-service [@var{config}] [#:glibc glibc] @
                [#:name-services '()] Return a service that runs the libc name service cache
daemon (nscd) with the given @var{config}---an @code{<nscd-configuration>}
object.  @xref{Name Service Switch}, for an example.
@end deffn

@defvr {Scheme Variable} %nscd-default-configuration
This is the default @code{<nscd-configuration>} value (see below) used by
@code{nscd-service}.  It uses the caches defined by
@var{%nscd-default-caches}; see below.
@end defvr

@deftp {Data Type} nscd-configuration
This is the data type representing the name service cache daemon (nscd)
configuration.

@table @asis

@item @code{name-services} (default: @code{'()})
List of packages denoting @dfn{name services} that must be visible to the
nscd---e.g., @code{(list @var{nss-mdns})}.

@item @code{glibc} (default: @var{glibc})
Package object denoting the GNU C Library providing the @command{nscd}
command.

@item @code{log-file} (default: @code{"/var/log/nscd.log"})
Name of the nscd log file.  This is where debugging output goes when
@code{debug-level} is strictly positive.

@item @code{debug-level} (default: @code{0})
Integer denoting the debugging levels.  Higher numbers mean that more
debugging output is logged.

@item @code{caches} (default: @var{%nscd-default-caches})
List of @code{<nscd-cache>} objects denoting things to be cached; see below.

@end table
@end deftp

@deftp {Data Type} nscd-cache
Data type representing a cache database of nscd and its parameters.

@table @asis

@item @code{database}
This is a symbol representing the name of the database to be cached.  Valid
values are @code{passwd}, @code{group}, @code{hosts}, and @code{services},
which designate the corresponding NSS database (@pxref{NSS Basics,,, libc,
The GNU C Library Reference Manual}).

@item @code{positive-time-to-live}
@itemx @code{negative-time-to-live} (default: @code{20})
A number representing the number of seconds during which a positive or
negative lookup result remains in cache.

@item @code{check-files?} (default: @code{#t})
Whether to check for updates of the files corresponding to @var{database}.

For instance, when @var{database} is @code{hosts}, setting this flag
instructs nscd to check for updates in @file{/etc/hosts} and to take them
into account.

@item @code{persistent?} (default: @code{#t})
Whether the cache should be stored persistently on disk.

@item @code{shared?} (default: @code{#t})
Whether the cache should be shared among users.

@item @code{max-database-size} (default: 32@tie{}MiB)
Maximum size in bytes of the database cache.

@c XXX: 'suggested-size' and 'auto-propagate?' seem to be expert
@c settings, so leave them out.

@end table
@end deftp

@defvr {Scheme Variable} %nscd-default-caches
List of @code{<nscd-cache>} objects used by default by
@code{nscd-configuration} (see above).

It enables persistent and aggressive caching of service and host name
lookups.  The latter provides better host name lookup performance,
resilience in the face of unreliable name servers, and also better
privacy---often the result of host name lookups is in local cache, so
external name servers do not even need to be queried.
@end defvr

@anchor{syslog-configuration-type}
@cindex syslog
@cindex logging
@deftp {Data Type} syslog-configuration
This data type represents the configuration of the syslog daemon.

@table @asis
@item @code{syslogd} (default: @code{#~(string-append #$inetutils "/libexec/syslogd")})
The syslog daemon to use.

@item @code{config-file} (default: @code{%default-syslog.conf})
The syslog configuration file to use.

@end table
@end deftp

@anchor{syslog-service}
@cindex syslog
@deffn {Scheme Procedure} syslog-service @var{config}
Return a service that runs a syslog daemon according to @var{config}.

@xref{syslogd invocation,,, inetutils, GNU Inetutils}, for more information
on the configuration file syntax.
@end deffn

@defvr {Scheme Variable} guix-service-type
This is the type of the service that runs the build daemon,
@command{guix-daemon} (@pxref{Aufruf des guix-daemon}).  Its value must be a
@code{guix-configuration} record as described below.
@end defvr

@anchor{guix-configuration-type}
@deftp {Data Type} guix-configuration
This data type represents the configuration of the Guix build daemon.
@xref{Aufruf des guix-daemon}, for more information.

@table @asis
@item @code{guix} (default: @var{guix})
The Guix package to use.

@item @code{build-group} (default: @code{"guixbuild"})
Name of the group for build user accounts.

@item @code{build-accounts} (default: @code{10})
Number of build user accounts to create.

@item @code{authorize-key?} (default: @code{#t})
@cindex Substitute, deren Autorisierung
Whether to authorize the substitute keys listed in
@code{authorized-keys}---by default that of @code{hydra.gnu.org}
(@pxref{Substitute}).

@vindex %default-authorized-guix-keys
@item @code{authorized-keys} (default: @var{%default-authorized-guix-keys})
The list of authorized key files for archive imports, as a list of
string-valued gexps (@pxref{Aufruf von guix archive}).  By default, it
contains that of @code{hydra.gnu.org} (@pxref{Substitute}).

@item @code{use-substitutes?} (default: @code{#t})
Whether to use substitutes.

@item @code{substitute-urls} (default: @var{%default-substitute-urls})
The list of URLs where to look for substitutes by default.

@item @code{max-silent-time} (default: @code{0})
@itemx @code{timeout} (default: @code{0})
The number of seconds of silence and the number of seconds of activity,
respectively, after which a build process times out.  A value of zero
disables the timeout.

@item @code{log-compression} (default: @code{'bzip2})
The type of compression used for build logs---one of @code{gzip},
@code{bzip2}, or @code{none}.

@item @code{extra-options} (default: @code{'()})
List of extra command-line options for @command{guix-daemon}.

@item @code{log-file} (default: @code{"/var/log/guix-daemon.log"})
File where @command{guix-daemon}'s standard output and standard error are
written.

@item @code{http-proxy} (default: @code{#f})
The HTTP proxy used for downloading fixed-output derivations and
substitutes.

@item @code{tmpdir} (default: @code{#f})
A directory path where the @command{guix-daemon} will perform builds.

@end table
@end deftp

@deffn {Scheme Procedure} udev-service [#:udev @var{eudev} #:rules @code{'()}]
Run @var{udev}, which populates the @file{/dev} directory dynamically.  udev
rules can be provided as a list of files through the @var{rules} variable.
The procedures @var{udev-rule} and @var{file->udev-rule} from @code{(gnu
services base)} simplify the creation of such rule files.

@deffn {Scheme Procedure} udev-rule [@var{file-name} @var{contents}]
Return a udev-rule file named @var{file-name} containing the rules defined
by the @var{contents} literal.

In the following example, a rule for a USB device is defined to be stored in
the file @file{90-usb-thing.rules}.  The rule runs a script upon detecting a
USB device with a given product identifier.

@example
(define %example-udev-rule
  (udev-rule
    "90-usb-thing.rules"
    (string-append "ACTION==\"add\", SUBSYSTEM==\"usb\", "
                   "ATTR@{product@}==\"Example\", "
                   "RUN+=\"/path/to/script\"")))
@end example
@end deffn

Here we show how the default @var{udev-service} can be extended with it.

@example
(operating-system
 ;; @dots{}
 (services
 (modify-services %desktop-services
   (udev-service-type config =>
     (udev-configuration (inherit config)
      (rules (append (udev-configuration-rules config)
                     (list %example-udev-rule))))))))
@end example

@deffn {Scheme Procedure} file->udev-rule [@var{file-name} @var{file}]
Return a udev file named @var{file-name} containing the rules defined within
@var{file}, a file-like object.

The following example showcases how we can use an existing rule file.

@example
(use-modules (guix download)     ;for url-fetch
             (guix packages)     ;for origin
             ;; @dots{})

(define %android-udev-rules
  (file->udev-rule
    "51-android-udev.rules"
    (let ((version "20170910"))
      (origin
       (method url-fetch)
       (uri (string-append "https://raw.githubusercontent.com/M0Rf30/"
                           "android-udev-rules/" version "/51-android.rules"))
       (sha256
        (base32 "0lmmagpyb6xsq6zcr2w1cyx9qmjqmajkvrdbhjx32gqf1d9is003"))))))
@end example
@end deffn

Additionally, Guix package definitions can be included in @var{rules} in
order to extend the udev rules with the definitions found under their
@file{lib/udev/rules.d} sub-directory.  In lieu of the previous
@var{file->udev-rule} example, we could have used the
@var{android-udev-rules} package which exists in Guix in the @code{(gnu
packages android)} module.

The following example shows how to use the @var{android-udev-rules} package
so that the Android tool @command{adb} can detect devices without root
privileges.  It also details how to create the @code{adbusers} group, which
is required for the proper functioning of the rules defined within the
@var{android-udev-rules} package.  To create such a group, we must define it
both as part of the @var{supplementary-groups} of our @var{user-account}
declaration, as well as in the @var{groups} field of the
@var{operating-system} record.

@example
(use-modules (gnu packages android)  ;for android-udev-rules
             (gnu system shadow)     ;for user-group
             ;; @dots{})

(operating-system
  ;; @dots{}
  (users (cons (user-acount
                ;; @dots{}
                (supplementary-groups
                 '("adbusers"   ;for adb
                   "wheel" "netdev" "audio" "video"))
                ;; @dots{})))

  (groups (cons (user-group (system? #t) (name "adbusers"))
                %base-groups))

  ;; @dots{}

  (services
    (modify-services %desktop-services
      (udev-service-type config =>
       (udev-configuration (inherit config)
       (rules (cons* android-udev-rules
              (udev-configuration-rules config))))))))
@end example
@end deffn

@defvr {Scheme Variable} urandom-seed-service-type
Save some entropy in @var{%random-seed-file} to seed @file{/dev/urandom}
when rebooting.  It also tries to seed @file{/dev/urandom} from
@file{/dev/hwrng} while booting, if @file{/dev/hwrng} exists and is
readable.
@end defvr

@defvr {Scheme Variable} %random-seed-file
This is the name of the file where some random bytes are saved by
@var{urandom-seed-service} to seed @file{/dev/urandom} when rebooting.  It
defaults to @file{/var/lib/random-seed}.
@end defvr

@cindex keymap
@cindex keyboard
@deffn {Scheme Procedure} console-keymap-service @var{files} ...
@cindex keyboard layout
Return a service to load console keymaps from @var{files} using
@command{loadkeys} command.  Most likely, you want to load some default
keymap, which can be done like this:

@example
(console-keymap-service "dvorak")
@end example

Or, for example, for a Swedish keyboard, you may need to combine the
following keymaps:
@example
(console-keymap-service "se-lat6" "se-fi-lat6")
@end example

Also you can specify a full file name (or file names) of your keymap(s).
See @code{man loadkeys} for details.

@end deffn

@cindex mouse
@cindex gpm
@defvr {Scheme Variable} gpm-service-type
This is the type of the service that runs GPM, the @dfn{general-purpose
mouse daemon}, which provides mouse support to the Linux console.  GPM
allows users to use the mouse in the console, notably to select, copy, and
paste text.

The value for services of this type must be a @code{gpm-configuration} (see
below).  This service is not part of @var{%base-services}.
@end defvr

@deftp {Data Type} gpm-configuration
Data type representing the configuration of GPM.

@table @asis
@item @code{options} (default: @code{%default-gpm-options})
Command-line options passed to @command{gpm}.  The default set of options
instruct @command{gpm} to listen to mouse events on @file{/dev/input/mice}.
@xref{Command Line,,, gpm, gpm manual}, for more information.

@item @code{gpm} (default: @code{gpm})
The GPM package to use.

@end table
@end deftp

@anchor{guix-publish-service-type}
@deffn {Scheme Variable} guix-publish-service-type
This is the service type for @command{guix publish} (@pxref{Aufruf von guix publish}).  Its value must be a @code{guix-configuration} object, as
described below.

This assumes that @file{/etc/guix} already contains a signing key pair as
created by @command{guix archive --generate-key} (@pxref{Aufruf von guix archive}).  If that is not the case, the service will fail to start.
@end deffn

@deftp {Data Type} guix-publish-configuration
Data type representing the configuration of the @code{guix publish} service.

@table @asis
@item @code{guix} (default: @code{guix})
The Guix package to use.

@item @code{port} (default: @code{80})
The TCP port to listen for connections.

@item @code{host} (default: @code{"localhost"})
The host (and thus, network interface) to listen to.  Use @code{"0.0.0.0"}
to listen on all the network interfaces.

@item @code{compression-level} (Vorgabe: @code{3})
The gzip compression level at which substitutes are compressed.  Use
@code{0} to disable compression altogether, and @code{9} to get the best
compression ratio at the expense of increased CPU usage.

@item @code{nar-path} (default: @code{"nar"})
The URL path at which ``nars'' can be fetched.  @xref{Aufruf von guix publish,
@code{--nar-path}}, for details.

@item @code{cache} (default: @code{#f})
When it is @code{#f}, disable caching and instead generate archives on
demand.  Otherwise, this should be the name of a directory---e.g.,
@code{"/var/cache/guix/publish"}---where @command{guix publish} caches
archives and meta-data ready to be sent.  @xref{Aufruf von guix publish,
@option{--cache}}, for more information on the tradeoffs involved.

@item @code{workers} (default: @code{#f})
When it is an integer, this is the number of worker threads used for
caching; when @code{#f}, the number of processors is used.  @xref{Aufruf von guix publish, @option{--workers}}, for more information.

@item @code{ttl} (default: @code{#f})
When it is an integer, this denotes the @dfn{time-to-live} in seconds of the
published archives.  @xref{Aufruf von guix publish, @option{--ttl}}, for more
information.
@end table
@end deftp

@anchor{rngd-service}
@deffn {Scheme Procedure} rngd-service [#:rng-tools @var{rng-tools}] @
            [#:device "/dev/hwrng"] Return a service that runs the @command{rngd}
program from @var{rng-tools} to add @var{device} to the kernel's entropy
pool.  The service will fail if @var{device} does not exist.
@end deffn

@anchor{pam-limits-service}
@cindex session limits
@cindex ulimit
@cindex priority
@cindex realtime
@cindex jackd
@deffn {Scheme Procedure} pam-limits-service [#:limits @code{'()}]

Return a service that installs a configuration file for the
@uref{http://linux-pam.org/Linux-PAM-html/sag-pam_limits.html,
@code{pam_limits} module}.  The procedure optionally takes a list of
@code{pam-limits-entry} values, which can be used to specify @code{ulimit}
limits and nice priority limits to user sessions.

The following limits definition sets two hard and soft limits for all login
sessions of users in the @code{realtime} group:

@example
(pam-limits-service
 (list
  (pam-limits-entry "@@realtime" 'both 'rtprio 99)
  (pam-limits-entry "@@realtime" 'both 'memlock 'unlimited)))
@end example

The first entry increases the maximum realtime priority for non-privileged
processes; the second entry lifts any restriction of the maximum address
space that can be locked in memory.  These settings are commonly used for
real-time audio systems.
@end deffn

@node Geplante Auftragsausführung
@subsubsection Geplante Auftragsausführung

@cindex cron
@cindex mcron
@cindex scheduling jobs
The @code{(gnu services mcron)} module provides an interface to
GNU@tie{}mcron, a daemon to run jobs at scheduled times (@pxref{Top,,,
mcron, GNU@tie{}mcron}).  GNU@tie{}mcron is similar to the traditional Unix
@command{cron} daemon; the main difference is that it is implemented in
Guile Scheme, which provides a lot of flexibility when specifying the
scheduling of jobs and their actions.

The example below defines an operating system that runs the
@command{updatedb} (@pxref{Invoking updatedb,,, find, Finding Files})  and
the @command{guix gc} commands (@pxref{Aufruf von guix gc}) daily, as well as
the @command{mkid} command on behalf of an unprivileged user (@pxref{mkid
invocation,,, idutils, ID Database Utilities}).  It uses gexps to introduce
job definitions that are passed to mcron (@pxref{G-Ausdrücke}).

@lisp
(use-modules (guix) (gnu) (gnu services mcron))
(use-package-modules base idutils)

(define updatedb-job
  ;; Run 'updatedb' at 3AM every day.  Here we write the
  ;; job's action as a Scheme procedure.
  #~(job '(next-hour '(3))
         (lambda ()
           (execl (string-append #$findutils "/bin/updatedb")
                  "updatedb"
                  "--prunepaths=/tmp /var/tmp /gnu/store"))))

(define garbage-collector-job
  ;; Collect garbage 5 minutes after midnight every day.
  ;; The job's action is a shell command.
  #~(job "5 0 * * *"            ;Vixie cron syntax
         "guix gc -F 1G"))

(define idutils-job
  ;; Update the index database as user "charlie" at 12:15PM
  ;; and 19:15PM.  This runs from the user's home directory.
  #~(job '(next-minute-from (next-hour '(12 19)) '(15))
         (string-append #$idutils "/bin/mkid src")
         #:user "charlie"))

(operating-system
  ;; @dots{}
  (services (cons (mcron-service (list garbage-collector-job
                                       updatedb-job
                                       idutils-job))
                  %base-services)))
@end lisp

@xref{Guile Syntax, mcron job specifications,, mcron, GNU@tie{}mcron}, for
more information on mcron job specifications.  Below is the reference of the
mcron service.

On a running system, you can use the @code{schedule} action of the service
to visualize the mcron jobs that will be executed next:

@example
# herd schedule mcron
@end example

@noindent
The example above lists the next five tasks that will be executed, but you
can also specify the number of tasks to display:

@example
# herd schedule mcron 10
@end example

@deffn {Scheme Procedure} mcron-service @var{jobs} [#:mcron @var{mcron}]
Return an mcron service running @var{mcron} that schedules @var{jobs}, a
list of gexps denoting mcron job specifications.

This is a shorthand for:
@example
(service mcron-service-type
         (mcron-configuration (mcron mcron) (jobs jobs)))
@end example
@end deffn

@defvr {Scheme Variable} mcron-service-type
This is the type of the @code{mcron} service, whose value is an
@code{mcron-configuration} object.

This service type can be the target of a service extension that provides it
additional job specifications (@pxref{Dienstkompositionen}).  In other
words, it is possible to define services that provide additional mcron jobs
to run.
@end defvr

@deftp {Data Type} mcron-configuration
Data type representing the configuration of mcron.

@table @asis
@item @code{mcron} (default: @var{mcron})
The mcron package to use.

@item @code{jobs}
This is a list of gexps (@pxref{G-Ausdrücke}), where each gexp corresponds
to an mcron job specification (@pxref{Syntax, mcron job specifications,,
mcron, GNU@tie{}mcron}).
@end table
@end deftp


@node Log-Rotation
@subsubsection Log-Rotation

@cindex rottlog
@cindex log rotation
@cindex logging
Log files such as those found in @file{/var/log} tend to grow endlessly, so
it's a good idea to @dfn{rotate} them once in a while---i.e., archive their
contents in separate files, possibly compressed.  The @code{(gnu services
admin)} module provides an interface to GNU@tie{}Rot[t]log, a log rotation
tool (@pxref{Top,,, rottlog, GNU Rot[t]log Manual}).

The example below defines an operating system that provides log rotation
with the default settings, for commonly encountered log files.

@lisp
(use-modules (guix) (gnu))
(use-service-modules admin mcron)
(use-package-modules base idutils)

(operating-system
  ;; @dots{}
  (services (cons (service rottlog-service-type)
                  %base-services)))
@end lisp

@defvr {Scheme Variable} rottlog-service-type
This is the type of the Rottlog service, whose value is a
@code{rottlog-configuration} object.

Other services can extend this one with new @code{log-rotation} objects (see
below), thereby augmenting the set of files to be rotated.

This service type can define mcron jobs (@pxref{Geplante Auftragsausführung}) to
run the rottlog service.
@end defvr

@deftp {Data Type} rottlog-configuration
Data type representing the configuration of rottlog.

@table @asis
@item @code{rottlog} (default: @code{rottlog})
The Rottlog package to use.

@item @code{rc-file} (default: @code{(file-append rottlog "/etc/rc")})
The Rottlog configuration file to use (@pxref{Mandatory RC Variables,,,
rottlog, GNU Rot[t]log Manual}).

@item @code{rotations} (default: @code{%default-rotations})
A list of @code{log-rotation} objects as defined below.

@item @code{jobs}
This is a list of gexps where each gexp corresponds to an mcron job
specification (@pxref{Geplante Auftragsausführung}).
@end table
@end deftp

@deftp {Data Type} log-rotation
Data type representing the rotation of a group of log files.

Taking an example from the Rottlog manual (@pxref{Period Related File
Examples,,, rottlog, GNU Rot[t]log Manual}), a log rotation might be defined
like this:

@example
(log-rotation
  (frequency 'daily)
  (files '("/var/log/apache/*"))
  (options '("storedir apache-archives"
             "rotate 6"
             "notifempty"
             "nocompress")))
@end example

The list of fields is as follows:

@table @asis
@item @code{frequency} (default: @code{'weekly})
The log rotation frequency, a symbol.

@item @code{files}
The list of files or file glob patterns to rotate.

@item @code{options} (default: @code{'()})
The list of rottlog options for this rotation (@pxref{Configuration
parameters,,, rottlog, GNU Rot[t]lg Manual}).

@item @code{post-rotate} (default: @code{#f})
Either @code{#f} or a gexp to execute once the rotation has completed.
@end table
@end deftp

@defvr {Scheme Variable} %default-rotations
Specifies weekly rotation of @var{%rotated-files} and a couple of other
files.
@end defvr

@defvr {Scheme Variable} %rotated-files
The list of syslog-controlled files to be rotated.  By default it is:
@code{'("/var/log/messages" "/var/log/secure")}.
@end defvr

@node Netzwerkdienste
@subsubsection Netzwerkdienste

The @code{(gnu services networking)} module provides services to configure
the network interface.

@cindex DHCP, networking service
@defvr {Scheme Variable} dhcp-client-service-type
This is the type of services that run @var{dhcp}, a Dynamic Host
Configuration Protocol (DHCP) client, on all the non-loopback network
interfaces.  Its value is the DHCP client package to use, @code{isc-dhcp} by
default.
@end defvr

@deffn {Scheme Procedure} dhcpd-service-type
This type defines a service that runs a DHCP daemon.  To create a service of
this type, you must supply a @code{<dhcpd-configuration>}.  For example:

@example
(service dhcpd-service-type
         (dhcpd-configuration
          (config-file (local-file "my-dhcpd.conf"))
          (interfaces '("enp0s25"))))
@end example
@end deffn

@deftp {Data Type} dhcpd-configuration
@table @asis
@item @code{package} (default: @code{isc-dhcp})
The package that provides the DHCP daemon.  This package is expected to
provide the daemon at @file{sbin/dhcpd} relative to its output directory.
The default package is the @uref{http://www.isc.org/products/DHCP, ISC's
DHCP server}.
@item @code{config-file} (default: @code{#f})
The configuration file to use.  This is required.  It will be passed to
@code{dhcpd} via its @code{-cf} option.  This may be any ``file-like''
object (@pxref{G-Ausdrücke, file-like objects}).  See @code{man
dhcpd.conf} for details on the configuration file syntax.
@item @code{version} (default: @code{"4"})
The DHCP version to use.  The ISC DHCP server supports the values ``4'',
``6'', and ``4o6''.  These correspond to the @code{dhcpd} program options
@code{-4}, @code{-6}, and @code{-4o6}.  See @code{man dhcpd} for details.
@item @code{run-directory} (default: @code{"/run/dhcpd"})
The run directory to use.  At service activation time, this directory will
be created if it does not exist.
@item @code{pid-file} (default: @code{"/run/dhcpd/dhcpd.pid"})
The PID file to use.  This corresponds to the @code{-pf} option of
@code{dhcpd}.  See @code{man dhcpd} for details.
@item @code{interfaces} (default: @code{'()})
The names of the network interfaces on which dhcpd should listen for
broadcasts.  If this list is not empty, then its elements (which must be
strings) will be appended to the @code{dhcpd} invocation when starting the
daemon.  It may not be necessary to explicitly specify any interfaces here;
see @code{man dhcpd} for details.
@end table
@end deftp

@defvr {Scheme Variable} static-networking-service-type
@c TODO Document <static-networking> data structures.
This is the type for statically-configured network interfaces.
@end defvr

@deffn {Scheme Procedure} static-networking-service @var{interface} @var{ip} @
       [#:netmask #f] [#:gateway #f] [#:name-servers @code{'()}] @ [#:requirement
@code{'(udev)}] Return a service that starts @var{interface} with address
@var{ip}.  If @var{netmask} is true, use it as the network mask.  If
@var{gateway} is true, it must be a string specifying the default network
gateway.  @var{requirement} can be used to declare a dependency on another
service before configuring the interface.

This procedure can be called several times, one for each network interface
of interest.  Behind the scenes what it does is extend
@code{static-networking-service-type} with additional network interfaces to
handle.

For example:

@example
(static-networking-service "eno1" "192.168.1.82"
                           #:gateway "192.168.1.2"
                           #:name-servers '("192.168.1.2"))
@end example
@end deffn

@cindex wicd
@cindex wireless
@cindex WiFi
@cindex network management
@deffn {Scheme Procedure} wicd-service [#:wicd @var{wicd}]
Return a service that runs @url{https://launchpad.net/wicd,Wicd}, a network
management daemon that aims to simplify wired and wireless networking.

This service adds the @var{wicd} package to the global profile, providing
several commands to interact with the daemon and configure networking:
@command{wicd-client}, a graphical user interface, and the
@command{wicd-cli} and @command{wicd-curses} user interfaces.
@end deffn

@cindex ModemManager

@defvr {Scheme Variable} modem-manager-service-type
This is the service type for the
@uref{https://wiki.gnome.org/Projects/ModemManager, ModemManager}
service. The value for this service type is a
@code{modem-manager-configuration} record.

This service is part of @code{%desktop-services} (@pxref{Desktop-Dienste}).
@end defvr

@deftp {Data Type} modem-manager-configuration
Data type representing the configuration of ModemManager.

@table @asis
@item @code{modem-manager} (default: @code{modem-manager})
The ModemManager package to use.

@end table
@end deftp

@cindex NetworkManager

@defvr {Scheme Variable} network-manager-service-type
This is the service type for the
@uref{https://wiki.gnome.org/Projects/NetworkManager, NetworkManager}
service. The value for this service type is a
@code{network-manager-configuration} record.

This service is part of @code{%desktop-services} (@pxref{Desktop-Dienste}).
@end defvr

@deftp {Data Type} network-manager-configuration
Data type representing the configuration of NetworkManager.

@table @asis
@item @code{network-manager} (default: @code{network-manager})
The NetworkManager package to use.

@item @code{dns} (default: @code{"default"})
Processing mode for DNS, which affects how NetworkManager uses the
@code{resolv.conf} configuration file.

@table @samp
@item default
NetworkManager will update @code{resolv.conf} to reflect the nameservers
provided by currently active connections.

@item dnsmasq
NetworkManager will run @code{dnsmasq} as a local caching nameserver, using
a "split DNS" configuration if you are connected to a VPN, and then update
@code{resolv.conf} to point to the local nameserver.

@item none
NetworkManager will not modify @code{resolv.conf}.
@end table

@item @code{vpn-plugins} (default: @code{'()})
This is the list of available plugins for virtual private networks (VPNs).
An example of this is the @code{network-manager-openvpn} package, which
allows NetworkManager to manage VPNs @i{via} OpenVPN.

@end table
@end deftp

@cindex Connman
@deffn {Scheme Variable} connman-service-type
This is the service type to run @url{https://01.org/connman,Connman}, a
network connection manager.

Its value must be an @code{connman-configuration} record as in this example:

@example
(service connman-service-type
         (connman-configuration
           (disable-vpn? #t)))
@end example

See below for details about @code{connman-configuration}.
@end deffn

@deftp {Data Type} connman-configuration
Data Type representing the configuration of connman.

@table @asis
@item @code{connman} (default: @var{connman})
The connman package to use.

@item @code{disable-vpn?} (default: @code{#f})
When true, enable connman's vpn plugin.
@end table
@end deftp

@cindex WPA Supplicant
@defvr {Scheme Variable} wpa-supplicant-service-type
This is the service type to run @url{https://w1.fi/wpa_supplicant/,WPA
supplicant}, an authentication daemon required to authenticate against
encrypted WiFi or ethernet networks.
@end defvr

@deftp {Data Type} wpa-supplicant-configuration
Data type representing the configuration of WPA Supplicant.

It takes the following parameters:

@table @asis
@item @code{wpa-supplicant} (default: @code{wpa-supplicant})
The WPA Supplicant package to use.

@item @code{dbus?} (default: @code{#t})
Whether to listen for requests on D-Bus.

@item @code{pid-file} (default: @code{"/var/run/wpa_supplicant.pid"})
Where to store the PID file.

@item @code{interface} (default: @code{#f})
If this is set, it must specify the name of a network interface that WPA
supplicant will control.

@item @code{config-file} (default: @code{#f})
Optional configuration file to use.

@item @code{extra-options} (default: @code{'()})
List of additional command-line arguments to pass to the daemon.
@end table
@end deftp

@cindex iptables
@defvr {Scheme Variable} iptables-service-type
This is the service type to set up an iptables configuration. iptables is a
packet filtering framework supported by the Linux kernel.  This service
supports configuring iptables for both IPv4 and IPv6.  A simple example
configuration rejecting all incoming connections except those to the ssh
port 22 is shown below.

@lisp
(service iptables-service-type
         (iptables-configuration
          (ipv4-rules (plain-file "iptables.rules" "*filter
:INPUT ACCEPT
:FORWARD ACCEPT
:OUTPUT ACCEPT
-A INPUT -p tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-port-unreachable
COMMIT
"))
          (ipv6-rules (plain-file "ip6tables.rules" "*filter
:INPUT ACCEPT
:FORWARD ACCEPT
:OUTPUT ACCEPT
-A INPUT -p tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp6-port-unreachable
COMMIT
"))))
@end lisp
@end defvr

@deftp {Data Type} iptables-configuration
The data type representing the configuration of iptables.

@table @asis
@item @code{iptables} (default: @code{iptables})
The iptables package that provides @code{iptables-restore} and
@code{ip6tables-restore}.
@item @code{ipv4-rules} (default: @code{%iptables-accept-all-rules})
The iptables rules to use.  It will be passed to @code{iptables-restore}.
This may be any ``file-like'' object (@pxref{G-Ausdrücke, file-like
objects}).
@item @code{ipv6-rules} (default: @code{%iptables-accept-all-rules})
The ip6tables rules to use.  It will be passed to @code{ip6tables-restore}.
This may be any ``file-like'' object (@pxref{G-Ausdrücke, file-like
objects}).
@end table
@end deftp

@cindex NTP (Network Time Protocol), service
@cindex real time clock
@defvr {Scheme Variable} ntp-service-type
This is the type of the service running the the @uref{http://www.ntp.org,
Network Time Protocol (NTP)} daemon, @command{ntpd}.  The daemon will keep
the system clock synchronized with that of the specified NTP servers.

The value of this service is an @code{ntpd-configuration} object, as
described below.
@end defvr

@deftp {Data Type} ntp-configuration
This is the data type for the NTP service configuration.

@table @asis
@item @code{servers} (default: @code{%ntp-servers})
This is the list of servers (host names) with which @command{ntpd} will be
synchronized.

@item @code{allow-large-adjustment?} (default: @code{#f})
This determines whether @command{ntpd} is allowed to make an initial
adjustment of more than 1,000 seconds.

@item @code{ntp} (default: @code{ntp})
The NTP package to use.
@end table
@end deftp

@defvr {Scheme Variable} %ntp-servers
List of host names used as the default NTP servers.  These are servers of
the @uref{https://www.ntppool.org/en/, NTP Pool Project}.
@end defvr

@cindex OpenNTPD
@deffn {Scheme Procedure} openntpd-service-type
Run the @command{ntpd}, the Network Time Protocol (NTP) daemon, as
implemented by @uref{http://www.openntpd.org, OpenNTPD}.  The daemon will
keep the system clock synchronized with that of the given servers.

@example
(service
 openntpd-service-type
 (openntpd-configuration
  (listen-on '("127.0.0.1" "::1"))
  (sensor '("udcf0 correction 70000"))
  (constraint-from '("www.gnu.org"))
  (constraints-from '("https://www.google.com/"))
  (allow-large-adjustment? #t)))

@end example
@end deffn

@deftp {Data Type} openntpd-configuration
@table @asis
@item @code{openntpd} (default: @code{(file-append openntpd "/sbin/ntpd")})
The openntpd executable to use.
@item @code{listen-on} (default: @code{'("127.0.0.1" "::1")})
A list of local IP addresses or hostnames the ntpd daemon should listen on.
@item @code{query-from} (default: @code{'()})
A list of local IP address the ntpd daemon should use for outgoing queries.
@item @code{sensor} (default: @code{'()})
Specify a list of timedelta sensor devices ntpd should use.  @code{ntpd}
will listen to each sensor that acutally exists and ignore non-existant
ones.  See @uref{https://man.openbsd.org/ntpd.conf, upstream documentation}
for more information.
@item @code{server} (default: @var{%ntp-servers})
Specify a list of IP addresses or hostnames of NTP servers to synchronize
to.
@item @code{servers} (default: @code{'()})
Specify a list of IP addresses or hostnames of NTP pools to synchronize to.
@item @code{constraint-from} (default: @code{'()})
@code{ntpd} can be configured to query the ‘Date’ from trusted HTTPS servers
via TLS.  This time information is not used for precision but acts as an
authenticated constraint, thereby reducing the impact of unauthenticated NTP
man-in-the-middle attacks.  Specify a list of URLs, IP addresses or
hostnames of HTTPS servers to provide a constraint.
@item @code{constraints-from} (default: @code{'()})
As with constraint from, specify a list of URLs, IP addresses or hostnames
of HTTPS servers to provide a constraint.  Should the hostname resolve to
multiple IP addresses, @code{ntpd} will calculate a median constraint from
all of them.
@item @code{allow-large-adjustment?} (default: @code{#f})
Determines if @code{ntpd} is allowed to make an initial adjustment of more
than 180 seconds.
@end table
@end deftp

@cindex inetd
@deffn {Scheme variable} inetd-service-type
This service runs the @command{inetd} (@pxref{inetd invocation,,, inetutils,
GNU Inetutils}) daemon.  @command{inetd} listens for connections on internet
sockets, and lazily starts the specified server program when a connection is
made on one of these sockets.

The value of this service is an @code{inetd-configuration} object.  The
following example configures the @command{inetd} daemon to provide the
built-in @command{echo} service, as well as an smtp service which forwards
smtp traffic over ssh to a server @code{smtp-server} behind a gateway
@code{hostname}:

@example
(service
 inetd-service-type
 (inetd-configuration
  (entries (list
            (inetd-entry
             (name "echo")
             (socket-type 'stream)
             (protocol "tcp")
             (wait? #f)
             (user "root"))
            (inetd-entry
             (node "127.0.0.1")
             (name "smtp")
             (socket-type 'stream)
             (protocol "tcp")
             (wait? #f)
             (user "root")
             (program (file-append openssh "/bin/ssh"))
             (arguments
              '("ssh" "-qT" "-i" "/path/to/ssh_key"
                "-W" "smtp-server:25" "user@@hostname")))))
@end example

See below for more details about @code{inetd-configuration}.
@end deffn

@deftp {Data Type} inetd-configuration
Data type representing the configuration of @command{inetd}.

@table @asis
@item @code{program} (default: @code{(file-append inetutils "/libexec/inetd")})
The @command{inetd} executable to use.

@item @code{entries} (default: @code{'()})
A list of @command{inetd} service entries.  Each entry should be created by
the @code{inetd-entry} constructor.
@end table
@end deftp

@deftp {Data Type} inetd-entry
Data type representing an entry in the @command{inetd} configuration.  Each
entry corresponds to a socket where @command{inetd} will listen for
requests.

@table @asis
@item @code{node} (Vorgabe: @code{#f})
Optional string, a comma-separated list of local addresses @command{inetd}
should use when listening for this service.  @xref{Configuration file,,,
inetutils, GNU Inetutils} for a complete description of all options.
@item @code{name}
A string, the name must correspond to an entry in @code{/etc/services}.
@item @code{socket-type}
One of @code{'stream}, @code{'dgram}, @code{'raw}, @code{'rdm} or
@code{'seqpacket}.
@item @code{protocol}
A string, must correspond to an entry in @code{/etc/protocols}.
@item @code{wait?} (Vorgabe: @code{#t})
Whether @command{inetd} should wait for the server to exit before listening
to new service requests.
@item @code{user}
A string containing the user (and, optionally, group) name of the user as
whom the server should run.  The group name can be specified in a suffix,
separated by a colon or period, i.e. @code{"user"}, @code{"user:group"} or
@code{"user.group"}.
@item @code{program} (default: @code{"internal"})
The server program which will serve the requests, or @code{"internal"} if
@command{inetd} should use a built-in service.
@item @code{arguments} (default: @code{'()})
A list strings or file-like objects, which are the server program's
arguments, starting with the zeroth argument, i.e. the name of the program
itself.  For @command{inetd}'s internal services, this entry must be
@code{'()} or @code{'("internal")}.
@end table

@xref{Configuration file,,, inetutils, GNU Inetutils} for a more detailed
discussion of each configuration field.
@end deftp

@cindex Tor
@defvr {Scheme Variable} tor-service-type
This is the type for a service that runs the @uref{https://torproject.org,
Tor} anonymous networking daemon.  The service is configured using a
@code{<tor-configuration>} record.  By default, the Tor daemon runs as the
@code{tor} unprivileged user, which is a member of the @code{tor} group.

@end defvr

@deffn {Scheme Procedure} tor-service [@var{config-file}] [#:tor @var{tor}]
This procedure is deprecated and will be removed in a future release.
Return a service of the @code{tor-service-type} type.  @var{config-file} and
@var{tor} have the same meaning as in @code{<tor-configuration>}.
@end deffn

@deftp {Data Type} tor-configuration
@table @asis
@item @code{tor} (default: @code{tor})
The package that provides the Tor daemon.  This package is expected to
provide the daemon at @file{bin/tor} relative to its output directory.  The
default package is the @uref{https://www.torproject.org, Tor Project's}
implementation.

@item @code{config-file} (default: @code{(plain-file "empty" "")})
The configuration file to use.  It will be appended to a default
configuration file, and the final configuration file will be passed to
@code{tor} via its @code{-f} option.  This may be any ``file-like'' object
(@pxref{G-Ausdrücke, file-like objects}).  See @code{man tor} for details
on the configuration file syntax.

@item @code{hidden-services} (default: @code{'()})
The list of @code{<hidden-service>} records to use.  For any hidden service
you include in this list, appropriate configuration to enable the hidden
service will be automatically added to the default configuration file.  You
may conveniently create @code{<hidden-service>} records using the
@code{tor-hidden-service} procedure described below.

@item @code{socks-socket-type} (default: @code{'tcp})
The default socket type that Tor should use for its SOCKS socket.  This must
be either @code{'tcp} or @code{'unix}.  If it is @code{'tcp}, then by
default Tor will listen on TCP port 9050 on the loopback interface (i.e.,
localhost).  If it is @code{'unix}, then Tor will listen on the UNIX domain
socket @file{/var/run/tor/socks-sock}, which will be made writable by
members of the @code{tor} group.

If you want to customize the SOCKS socket in more detail, leave
@code{socks-socket-type} at its default value of @code{'tcp} and use
@code{config-file} to override the default by providing your own
@code{SocksPort} option.
@end table
@end deftp

@cindex hidden service
@deffn {Scheme Procedure} tor-hidden-service @var{name} @var{mapping}
Define a new Tor @dfn{hidden service} called @var{name} and implementing
@var{mapping}.  @var{mapping} is a list of port/host tuples, such as:

@example
 '((22 "127.0.0.1:22")
   (80 "127.0.0.1:8080"))
@end example

In this example, port 22 of the hidden service is mapped to local port 22,
and port 80 is mapped to local port 8080.

This creates a @file{/var/lib/tor/hidden-services/@var{name}} directory,
where the @file{hostname} file contains the @code{.onion} host name for the
hidden service.

See @uref{https://www.torproject.org/docs/tor-hidden-service.html.en, the
Tor project's documentation} for more information.
@end deffn

The @code{(gnu services rsync)} module provides the following services:

You might want an rsync daemon if you have files that you want available so
anyone (or just yourself) can download existing files or upload new files.

@deffn {Scheme Variable} rsync-service-type
This is the type for the @uref{https://rsync.samba.org, rsync} rsync daemon,
@command{rsync-configuration} record as in this example:

@example
(service rsync-service-type)
@end example

See below for details about @code{rsync-configuration}.
@end deffn

@deftp {Data Type} rsync-configuration
Data type representing the configuration for @code{rsync-service}.

@table @asis
@item @code{package} (default: @var{rsync})
@code{rsync} package to use.

@item @code{port-number} (default: @code{873})
TCP port on which @command{rsync} listens for incoming connections.  If port
is less than @code{1024} @command{rsync} needs to be started as the
@code{root} user and group.

@item @code{pid-file} (default: @code{"/var/run/rsyncd/rsyncd.pid"})
Name of the file where @command{rsync} writes its PID.

@item @code{lock-file} (default: @code{"/var/run/rsyncd/rsyncd.lock"})
Name of the file where @command{rsync} writes its lock file.

@item @code{log-file} (default: @code{"/var/log/rsyncd.log"})
Name of the file where @command{rsync} writes its log file.

@item @code{use-chroot?} (default: @var{#t})
Whether to use chroot for @command{rsync} shared directory.

@item @code{share-path} (default: @file{/srv/rsync})
Location of the @command{rsync} shared directory.

@item @code{share-comment} (default: @code{"Rsync share"})
Comment of the @command{rsync} shared directory.

@item @code{read-only?} (default: @var{#f})
Read-write permissions to shared directory.

@item @code{timeout} (default: @code{300})
I/O timeout in seconds.

@item @code{user} (default: @var{"root"})
Owner of the @code{rsync} process.

@item @code{group} (default: @var{"root"})
Group of the @code{rsync} process.

@item @code{uid} (default: @var{"rsyncd"})
User name or user ID that file transfers to and from that module should take
place as when the daemon was run as @code{root}.

@item @code{gid} (default: @var{"rsyncd"})
Group name or group ID that will be used when accessing the module.

@end table
@end deftp

Furthermore, @code{(gnu services ssh)} provides the following services.
@cindex SSH
@cindex SSH server

@deffn {Scheme Procedure} lsh-service [#:host-key "/etc/lsh/host-key"] @
       [#:daemonic? #t] [#:interfaces '()] [#:port-number 22] @
[#:allow-empty-passwords? #f] [#:root-login? #f] @ [#:syslog-output? #t]
[#:x11-forwarding? #t] @ [#:tcp/ip-forwarding? #t]
[#:password-authentication? #t] @ [#:public-key-authentication? #t]
[#:initialize? #t] Run the @command{lshd} program from @var{lsh} to listen
on port @var{port-number}.  @var{host-key} must designate a file containing
the host key, and readable only by root.

When @var{daemonic?} is true, @command{lshd} will detach from the
controlling terminal and log its output to syslogd, unless one sets
@var{syslog-output?} to false.  Obviously, it also makes lsh-service depend
on existence of syslogd service.  When @var{pid-file?} is true,
@command{lshd} writes its PID to the file called @var{pid-file}.

When @var{initialize?} is true, automatically create the seed and host key
upon service activation if they do not exist yet.  This may take long and
require interaction.

When @var{initialize?} is false, it is up to the user to initialize the
randomness generator (@pxref{lsh-make-seed,,, lsh, LSH Manual}), and to
create a key pair with the private key stored in file @var{host-key}
(@pxref{lshd basics,,, lsh, LSH Manual}).

When @var{interfaces} is empty, lshd listens for connections on all the
network interfaces; otherwise, @var{interfaces} must be a list of host names
or addresses.

@var{allow-empty-passwords?} specifies whether to accept log-ins with empty
passwords, and @var{root-login?} specifies whether to accept log-ins as
root.

The other options should be self-descriptive.
@end deffn

@cindex SSH
@cindex SSH server
@deffn {Scheme Variable} openssh-service-type
This is the type for the @uref{http://www.openssh.org, OpenSSH} secure shell
daemon, @command{sshd}.  Its value must be an @code{openssh-configuration}
record as in this example:

@example
(service openssh-service-type
         (openssh-configuration
           (x11-forwarding? #t)
           (permit-root-login 'without-password)
           (authorized-keys
             `(("alice" ,(local-file "alice.pub"))
               ("bob" ,(local-file "bob.pub"))))))
@end example

See below for details about @code{openssh-configuration}.

This service can be extended with extra authorized keys, as in this example:

@example
(service-extension openssh-service-type
                   (const `(("charlie"
                             ,(local-file "charlie.pub")))))
@end example
@end deffn

@deftp {Data Type} openssh-configuration
This is the configuration record for OpenSSH's @command{sshd}.

@table @asis
@item @code{pid-file} (default: @code{"/var/run/sshd.pid"})
Name of the file where @command{sshd} writes its PID.

@item @code{port-number} (default: @code{22})
TCP port on which @command{sshd} listens for incoming connections.

@item @code{permit-root-login} (default: @code{#f})
This field determines whether and when to allow logins as root.  If
@code{#f}, root logins are disallowed; if @code{#t}, they are allowed.  If
it's the symbol @code{'without-password}, then root logins are permitted but
not with password-based authentication.

@item @code{allow-empty-passwords?} (default: @code{#f})
When true, users with empty passwords may log in.  When false, they may not.

@item @code{password-authentication?} (default: @code{#t})
When true, users may log in with their password.  When false, they have
other authentication methods.

@item @code{public-key-authentication?} (default: @code{#t})
When true, users may log in using public key authentication.  When false,
users have to use other authentication method.

Authorized public keys are stored in @file{~/.ssh/authorized_keys}.  This is
used only by protocol version 2.

@item @code{x11-forwarding?} (default: @code{#f})
When true, forwarding of X11 graphical client connections is enabled---in
other words, @command{ssh} options @option{-X} and @option{-Y} will work.

@item @code{allow-agent-forwarding?} (default: @code{#t})
Whether to allow agent forwarding.

@item @code{allow-tcp-forwarding?} (default: @code{#t})
Whether to allow TCP forwarding.

@item @code{gateway-ports?} (default: @code{#f})
Whether to allow gateway ports.

@item @code{challenge-response-authentication?} (default: @code{#f})
Specifies whether challenge response authentication is allowed (e.g. via
PAM).

@item @code{use-pam?} (default: @code{#t})
Enables the Pluggable Authentication Module interface.  If set to @code{#t},
this will enable PAM authentication using
@code{challenge-response-authentication?} and
@code{password-authentication?}, in addition to PAM account and session
module processing for all authentication types.

Because PAM challenge response authentication usually serves an equivalent
role to password authentication, you should disable either
@code{challenge-response-authentication?} or
@code{password-authentication?}.

@item @code{print-last-log?} (default: @code{#t})
Specifies whether @command{sshd} should print the date and time of the last
user login when a user logs in interactively.

@item @code{subsystems} (default: @code{'(("sftp" "internal-sftp"))})
Configures external subsystems (e.g. file transfer daemon).

This is a list of two-element lists, each of which containing the subsystem
name and a command (with optional arguments) to execute upon subsystem
request.

The command @command{internal-sftp} implements an in-process SFTP server.
Alternately, one can specify the @command{sftp-server} command:
@example
(service openssh-service-type
         (openssh-configuration
          (subsystems
           `(("sftp" ,(file-append openssh "/libexec/sftp-server"))))))
@end example

@item @code{accepted-environment} (default: @code{'()})
List of strings describing which environment variables may be exported.

Each string gets on its own line.  See the @code{AcceptEnv} option in
@code{man sshd_config}.

This example allows ssh-clients to export the @code{COLORTERM} variable.  It
is set by terminal emulators, which support colors.  You can use it in your
shell's ressource file to enable colors for the prompt and commands if this
variable is set.

@example
(service openssh-service-type
         (openssh-configuration
           (accepted-environment '("COLORTERM"))))
@end example

@item @code{authorized-keys} (default: @code{'()})
@cindex authorized keys, SSH
@cindex SSH authorized keys
This is the list of authorized keys.  Each element of the list is a user
name followed by one or more file-like objects that represent SSH public
keys.  For example:

@example
(openssh-configuration
  (authorized-keys
    `(("rekado" ,(local-file "rekado.pub"))
      ("chris" ,(local-file "chris.pub"))
      ("root" ,(local-file "rekado.pub") ,(local-file "chris.pub")))))
@end example

@noindent
registers the specified public keys for user accounts @code{rekado},
@code{chris}, and @code{root}.

Additional authorized keys can be specified @i{via}
@code{service-extension}.

Note that this does @emph{not} interfere with the use of
@file{~/.ssh/authorized_keys}.

@item @code{log-level} (default: @code{'info})
This is a symbol specifying the logging level: @code{quiet}, @code{fatal},
@code{error}, @code{info}, @code{verbose}, @code{debug}, etc.  See the man
page for @file{sshd_config} for the full list of level names.

@end table
@end deftp

@deffn {Scheme Procedure} dropbear-service [@var{config}]
Run the @uref{https://matt.ucc.asn.au/dropbear/dropbear.html,Dropbear SSH
daemon} with the given @var{config}, a @code{<dropbear-configuration>}
object.

For example, to specify a Dropbear service listening on port 1234, add this
call to the operating system's @code{services} field:

@example
(dropbear-service (dropbear-configuration
                    (port-number 1234)))
@end example
@end deffn

@deftp {Data Type} dropbear-configuration
This data type represents the configuration of a Dropbear SSH daemon.

@table @asis
@item @code{dropbear} (default: @var{dropbear})
The Dropbear package to use.

@item @code{port-number} (default: 22)
The TCP port where the daemon waits for incoming connections.

@item @code{syslog-output?} (default: @code{#t})
Whether to enable syslog output.

@item @code{pid-file} (default: @code{"/var/run/dropbear.pid"})
File name of the daemon's PID file.

@item @code{root-login?} (default: @code{#f})
Whether to allow @code{root} logins.

@item @code{allow-empty-passwords?} (default: @code{#f})
Whether to allow empty passwords.

@item @code{password-authentication?} (default: @code{#t})
Whether to enable password-based authentication.
@end table
@end deftp

@defvr {Scheme Variable} %facebook-host-aliases
This variable contains a string for use in @file{/etc/hosts} (@pxref{Host
Names,,, libc, The GNU C Library Reference Manual}).  Each line contains a
entry that maps a known server name of the Facebook on-line service---e.g.,
@code{www.facebook.com}---to the local host---@code{127.0.0.1} or its IPv6
equivalent, @code{::1}.

This variable is typically used in the @code{hosts-file} field of an
@code{operating-system} declaration (@pxref{„operating-system“-Referenz,
@file{/etc/hosts}}):

@example
(use-modules (gnu) (guix))

(operating-system
  (host-name "mymachine")
  ;; ...
  (hosts-file
    ;; Create a /etc/hosts file with aliases for "localhost"
    ;; and "mymachine", as well as for Facebook servers.
    (plain-file "hosts"
                (string-append (local-host-aliases host-name)
                               %facebook-host-aliases))))
@end example

This mechanism can prevent programs running locally, such as Web browsers,
from accessing Facebook.
@end defvr

The @code{(gnu services avahi)} provides the following definition.

@deffn {Scheme Procedure} avahi-service [#:avahi @var{avahi}] @
          [#:host-name #f] [#:publish? #t] [#:ipv4? #t] @ [#:ipv6? #t] [#:wide-area?
#f] @ [#:domains-to-browse '()] [#:debug? #f] Return a service that runs
@command{avahi-daemon}, a system-wide mDNS/DNS-SD responder that allows for
service discovery and "zero-configuration" host name lookups (see
@uref{http://avahi.org/}), and extends the name service cache daemon (nscd)
so that it can resolve @code{.local} host names using
@uref{http://0pointer.de/lennart/projects/nss-mdns/, nss-mdns}.
Additionally, add the @var{avahi} package to the system profile so that
commands such as @command{avahi-browse} are directly usable.

If @var{host-name} is different from @code{#f}, use that as the host name to
publish for this machine; otherwise, use the machine's actual host name.

When @var{publish?} is true, publishing of host names and services is
allowed; in particular, avahi-daemon will publish the machine's host name
and IP address via mDNS on the local network.

When @var{wide-area?} is true, DNS-SD over unicast DNS is enabled.

Boolean values @var{ipv4?} and @var{ipv6?} determine whether to use
IPv4/IPv6 sockets.
@end deffn

@deffn {Scheme Variable} openvswitch-service-type
This is the type of the @uref{http://www.openvswitch.org, Open vSwitch}
service, whose value should be an @code{openvswitch-configuration} object.
@end deffn

@deftp {Data Type} openvswitch-configuration
Data type representing the configuration of Open vSwitch, a multilayer
virtual switch which is designed to enable massive network automation
through programmatic extension.

@table @asis
@item @code{package} (default: @var{openvswitch})
Package object of the Open vSwitch.

@end table
@end deftp

@node X Window
@subsubsection X Window

@cindex X11
@cindex X Window System
@cindex login manager
Support for the X Window graphical display system---specifically Xorg---is
provided by the @code{(gnu services xorg)} module.  Note that there is no
@code{xorg-service} procedure.  Instead, the X server is started by the
@dfn{login manager}, by default SLiM.

@cindex window manager
To use X11, you must install at least one @dfn{window manager}---for example
the @code{windowmaker} or @code{openbox} packages---preferably by adding it
to the @code{packages} field of your operating system definition
(@pxref{„operating-system“-Referenz, system-wide packages}).

@defvr {Scheme Variable} slim-service-type
This is the type for the SLiM graphical login manager for X11.

@cindex session types (X11)
@cindex X11 session types
SLiM looks for @dfn{session types} described by the @file{.desktop} files in
@file{/run/current-system/profile/share/xsessions} and allows users to
choose a session from the log-in screen using @kbd{F1}.  Packages such as
@code{xfce}, @code{sawfish}, and @code{ratpoison} provide @file{.desktop}
files; adding them to the system-wide set of packages automatically makes
them available at the log-in screen.

In addition, @file{~/.xsession} files are honored.  When available,
@file{~/.xsession} must be an executable that starts a window manager and/or
other X clients.
@end defvr

@deftp {Data Type} slim-configuration
Data type representing the configuration of @code{slim-service-type}.

@table @asis
@item @code{allow-empty-passwords?} (default: @code{#t})
Whether to allow logins with empty passwords.

@item @code{auto-login?} (default: @code{#f})
@itemx @code{default-user} (default: @code{""})
When @code{auto-login?} is false, SLiM presents a log-in screen.

When @code{auto-login?} is true, SLiM logs in directly as
@code{default-user}.

@item @code{theme} (default: @code{%default-slim-theme})
@itemx @code{theme-name} (default: @code{%default-slim-theme-name})
The graphical theme to use and its name.

@item @code{auto-login-session} (default: @code{#f})
If true, this must be the name of the executable to start as the default
session---e.g., @code{(file-append windowmaker "/bin/windowmaker")}.

If false, a session described by one of the available @file{.desktop} files
in @code{/run/current-system/profile} and @code{~/.guix-profile} will be
used.

@quotation Anmerkung
You must install at least one window manager in the system profile or in
your user profile.  Failing to do that, if @code{auto-login-session} is
false, you will be unable to log in.
@end quotation

@item @code{startx} (default: @code{(xorg-start-command)})
The command used to start the X11 graphical server.

@item @code{xauth} (default: @code{xauth})
The XAuth package to use.

@item @code{shepherd} (default: @code{shepherd})
The Shepherd package used when invoking @command{halt} and @command{reboot}.

@item @code{sessreg} (default: @code{sessreg})
The sessreg package used in order to register the session.

@item @code{slim} (default: @code{slim})
The SLiM package to use.
@end table
@end deftp

@defvr {Scheme Variable} %default-theme
@defvrx {Scheme Variable} %default-theme-name
The default SLiM theme and its name.
@end defvr


@deftp {Data Type} sddm-configuration
This is the data type representing the sddm service configuration.

@table @asis
@item @code{display-server} (default: "x11")
Select display server to use for the greeter. Valid values are "x11" or
"wayland".

@item @code{numlock} (default: "on")
Valid values are "on", "off" or "none".

@item @code{halt-command} (default @code{#~(string-apppend #$shepherd "/sbin/halt")})
Command to run when halting.

@item @code{reboot-command} (default @code{#~(string-append #$shepherd "/sbin/reboot")})
Command to run when rebooting.

@item @code{theme} (default "maldives")
Theme to use. Default themes provided by SDDM are "elarun" or "maldives".

@item @code{themes-directory} (default "/run/current-system/profile/share/sddm/themes")
Directory to look for themes.

@item @code{faces-directory} (default "/run/current-system/profile/share/sddm/faces")
Directory to look for faces.

@item @code{default-path} (default "/run/current-system/profile/bin")
Default PATH to use.

@item @code{minimum-uid} (default 1000)
Minimum UID to display in SDDM.

@item @code{maximum-uid} (default 2000)
Maximum UID to display in SDDM

@item @code{remember-last-user?} (default #t)
Remember last user.

@item @code{remember-last-session?} (default #t)
Remember last session.

@item @code{hide-users} (default "")
Usernames to hide from SDDM greeter.

@item @code{hide-shells} (default @code{#~(string-append #$shadow "/sbin/nologin")})
Users with shells listed will be hidden from the SDDM greeter.

@item @code{session-command} (default @code{#~(string-append #$sddm "/share/sddm/scripts/wayland-session")})
Script to run before starting a wayland session.

@item @code{sessions-directory} (default "/run/current-system/profile/share/wayland-sessions")
Directory to look for desktop files starting wayland sessions.

@item @code{xorg-server-path} (default @code{xorg-start-command})
Path to xorg-server.

@item @code{xauth-path} (default @code{#~(string-append #$xauth "/bin/xauth")})
Path to xauth.

@item @code{xephyr-path} (default @code{#~(string-append #$xorg-server "/bin/Xephyr")})
Path to Xephyr.

@item @code{xdisplay-start} (default @code{#~(string-append #$sddm "/share/sddm/scripts/Xsetup")})
Script to run after starting xorg-server.

@item @code{xdisplay-stop} (default @code{#~(string-append #$sddm "/share/sddm/scripts/Xstop")})
Script to run before stopping xorg-server.

@item @code{xsession-command} (default: @code{xinitrc})
Script to run before starting a X session.

@item @code{xsessions-directory} (default: "/run/current-system/profile/share/xsessions")
Directory to look for desktop files starting X sessions.

@item @code{minimum-vt} (default: 7)
Minimum VT to use.

@item @code{xserver-arguments} (default "-nolisten tcp")
Arguments to pass to xorg-server.

@item @code{auto-login-user} (default "")
User to use for auto-login.

@item @code{auto-login-session} (default "")
Desktop file to use for auto-login.

@item @code{relogin?} (default #f)
Relogin after logout.

@end table
@end deftp

@cindex login manager
@cindex X11 login
@deffn {Scheme Procedure} sddm-service config
Return a service that spawns the SDDM graphical login manager for config of
type @code{<sddm-configuration>}.

@example
  (sddm-service (sddm-configuration
                 (auto-login-user "Alice")
                 (auto-login-session "xfce.desktop")))
@end example
@end deffn

@deffn {Scheme Procedure} xorg-start-command [#:guile] @
  [#:modules %default-xorg-modules] @ [#:fonts %default-xorg-fonts] @
[#:configuration-file (xorg-configuration-file @dots{})] @ [#:xorg-server
@var{xorg-server}] Return a @code{startx} script in which @var{modules}, a
list of X module packages, and @var{fonts}, a list of X font directories,
are available.  See @code{xorg-wrapper} for more details on the arguments.
The result should be used in place of @code{startx}.

Usually the X server is started by a login manager.
@end deffn

@deffn {Scheme Procedure} xorg-configuration-file @
  [#:modules %default-xorg-modules] @ [#:fonts %default-xorg-fonts] @
[#:drivers '()] [#:resolutions '()] [#:extra-config '()] Return a
configuration file for the Xorg server containing search paths for all the
common drivers.

@var{modules} must be a list of @dfn{module packages} loaded by the Xorg
server---e.g., @code{xf86-video-vesa}, @code{xf86-input-keyboard}, and so
on.  @var{fonts} must be a list of font directories to add to the server's
@dfn{font path}.

@var{drivers} must be either the empty list, in which case Xorg chooses a
graphics driver automatically, or a list of driver names that will be tried
in this order---e.g., @code{("modesetting" "vesa")}.

Likewise, when @var{resolutions} is the empty list, Xorg chooses an
appropriate screen resolution; otherwise, it must be a list of
resolutions---e.g., @code{((1024 768) (640 480))}.

Last, @var{extra-config} is a list of strings or objects appended to the
configuration file.  It is used to pass extra text to be added verbatim to
the configuration file.

@cindex keymap
@cindex keyboard layout
This procedure is especially useful to configure a different keyboard layout
than the default US keymap.  For instance, to use the ``bépo'' keymap by
default on the display manager:

@example
(define bepo-evdev
  "Section \"InputClass\"
        Identifier \"evdev keyboard catchall\"
        Driver \"evdev\"
        MatchIsKeyboard \"on\"
        Option \"xkb_layout\" \"fr\"
        Option \"xkb_variant\" \"bepo\"
EndSection")

(operating-system
  ...
  (services
    (modify-services %desktop-services
      (slim-service-type config =>
        (slim-configuration
          (inherit config)
          (startx (xorg-start-command
                   #:configuration-file
                   (xorg-configuration-file
                     #:extra-config
                     (list bepo-evdev)))))))))
@end example

The @code{MatchIsKeyboard} line specifies that we only apply the
configuration to keyboards.  Without this line, other devices such as
touchpad may not work correctly because they will be attached to the wrong
driver.  In this example, the user typically used @code{setxkbmap fr bepo}
to set their favorite keymap once logged in.  The first argument corresponds
to the layout, while the second argument corresponds to the variant.  The
@code{xkb_variant} line can be omitted to select the default variant.
@end deffn

@deffn {Scheme Procedure} screen-locker-service @var{package} [@var{program}]
Add @var{package}, a package for a screen locker or screen saver whose
command is @var{program}, to the set of setuid programs and add a PAM entry
for it.  For example:

@lisp
(screen-locker-service xlockmore "xlock")
@end lisp

makes the good ol' XlockMore usable.
@end deffn


@node Druckdienste
@subsubsection Druckdienste

@cindex printer support with CUPS
The @code{(gnu services cups)} module provides a Guix service definition for
the CUPS printing service.  To add printer support to a GuixSD system, add a
@code{cups-service} to the operating system definition:

@deffn {Scheme Variable} cups-service-type
The service type for the CUPS print server.  Its value should be a valid
CUPS configuration (see below).  To use the default settings, simply write:
@example
(service cups-service-type)
@end example
@end deffn

The CUPS configuration controls the basic things about your CUPS
installation: what interfaces it listens on, what to do if a print job
fails, how much logging to do, and so on.  To actually add a printer, you
have to visit the @url{http://localhost:631} URL, or use a tool such as
GNOME's printer configuration services.  By default, configuring a CUPS
service will generate a self-signed certificate if needed, for secure
connections to the print server.

Suppose you want to enable the Web interface of CUPS and also add support
for Epson printers @i{via} the @code{escpr} package and for HP printers
@i{via} the @code{hplip-minimal} package.  You can do that directly, like
this (you need to use the @code{(gnu packages cups)} module):

@example
(service cups-service-type
         (cups-configuration
           (web-interface? #t)
           (extensions
             (list cups-filters escpr hplip-minimal))))
@end example

Note: If you wish to use the Qt5 based GUI which comes with the hplip
package then it is suggested that you install the @code{hplip} package,
either in your OS configuration file or as your user.

The available configuration parameters follow.  Each parameter definition is
preceded by its type; for example, @samp{string-list foo} indicates that the
@code{foo} parameter should be specified as a list of strings.  There is
also a way to specify the configuration as a string, if you have an old
@code{cupsd.conf} file that you want to port over from some other system;
see the end for more details.

@c The following documentation was initially generated by
@c (generate-documentation) in (gnu services cups).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as CUPS updates.


Available @code{cups-configuration} fields are:

@deftypevr {@code{cups-configuration} parameter} package cups
The CUPS package.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} package-list extensions
Drivers and other extensions to the CUPS package.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} files-configuration files-configuration
Configuration of where to write logs, what directories to use for print
spools, and related privileged configuration parameters.

Available @code{files-configuration} fields are:

@deftypevr {@code{files-configuration} parameter} log-location access-log
Defines the access log filename.  Specifying a blank filename disables
access log generation.  The value @code{stderr} causes log entries to be
sent to the standard error file when the scheduler is running in the
foreground, or to the system log daemon when run in the background.  The
value @code{syslog} causes log entries to be sent to the system log daemon.
The server name may be included in filenames using the string @code{%s}, as
in @code{/var/log/cups/%s-access_log}.

Defaults to @samp{"/var/log/cups/access_log"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name cache-dir
Where CUPS should cache data.

Defaults to @samp{"/var/cache/cups"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string config-file-perm
Specifies the permissions for all configuration files that the scheduler
writes.

Note that the permissions for the printers.conf file are currently masked to
only allow access from the scheduler user (typically root).  This is done
because printer device URIs sometimes contain sensitive authentication
information that should not be generally known on the system.  There is no
way to disable this security feature.

Defaults to @samp{"0640"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} log-location error-log
Defines the error log filename.  Specifying a blank filename disables access
log generation.  The value @code{stderr} causes log entries to be sent to
the standard error file when the scheduler is running in the foreground, or
to the system log daemon when run in the background.  The value
@code{syslog} causes log entries to be sent to the system log daemon.  The
server name may be included in filenames using the string @code{%s}, as in
@code{/var/log/cups/%s-error_log}.

Defaults to @samp{"/var/log/cups/error_log"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string fatal-errors
Specifies which errors are fatal, causing the scheduler to exit.  The kind
strings are:

@table @code
@item none
No errors are fatal.

@item all
All of the errors below are fatal.

@item browse
Browsing initialization errors are fatal, for example failed connections to
the DNS-SD daemon.

@item config
Configuration file syntax errors are fatal.

@item listen
Listen or Port errors are fatal, except for IPv6 failures on the loopback or
@code{any} addresses.

@item log
Log file creation or write errors are fatal.

@item permissions
Bad startup file permissions are fatal, for example shared TLS certificate
and key files with world-read permissions.
@end table

Defaults to @samp{"all -browse"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} boolean file-device?
Specifies whether the file pseudo-device can be used for new printer
queues.  The URI @uref{file:///dev/null} is always allowed.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string group
Specifies the group name or ID that will be used when executing external
programs.

Defaults to @samp{"lp"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string log-file-perm
Specifies the permissions for all log files that the scheduler writes.

Defaults to @samp{"0644"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} log-location page-log
Defines the page log filename.  Specifying a blank filename disables access
log generation.  The value @code{stderr} causes log entries to be sent to
the standard error file when the scheduler is running in the foreground, or
to the system log daemon when run in the background.  The value
@code{syslog} causes log entries to be sent to the system log daemon.  The
server name may be included in filenames using the string @code{%s}, as in
@code{/var/log/cups/%s-page_log}.

Defaults to @samp{"/var/log/cups/page_log"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string remote-root
Specifies the username that is associated with unauthenticated accesses by
clients claiming to be the root user.  The default is @code{remroot}.

Defaults to @samp{"remroot"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name request-root
Specifies the directory that contains print jobs and other HTTP request
data.

Defaults to @samp{"/var/spool/cups"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} sandboxing sandboxing
Specifies the level of security sandboxing that is applied to print filters,
backends, and other child processes of the scheduler; either @code{relaxed}
or @code{strict}.  This directive is currently only used/supported on macOS.

Defaults to @samp{strict}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name server-keychain
Specifies the location of TLS certificates and private keys.  CUPS will look
for public and private keys in this directory: a @code{.crt} files for
PEM-encoded certificates and corresponding @code{.key} files for PEM-encoded
private keys.

Defaults to @samp{"/etc/cups/ssl"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name server-root
Specifies the directory containing the server configuration files.

Defaults to @samp{"/etc/cups"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} boolean sync-on-close?
Specifies whether the scheduler calls fsync(2) after writing configuration
or state files.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} space-separated-string-list system-group
Specifies the group(s) to use for @code{@@SYSTEM} group authentication.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name temp-dir
Specifies the directory where temporary files are stored.

Defaults to @samp{"/var/spool/cups/tmp"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string user
Specifies the user name or ID that is used when running external programs.

Defaults to @samp{"lp"}.
@end deftypevr
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} access-log-level access-log-level
Specifies the logging level for the AccessLog file.  The @code{config} level
logs when printers and classes are added, deleted, or modified and when
configuration files are accessed or updated.  The @code{actions} level logs
when print jobs are submitted, held, released, modified, or canceled, and
any of the conditions for @code{config}.  The @code{all} level logs all
requests.

Defaults to @samp{actions}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean auto-purge-jobs?
Specifies whether to purge job history data automatically when it is no
longer required for quotas.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} browse-local-protocols browse-local-protocols
Specifies which protocols to use for local printer sharing.

Defaults to @samp{dnssd}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean browse-web-if?
Specifies whether the CUPS web interface is advertised.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean browsing?
Specifies whether shared printers are advertised.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string classification
Specifies the security classification of the server.  Any valid banner name
can be used, including "classified", "confidential", "secret", "topsecret",
and "unclassified", or the banner can be omitted to disable secure printing
functions.

Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean classify-override?
Specifies whether users may override the classification (cover page) of
individual print jobs using the @code{job-sheets} option.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} default-auth-type default-auth-type
Specifies the default type of authentication to use.

Defaults to @samp{Basic}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} default-encryption default-encryption
Specifies whether encryption will be used for authenticated requests.

Defaults to @samp{Required}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string default-language
Specifies the default language to use for text and web content.

Defaults to @samp{"en"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string default-paper-size
Specifies the default paper size for new print queues.  @samp{"Auto"} uses a
locale-specific default, while @samp{"None"} specifies there is no default
paper size.  Specific size names are typically @samp{"Letter"} or
@samp{"A4"}.

Defaults to @samp{"Auto"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string default-policy
Specifies the default access policy to use.

Defaults to @samp{"default"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean default-shared?
Specifies whether local printers are shared by default.

Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer dirty-clean-interval
Specifies the delay for updating of configuration and state files, in
seconds.  A value of 0 causes the update to happen as soon as possible,
typically within a few milliseconds.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} error-policy error-policy
Specifies what to do when an error occurs.  Possible values are
@code{abort-job}, which will discard the failed print job; @code{retry-job},
which will retry the job at a later time; @code{retry-this-job}, which
retries the failed job immediately; and @code{stop-printer}, which stops the
printer.

Defaults to @samp{stop-printer}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer filter-limit
Specifies the maximum cost of filters that are run concurrently, which can
be used to minimize disk, memory, and CPU resource problems.  A limit of 0
disables filter limiting.  An average print to a non-PostScript printer
needs a filter limit of about 200.  A PostScript printer needs about half
that (100).  Setting the limit below these thresholds will effectively limit
the scheduler to printing a single job at any time.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer filter-nice
Specifies the scheduling priority of filters that are run to print a job.
The nice value ranges from 0, the highest priority, to 19, the lowest
priority.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} host-name-lookups host-name-lookups
Specifies whether to do reverse lookups on connecting clients.  The
@code{double} setting causes @code{cupsd} to verify that the hostname
resolved from the address matches one of the addresses returned for that
hostname.  Double lookups also prevent clients with unregistered addresses
from connecting to your server.  Only set this option to @code{#t} or
@code{double} if absolutely required.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer job-kill-delay
Specifies the number of seconds to wait before killing the filters and
backend associated with a canceled or held job.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer job-retry-interval
Specifies the interval between retries of jobs in seconds.  This is
typically used for fax queues but can also be used with normal print queues
whose error policy is @code{retry-job} or @code{retry-current-job}.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer job-retry-limit
Specifies the number of retries that are done for jobs.  This is typically
used for fax queues but can also be used with normal print queues whose
error policy is @code{retry-job} or @code{retry-current-job}.

Defaults to @samp{5}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean keep-alive?
Specifies whether to support HTTP keep-alive connections.

Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer keep-alive-timeout
Specifies how long an idle client connection remains open, in seconds.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer limit-request-body
Specifies the maximum size of print files, IPP requests, and HTML form
data.  A limit of 0 disables the limit check.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} multiline-string-list listen
Listens on the specified interfaces for connections.  Valid values are of
the form @var{address}:@var{port}, where @var{address} is either an IPv6
address enclosed in brackets, an IPv4 address, or @code{*} to indicate all
addresses.  Values can also be file names of local UNIX domain sockets.  The
Listen directive is similar to the Port directive but allows you to restrict
access to specific interfaces or networks.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer listen-back-log
Specifies the number of pending connections that will be allowed.  This
normally only affects very busy servers that have reached the MaxClients
limit, but can also be triggered by large numbers of simultaneous
connections.  When the limit is reached, the operating system will refuse
additional connections until the scheduler can accept the pending ones.

Defaults to @samp{128}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} location-access-control-list location-access-controls
Specifies a set of additional access controls.

Available @code{location-access-controls} fields are:

@deftypevr {@code{location-access-controls} parameter} file-name path
Specifies the URI path to which the access control applies.
@end deftypevr

@deftypevr {@code{location-access-controls} parameter} access-control-list access-controls
Access controls for all access to this path, in the same format as the
@code{access-controls} of @code{operation-access-control}.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{location-access-controls} parameter} method-access-control-list method-access-controls
Access controls for method-specific access to this path.

Defaults to @samp{()}.

Available @code{method-access-controls} fields are:

@deftypevr {@code{method-access-controls} parameter} boolean reverse?
If @code{#t}, apply access controls to all methods except the listed
methods.  Otherwise apply to only the listed methods.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{method-access-controls} parameter} method-list methods
Methods to which this access control applies.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{method-access-controls} parameter} access-control-list access-controls
Access control directives, as a list of strings.  Each string should be one
directive, such as "Order allow,deny".

Defaults to @samp{()}.
@end deftypevr
@end deftypevr
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer log-debug-history
Specifies the number of debugging messages that are retained for logging if
an error occurs in a print job.  Debug messages are logged regardless of the
LogLevel setting.

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} log-level log-level
Specifies the level of logging for the ErrorLog file.  The value @code{none}
stops all logging while @code{debug2} logs everything.

Defaults to @samp{info}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} log-time-format log-time-format
Specifies the format of the date and time in the log files.  The value
@code{standard} logs whole seconds while @code{usecs} logs microseconds.

Defaults to @samp{standard}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-clients
Specifies the maximum number of simultaneous clients that are allowed by the
scheduler.

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-clients-per-host
Specifies the maximum number of simultaneous clients that are allowed from a
single address.

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-copies
Specifies the maximum number of copies that a user can print of each job.

Defaults to @samp{9999}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-hold-time
Specifies the maximum time a job may remain in the @code{indefinite} hold
state before it is canceled.  A value of 0 disables cancellation of held
jobs.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-jobs
Specifies the maximum number of simultaneous jobs that are allowed.  Set to
0 to allow an unlimited number of jobs.

Defaults to @samp{500}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-jobs-per-printer
Specifies the maximum number of simultaneous jobs that are allowed per
printer.  A value of 0 allows up to MaxJobs jobs per printer.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-jobs-per-user
Specifies the maximum number of simultaneous jobs that are allowed per
user.  A value of 0 allows up to MaxJobs jobs per user.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-job-time
Specifies the maximum time a job may take to print before it is canceled, in
seconds.  Set to 0 to disable cancellation of "stuck" jobs.

Defaults to @samp{10800}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-log-size
Specifies the maximum size of the log files before they are rotated, in
bytes.  The value 0 disables log rotation.

Defaults to @samp{1048576}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer multiple-operation-timeout
Specifies the maximum amount of time to allow between files in a multiple
file print job, in seconds.

Defaults to @samp{300}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string page-log-format
Specifies the format of PageLog lines.  Sequences beginning with percent
(@samp{%}) characters are replaced with the corresponding information, while
all other characters are copied literally.  The following percent sequences
are recognized:

@table @samp
@item %%
insert a single percent character

@item %@{name@}
insert the value of the specified IPP attribute

@item %C
insert the number of copies for the current page

@item %P
insert the current page number

@item %T
insert the current date and time in common log format

@item %j
insert the job ID

@item %p
insert the printer name

@item %u
insert the username
@end table

A value of the empty string disables page logging.  The string @code{%p %u
%j %T %P %C %@{job-billing@} %@{job-originating-host-name@} %@{job-name@}
%@{media@} %@{sides@}} creates a page log with the standard items.

Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} environment-variables environment-variables
Passes the specified environment variable(s) to child processes; a list of
strings.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} policy-configuration-list policies
Specifies named access control policies.

Available @code{policy-configuration} fields are:

@deftypevr {@code{policy-configuration} parameter} string name
Name of the policy.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string job-private-access
Specifies an access list for a job's private values.  @code{@@ACL} maps to
the printer's requesting-user-name-allowed or requesting-user-name-denied
values.  @code{@@OWNER} maps to the job's owner.  @code{@@SYSTEM} maps to
the groups listed for the @code{system-group} field of the
@code{files-config} configuration, which is reified into the
@code{cups-files.conf(5)} file.  Other possible elements of the access list
include specific user names, and @code{@@@var{group}} to indicate members of
a specific group.  The access list may also be simply @code{all} or
@code{default}.

Defaults to @samp{"@@OWNER @@SYSTEM"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string job-private-values
Specifies the list of job values to make private, or @code{all},
@code{default}, or @code{none}.

Defaults to @samp{"job-name job-originating-host-name
job-originating-user-name phone"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string subscription-private-access
Specifies an access list for a subscription's private values.  @code{@@ACL}
maps to the printer's requesting-user-name-allowed or
requesting-user-name-denied values.  @code{@@OWNER} maps to the job's
owner.  @code{@@SYSTEM} maps to the groups listed for the
@code{system-group} field of the @code{files-config} configuration, which is
reified into the @code{cups-files.conf(5)} file.  Other possible elements of
the access list include specific user names, and @code{@@@var{group}} to
indicate members of a specific group.  The access list may also be simply
@code{all} or @code{default}.

Defaults to @samp{"@@OWNER @@SYSTEM"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string subscription-private-values
Specifies the list of job values to make private, or @code{all},
@code{default}, or @code{none}.

Defaults to @samp{"notify-events notify-pull-method notify-recipient-uri
notify-subscriber-user-name notify-user-data"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} operation-access-control-list access-controls
Access control by IPP operation.

Defaults to @samp{()}.
@end deftypevr
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean-or-non-negative-integer preserve-job-files
Specifies whether job files (documents) are preserved after a job is
printed.  If a numeric value is specified, job files are preserved for the
indicated number of seconds after printing.  Otherwise a boolean value
applies indefinitely.

Defaults to @samp{86400}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean-or-non-negative-integer preserve-job-history
Specifies whether the job history is preserved after a job is printed.  If a
numeric value is specified, the job history is preserved for the indicated
number of seconds after printing.  If @code{#t}, the job history is
preserved until the MaxJobs limit is reached.

Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer reload-timeout
Specifies the amount of time to wait for job completion before restarting
the scheduler.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string rip-cache
Specifies the maximum amount of memory to use when converting documents into
bitmaps for a printer.

Defaults to @samp{"128m"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string server-admin
Specifies the email address of the server administrator.

Defaults to @samp{"root@@localhost.localdomain"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} host-name-list-or-* server-alias
The ServerAlias directive is used for HTTP Host header validation when
clients connect to the scheduler from external interfaces.  Using the
special name @code{*} can expose your system to known browser-based DNS
rebinding attacks, even when accessing sites through a firewall.  If the
auto-discovery of alternate names does not work, we recommend listing each
alternate name with a ServerAlias directive instead of using @code{*}.

Defaults to @samp{*}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string server-name
Specifies the fully-qualified host name of the server.

Defaults to @samp{"localhost"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} server-tokens server-tokens
Specifies what information is included in the Server header of HTTP
responses.  @code{None} disables the Server header.  @code{ProductOnly}
reports @code{CUPS}.  @code{Major} reports @code{CUPS 2}.  @code{Minor}
reports @code{CUPS 2.0}.  @code{Minimal} reports @code{CUPS 2.0.0}.
@code{OS} reports @code{CUPS 2.0.0 (@var{uname})} where @var{uname} is the
output of the @code{uname} command.  @code{Full} reports @code{CUPS 2.0.0
(@var{uname}) IPP/2.0}.

Defaults to @samp{Minimal}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string set-env
Set the specified environment variable to be passed to child processes.

Defaults to @samp{"variable value"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} multiline-string-list ssl-listen
Listens on the specified interfaces for encrypted connections.  Valid values
are of the form @var{address}:@var{port}, where @var{address} is either an
IPv6 address enclosed in brackets, an IPv4 address, or @code{*} to indicate
all addresses.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} ssl-options ssl-options
Sets encryption options.  By default, CUPS only supports encryption using
TLS v1.0 or higher using known secure cipher suites.  The @code{AllowRC4}
option enables the 128-bit RC4 cipher suites, which are required for some
older clients that do not implement newer ones.  The @code{AllowSSL3} option
enables SSL v3.0, which is required for some older clients that do not
support TLS v1.0.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean strict-conformance?
Specifies whether the scheduler requires clients to strictly adhere to the
IPP specifications.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer timeout
Specifies the HTTP request timeout, in seconds.

Defaults to @samp{300}.

@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean web-interface?
Specifies whether the web interface is enabled.

Defaults to @samp{#f}.
@end deftypevr

At this point you're probably thinking ``oh dear, Guix manual, I like you
but you can stop already with the configuration options''.  Indeed.
However, one more point: it could be that you have an existing
@code{cupsd.conf} that you want to use.  In that case, you can pass an
@code{opaque-cups-configuration} as the configuration of a
@code{cups-service-type}.

Available @code{opaque-cups-configuration} fields are:

@deftypevr {@code{opaque-cups-configuration} parameter} package cups
The CUPS package.
@end deftypevr

@deftypevr {@code{opaque-cups-configuration} parameter} string cupsd.conf
The contents of the @code{cupsd.conf}, as a string.
@end deftypevr

@deftypevr {@code{opaque-cups-configuration} parameter} string cups-files.conf
The contents of the @code{cups-files.conf} file, as a string.
@end deftypevr

For example, if your @code{cupsd.conf} and @code{cups-files.conf} are in
strings of the same name, you could instantiate a CUPS service like this:

@example
(service cups-service-type
         (opaque-cups-configuration
           (cupsd.conf cupsd.conf)
           (cups-files.conf cups-files.conf)))
@end example


@node Desktop-Dienste
@subsubsection Desktop-Dienste

The @code{(gnu services desktop)} module provides services that are usually
useful in the context of a ``desktop'' setup---that is, on a machine running
a graphical display server, possibly with graphical user interfaces, etc.
It also defines services that provide specific desktop environments like
GNOME, XFCE or MATE.

To simplify things, the module defines a variable containing the set of
services that users typically expect on a machine with a graphical
environment and networking:

@defvr {Scheme Variable} %desktop-services
This is a list of services that builds upon @var{%base-services} and adds or
adjusts services for a typical ``desktop'' setup.

In particular, it adds a graphical login manager (@pxref{X Window,
@code{slim-service}}), screen lockers, a network management tool
(@pxref{Netzwerkdienste, @code{network-manager-service-type}}), energy
and color management services, the @code{elogind} login and seat manager,
the Polkit privilege service, the GeoClue location service, the
AccountsService daemon that allows authorized users change system passwords,
an NTP client (@pxref{Netzwerkdienste}), the Avahi daemon, and has the
name service switch service configured to be able to use @code{nss-mdns}
(@pxref{Name Service Switch, mDNS}).
@end defvr

The @var{%desktop-services} variable can be used as the @code{services}
field of an @code{operating-system} declaration (@pxref{„operating-system“-Referenz, @code{services}}).

Additionally, the @code{gnome-desktop-service}, @code{xfce-desktop-service},
@code{mate-desktop-service} and @code{enlightenment-desktop-service-type}
procedures can add GNOME, XFCE, MATE and/or Enlightenment to a system.  To
``add GNOME'' means that system-level services like the backlight adjustment
helpers and the power management utilities are added to the system,
extending @code{polkit} and @code{dbus} appropriately, allowing GNOME to
operate with elevated privileges on a limited number of special-purpose
system interfaces.  Additionally, adding a service made by
@code{gnome-desktop-service} adds the GNOME metapackage to the system
profile.  Likewise, adding the XFCE service not only adds the @code{xfce}
metapackage to the system profile, but it also gives the Thunar file manager
the ability to open a ``root-mode'' file management window, if the user
authenticates using the administrator's password via the standard polkit
graphical interface.  To ``add MATE'' means that @code{polkit} and
@code{dbus} are extended appropriately, allowing MATE to operate with
elevated privileges on a limited number of special-purpose system
interfaces.  Additionally, adding a service made by
@code{mate-desktop-service} adds the MATE metapackage to the system
profile.  ``Adding ENLIGHTENMENT'' means that @code{dbus} is extended
appropriately, and several of Enlightenment's binaries are set as setuid,
allowing Enlightenment's screen locker and other functionality to work as
expetected.

The desktop environments in Guix use the Xorg display server by default.  If
you'd like to use the newer display server protocol called Wayland, you need
to use the @code{sddm-service} instead of the @code{slim-service} for the
graphical login manager.  You should then select the ``GNOME (Wayland)''
session in SDDM.  Alternatively you can also try starting GNOME on Wayland
manually from a TTY with the command ``XDG_SESSION_TYPE=wayland exec
dbus-run-session gnome-session``.  Currently only GNOME has support for
Wayland.

@deffn {Scheme Procedure} gnome-desktop-service
Return a service that adds the @code{gnome} package to the system profile,
and extends polkit with the actions from @code{gnome-settings-daemon}.
@end deffn

@deffn {Scheme Procedure} xfce-desktop-service
Return a service that adds the @code{xfce} package to the system profile,
and extends polkit with the ability for @code{thunar} to manipulate the file
system as root from within a user session, after the user has authenticated
with the administrator's password.
@end deffn

@deffn {Scheme Procedure} mate-desktop-service
Return a service that adds the @code{mate} package to the system profile,
and extends polkit with the actions from @code{mate-settings-daemon}.
@end deffn

@deffn {Scheme Procedure} enlightenment-desktop-service-type
Return a service that adds the @code{enlightenment} package to the system
profile, and extends dbus with actions from @code{efl}.
@end deffn

@deftp {Data Type} enlightenment-desktop-service-configuration
@table @asis
@item @code{enlightenment} (default @code{enlightenment})
The enlightenment package to use.
@end table
@end deftp

Because the GNOME, XFCE and MATE desktop services pull in so many packages,
the default @code{%desktop-services} variable doesn't include any of them by
default.  To add GNOME, XFCE or MATE, just @code{cons} them onto
@code{%desktop-services} in the @code{services} field of your
@code{operating-system}:

@example
(use-modules (gnu))
(use-service-modules desktop)
(operating-system
  ...
  ;; cons* adds items to the list given as its last argument.
  (services (cons* (gnome-desktop-service)
                   (xfce-desktop-service)
                   %desktop-services))
  ...)
@end example

These desktop environments will then be available as options in the
graphical login window.

The actual service definitions included in @code{%desktop-services} and
provided by @code{(gnu services dbus)} and @code{(gnu services desktop)} are
described below.

@deffn {Scheme Procedure} dbus-service [#:dbus @var{dbus}] [#:services '()]
Return a service that runs the ``system bus'', using @var{dbus}, with
support for @var{services}.

@uref{http://dbus.freedesktop.org/, D-Bus} is an inter-process communication
facility.  Its system bus is used to allow system services to communicate
and to be notified of system-wide events.

@var{services} must be a list of packages that provide an
@file{etc/dbus-1/system.d} directory containing additional D-Bus
configuration and policy files.  For example, to allow avahi-daemon to use
the system bus, @var{services} must be equal to @code{(list avahi)}.
@end deffn

@deffn {Scheme Procedure} elogind-service [#:config @var{config}]
Return a service that runs the @code{elogind} login and seat management
daemon.  @uref{https://github.com/elogind/elogind, Elogind} exposes a D-Bus
interface that can be used to know which users are logged in, know what kind
of sessions they have open, suspend the system, inhibit system suspend,
reboot the system, and other tasks.

Elogind handles most system-level power events for a computer, for example
suspending the system when a lid is closed, or shutting it down when the
power button is pressed.

The @var{config} keyword argument specifies the configuration for elogind,
and should be the result of an @code{(elogind-configuration (@var{parameter}
@var{value})...)} invocation.  Available parameters and their default values
are:

@table @code
@item kill-user-processes?
@code{#f}
@item kill-only-users
@code{()}
@item kill-exclude-users
@code{("root")}
@item inhibit-delay-max-seconds
@code{5}
@item handle-power-key
@code{poweroff}
@item handle-suspend-key
@code{suspend}
@item handle-hibernate-key
@code{hibernate}
@item handle-lid-switch
@code{suspend}
@item handle-lid-switch-docked
@code{ignore}
@item power-key-ignore-inhibited?
@code{#f}
@item suspend-key-ignore-inhibited?
@code{#f}
@item hibernate-key-ignore-inhibited?
@code{#f}
@item lid-switch-ignore-inhibited?
@code{#t}
@item holdoff-timeout-seconds
@code{30}
@item idle-action
@code{ignore}
@item idle-action-seconds
@code{(* 30 60)}
@item runtime-directory-size-percent
@code{10}
@item runtime-directory-size
@code{#f}
@item remove-ipc?
@code{#t}
@item suspend-state
@code{("mem" "standby" "freeze")}
@item suspend-mode
@code{()}
@item hibernate-state
@code{("disk")}
@item hibernate-mode
@code{("platform" "shutdown")}
@item hybrid-sleep-state
@code{("disk")}
@item hybrid-sleep-mode
@code{("suspend" "platform" "shutdown")}
@end table
@end deffn

@deffn {Scheme Procedure} accountsservice-service @
       [#:accountsservice @var{accountsservice}] Return a service that runs
AccountsService, a system service that can list available accounts, change
their passwords, and so on.  AccountsService integrates with PolicyKit to
enable unprivileged users to acquire the capability to modify their system
configuration.
@uref{https://www.freedesktop.org/wiki/Software/AccountsService/, the
accountsservice web site} for more information.

The @var{accountsservice} keyword argument is the @code{accountsservice}
package to expose as a service.
@end deffn

@deffn {Scheme Procedure} polkit-service @
                         [#:polkit @var{polkit}] Return a service that runs the
@uref{http://www.freedesktop.org/wiki/Software/polkit/, Polkit privilege
management service}, which allows system administrators to grant access to
privileged operations in a structured way.  By querying the Polkit service,
a privileged system component can know when it should grant additional
capabilities to ordinary users.  For example, an ordinary user can be
granted the capability to suspend the system if the user is logged in
locally.
@end deffn

@deffn {Scheme Procedure} upower-service [#:upower @var{upower}] @
                         [#:watts-up-pro? #f] @ [#:poll-batteries? #t] @ [#:ignore-lid? #f] @
[#:use-percentage-for-policy? #f] @ [#:percentage-low 10] @
[#:percentage-critical 3] @ [#:percentage-action 2] @ [#:time-low 1200] @
[#:time-critical 300] @ [#:time-action 120] @ [#:critical-power-action
'hybrid-sleep] Return a service that runs
@uref{http://upower.freedesktop.org/, @command{upowerd}}, a system-wide
monitor for power consumption and battery levels, with the given
configuration settings.  It implements the @code{org.freedesktop.UPower}
D-Bus interface, and is notably used by GNOME.
@end deffn

@deffn {Scheme Procedure} udisks-service [#:udisks @var{udisks}]
Return a service for @uref{http://udisks.freedesktop.org/docs/latest/,
UDisks}, a @dfn{disk management} daemon that provides user interfaces with
notifications and ways to mount/unmount disks.  Programs that talk to UDisks
include the @command{udisksctl} command, part of UDisks, and GNOME Disks.
@end deffn

@deffn {Scheme Procedure} colord-service [#:colord @var{colord}]
Return a service that runs @command{colord}, a system service with a D-Bus
interface to manage the color profiles of input and output devices such as
screens and scanners.  It is notably used by the GNOME Color Manager
graphical tool.  See @uref{http://www.freedesktop.org/software/colord/, the
colord web site} for more information.
@end deffn

@deffn {Scheme Procedure} geoclue-application name [#:allowed? #t] [#:system? #f] [#:users '()]
Return a configuration allowing an application to access GeoClue location
data.  @var{name} is the Desktop ID of the application, without the
@code{.desktop} part.  If @var{allowed?} is true, the application will have
access to location information by default.  The boolean @var{system?} value
indicates whether an application is a system component or not.  Finally
@var{users} is a list of UIDs of all users for which this application is
allowed location info access.  An empty users list means that all users are
allowed.
@end deffn

@defvr {Scheme Variable} %standard-geoclue-applications
The standard list of well-known GeoClue application configurations, granting
authority to the GNOME date-and-time utility to ask for the current location
in order to set the time zone, and allowing the IceCat and Epiphany web
browsers to request location information.  IceCat and Epiphany both query
the user before allowing a web page to know the user's location.
@end defvr

@deffn {Scheme Procedure} geoclue-service [#:colord @var{colord}] @
                         [#:whitelist '()] @ [#:wifi-geolocation-url
"https://location.services.mozilla.com/v1/geolocate?key=geoclue"] @
[#:submit-data? #f] [#:wifi-submission-url
"https://location.services.mozilla.com/v1/submit?key=geoclue"] @
[#:submission-nick "geoclue"] @ [#:applications
%standard-geoclue-applications] Return a service that runs the GeoClue
location service.  This service provides a D-Bus interface to allow
applications to request access to a user's physical location, and optionally
to add information to online location databases.  See
@uref{https://wiki.freedesktop.org/www/Software/GeoClue/, the GeoClue web
site} for more information.
@end deffn

@deffn {Scheme Procedure} bluetooth-service [#:bluez @var{bluez}] @
       [@w{#:auto-enable? #f}] Return a service that runs the @command{bluetoothd}
daemon, which manages all the Bluetooth devices and provides a number of
D-Bus interfaces.  When AUTO-ENABLE? is true, the bluetooth controller is
powered automatically at boot, which can be useful when using a bluetooth
keyboard or mouse.

Users need to be in the @code{lp} group to access the D-Bus service.
@end deffn

@node Tondienste
@subsubsection Tondienste

@cindex sound support
@cindex ALSA
@cindex PulseAudio, sound support

The @code{(gnu services sound)} module provides a service to configure the
Advanced Linux Sound Architecture (ALSA) system, which making PulseAudio the
preferred ALSA output driver.

@deffn {Scheme Variable} alsa-service-type
This is the type for the @uref{https://alsa-project.org/, Advanced Linux
Sound Architecture} (ALSA) system, which generates the
@file{/etc/asound.conf} configuration file.  The value for this type is a
@command{alsa-configuration} record as in this example:

@example
(service alsa-service-type)
@end example

See below for details about @code{alsa-configuration}.
@end deffn

@deftp {Data Type} alsa-configuration
Data type representing the configuration for @code{alsa-service}.

@table @asis
@item @code{alsa-plugins} (default: @var{alsa-plugins})
@code{alsa-plugins} package to use.

@item @code{pulseaudio?} (default: @var{#t})
Whether ALSA applications should transparently be made to use the
@uref{http://www.pulseaudio.org/, PulseAudio} sound server.

Using PulseAudio allows you to run several sound-producing applications at
the same time and to individual control them @i{via} @command{pavucontrol},
among other things.

@item @code{extra-options} (default: @var{""})
String to append to the @file{/etc/asound.conf} file.

@end table
@end deftp

Individual users who want to override the system configuration of ALSA can
do it with the @file{~/.asoundrc} file:

@example
# In guix, we have to specify the absolute path for plugins.
pcm_type.jack @{
  lib "/home/alice/.guix-profile/lib/alsa-lib/libasound_module_pcm_jack.so"
@}

# Routing ALSA to jack:
# <http://jackaudio.org/faq/routing_alsa.html>.
pcm.rawjack @{
  type jack
  playback_ports @{
    0 system:playback_1
    1 system:playback_2
  @}

  capture_ports @{
    0 system:capture_1
    1 system:capture_2
  @}
@}

pcm.!default @{
  type plug
  slave @{
    pcm "rawjack"
  @}
@}
@end example

See @uref{https://www.alsa-project.org/main/index.php/Asoundrc} for the
details.


@node Datenbankdienste
@subsubsection Datenbankdienste

@cindex database
@cindex SQL
The @code{(gnu services databases)} module provides the following services.

@deffn {Scheme Procedure} postgresql-service [#:postgresql postgresql] @
       [#:config-file] [#:data-directory ``/var/lib/postgresql/data''] @ [#:port
5432] [#:locale ``en_US.utf8''] Return a service that runs @var{postgresql},
the PostgreSQL database server.

The PostgreSQL daemon loads its runtime configuration from
@var{config-file}, creates a database cluster with @var{locale} as the
default locale, stored in @var{data-directory}.  It then listens on
@var{port}.
@end deffn

@deffn {Scheme Procedure} mysql-service [#:config (mysql-configuration)]
Return a service that runs @command{mysqld}, the MySQL or MariaDB database
server.

The optional @var{config} argument specifies the configuration for
@command{mysqld}, which should be a @code{<mysql-configuration>} object.
@end deffn

@deftp {Data Type} mysql-configuration
Data type representing the configuration of @var{mysql-service}.

@table @asis
@item @code{mysql} (default: @var{mariadb})
Package object of the MySQL database server, can be either @var{mariadb} or
@var{mysql}.

For MySQL, a temporary root password will be displayed at activation time.
For MariaDB, the root password is empty.

@item @code{port} (default: @code{3306})
TCP port on which the database server listens for incoming connections.
@end table
@end deftp

@defvr {Scheme Variable} memcached-service-type
This is the service type for the @uref{https://memcached.org/, Memcached}
service, which provides a distributed in memory cache.  The value for the
service type is a @code{memcached-configuration} object.
@end defvr

@example
(service memcached-service-type)
@end example

@deftp {Data Type} memcached-configuration
Data type representing the configuration of memcached.

@table @asis
@item @code{memcached} (default: @code{memcached})
The Memcached package to use.

@item @code{interfaces} (default: @code{'("0.0.0.0")})
Network interfaces on which to listen.

@item @code{tcp-port} (default: @code{11211})
Port on which to accept connections on,

@item @code{udp-port} (default: @code{11211})
Port on which to accept UDP connections on, a value of 0 will disable
listening on a UDP socket.

@item @code{additional-options} (default: @code{'()})
Additional command line options to pass to @code{memcached}.
@end table
@end deftp

@defvr {Scheme Variable} mongodb-service-type
This is the service type for @uref{https://www.mongodb.com/, MongoDB}.  The
value for the service type is a @code{mongodb-configuration} object.
@end defvr

@example
(service mongodb-service-type)
@end example

@deftp {Data Type} mongodb-configuration
Data type representing the configuration of mongodb.

@table @asis
@item @code{mongodb} (default: @code{mongodb})
The MongoDB package to use.

@item @code{config-file} (default: @code{%default-mongodb-configuration-file})
The configuration file for MongoDB.

@item @code{data-directory} (default: @code{"/var/lib/mongodb"})
This value is used to create the directory, so that it exists and is owned
by the mongodb user.  It should match the data-directory which MongoDB is
configured to use through the configuration file.
@end table
@end deftp

@defvr {Scheme Variable} redis-service-type
This is the service type for the @uref{https://redis.io/, Redis} key/value
store, whose value is a @code{redis-configuration} object.
@end defvr

@deftp {Data Type} redis-configuration
Data type representing the configuration of redis.

@table @asis
@item @code{redis} (default: @code{redis})
The Redis package to use.

@item @code{bind} (default: @code{"127.0.0.1"})
Network interface on which to listen.

@item @code{port} (default: @code{6379})
Port on which to accept connections on, a value of 0 will disable listening
on a TCP socket.

@item @code{working-directory} (default: @code{"/var/lib/redis"})
Directory in which to store the database and related files.
@end table
@end deftp

@node Mail-Dienste
@subsubsection Mail-Dienste

@cindex mail
@cindex email
The @code{(gnu services mail)} module provides Guix service definitions for
email services: IMAP, POP3, and LMTP servers, as well as mail transport
agents (MTAs).  Lots of acronyms! These services are detailed in the
subsections below.

@subsubheading Dovecot Service

@deffn {Scheme Procedure} dovecot-service [#:config (dovecot-configuration)]
Return a service that runs the Dovecot IMAP/POP3/LMTP mail server.
@end deffn

By default, Dovecot does not need much configuration; the default
configuration object created by @code{(dovecot-configuration)} will suffice
if your mail is delivered to @code{~/Maildir}.  A self-signed certificate
will be generated for TLS-protected connections, though Dovecot will also
listen on cleartext ports by default.  There are a number of options,
though, which mail administrators might need to change, and as is the case
with other services, Guix allows the system administrator to specify these
parameters via a uniform Scheme interface.

For example, to specify that mail is located at @code{maildir~/.mail}, one
would instantiate the Dovecot service like this:

@example
(dovecot-service #:config
                 (dovecot-configuration
                  (mail-location "maildir:~/.mail")))
@end example

The available configuration parameters follow.  Each parameter definition is
preceded by its type; for example, @samp{string-list foo} indicates that the
@code{foo} parameter should be specified as a list of strings.  There is
also a way to specify the configuration as a string, if you have an old
@code{dovecot.conf} file that you want to port over from some other system;
see the end for more details.

@c The following documentation was initially generated by
@c (generate-documentation) in (gnu services mail).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as dovecot updates.

Available @code{dovecot-configuration} fields are:

@deftypevr {@code{dovecot-configuration} parameter} package dovecot
The dovecot package.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} comma-separated-string-list listen
A list of IPs or hosts where to listen for connections.  @samp{*} listens on
all IPv4 interfaces, @samp{::} listens on all IPv6 interfaces.  If you want
to specify non-default ports or anything more complex, customize the address
and port fields of the @samp{inet-listener} of the specific services you are
interested in.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} protocol-configuration-list protocols
List of protocols we want to serve.  Available protocols include
@samp{imap}, @samp{pop3}, and @samp{lmtp}.

Available @code{protocol-configuration} fields are:

@deftypevr {@code{protocol-configuration} parameter} string name
The name of the protocol.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} string auth-socket-path
UNIX socket path to the master authentication server to find users.  This is
used by imap (for shared users) and lda.  It defaults to
@samp{"/var/run/dovecot/auth-userdb"}.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} space-separated-string-list mail-plugins
Space separated list of plugins to load.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} non-negative-integer mail-max-userip-connections
Maximum number of IMAP connections allowed for a user from each IP address.
NOTE: The username is compared case-sensitively.  Defaults to @samp{10}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} service-configuration-list services
List of services to enable.  Available services include @samp{imap},
@samp{imap-login}, @samp{pop3}, @samp{pop3-login}, @samp{auth}, and
@samp{lmtp}.

Available @code{service-configuration} fields are:

@deftypevr {@code{service-configuration} parameter} string kind
The service kind.  Valid values include @code{director}, @code{imap-login},
@code{pop3-login}, @code{lmtp}, @code{imap}, @code{pop3}, @code{auth},
@code{auth-worker}, @code{dict}, @code{tcpwrap}, @code{quota-warning}, or
anything else.
@end deftypevr

@deftypevr {@code{service-configuration} parameter} listener-configuration-list listeners
Listeners for the service.  A listener is either a
@code{unix-listener-configuration}, a @code{fifo-listener-configuration}, or
an @code{inet-listener-configuration}.  Defaults to @samp{()}.

Available @code{unix-listener-configuration} fields are:

@deftypevr {@code{unix-listener-configuration} parameter} string path
Path to the file, relative to @code{base-dir} field.  This is also used as
the section name.
@end deftypevr

@deftypevr {@code{unix-listener-configuration} parameter} string mode
The access mode for the socket.  Defaults to @samp{"0600"}.
@end deftypevr

@deftypevr {@code{unix-listener-configuration} parameter} string user
The user to own the socket.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{unix-listener-configuration} parameter} string group
The group to own the socket.  Defaults to @samp{""}.
@end deftypevr


Available @code{fifo-listener-configuration} fields are:

@deftypevr {@code{fifo-listener-configuration} parameter} string path
Path to the file, relative to @code{base-dir} field.  This is also used as
the section name.
@end deftypevr

@deftypevr {@code{fifo-listener-configuration} parameter} string mode
The access mode for the socket.  Defaults to @samp{"0600"}.
@end deftypevr

@deftypevr {@code{fifo-listener-configuration} parameter} string user
The user to own the socket.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{fifo-listener-configuration} parameter} string group
The group to own the socket.  Defaults to @samp{""}.
@end deftypevr


Available @code{inet-listener-configuration} fields are:

@deftypevr {@code{inet-listener-configuration} parameter} string protocol
The protocol to listen for.
@end deftypevr

@deftypevr {@code{inet-listener-configuration} parameter} string address
The address on which to listen, or empty for all addresses.  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{inet-listener-configuration} parameter} non-negative-integer port
The port on which to listen.
@end deftypevr

@deftypevr {@code{inet-listener-configuration} parameter} boolean ssl?
Whether to use SSL for this service; @samp{yes}, @samp{no}, or
@samp{required}.  Defaults to @samp{#t}.
@end deftypevr

@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer service-count
Number of connections to handle before starting a new process.  Typically
the only useful values are 0 (unlimited) or 1.  1 is more secure, but 0 is
faster.  <doc/wiki/LoginProcess.txt>.  Defaults to @samp{1}.
@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer process-min-avail
Number of processes to always keep waiting for more connections.  Defaults
to @samp{0}.
@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer vsz-limit
If you set @samp{service-count 0}, you probably need to grow this.  Defaults
to @samp{256000000}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} dict-configuration dict
Dict configuration, as created by the @code{dict-configuration} constructor.

Available @code{dict-configuration} fields are:

@deftypevr {@code{dict-configuration} parameter} free-form-fields entries
A list of key-value pairs that this dict should hold.  Defaults to
@samp{()}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} passdb-configuration-list passdbs
A list of passdb configurations, each one created by the
@code{passdb-configuration} constructor.

Available @code{passdb-configuration} fields are:

@deftypevr {@code{passdb-configuration} parameter} string driver
The driver that the passdb should use.  Valid values include @samp{pam},
@samp{passwd}, @samp{shadow}, @samp{bsdauth}, and @samp{static}.  Defaults
to @samp{"pam"}.
@end deftypevr

@deftypevr {@code{passdb-configuration} parameter} space-separated-string-list args
Space separated list of arguments to the passdb driver.  Defaults to
@samp{""}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} userdb-configuration-list userdbs
List of userdb configurations, each one created by the
@code{userdb-configuration} constructor.

Available @code{userdb-configuration} fields are:

@deftypevr {@code{userdb-configuration} parameter} string driver
The driver that the userdb should use.  Valid values include @samp{passwd}
and @samp{static}.  Defaults to @samp{"passwd"}.
@end deftypevr

@deftypevr {@code{userdb-configuration} parameter} space-separated-string-list args
Space separated list of arguments to the userdb driver.  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{userdb-configuration} parameter} free-form-args override-fields
Override fields from passwd.  Defaults to @samp{()}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} plugin-configuration plugin-configuration
Plug-in configuration, created by the @code{plugin-configuration}
constructor.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} list-of-namespace-configuration namespaces
List of namespaces.  Each item in the list is created by the
@code{namespace-configuration} constructor.

Available @code{namespace-configuration} fields are:

@deftypevr {@code{namespace-configuration} parameter} string name
Name for this namespace.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string type
Namespace type: @samp{private}, @samp{shared} or @samp{public}.  Defaults to
@samp{"private"}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string separator
Hierarchy separator to use. You should use the same separator for all
namespaces or some clients get confused.  @samp{/} is usually a good one.
The default however depends on the underlying mail storage format.  Defaults
to @samp{""}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string prefix
Prefix required to access this namespace.  This needs to be different for
all namespaces. For example @samp{Public/}.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string location
Physical location of the mailbox. This is in the same format as
mail_location, which is also the default for it.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean inbox?
There can be only one INBOX, and this setting defines which namespace has
it.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean hidden?
If namespace is hidden, it's not advertised to clients via NAMESPACE
extension. You'll most likely also want to set @samp{list? #f}.  This is
mostly useful when converting from another server with different namespaces
which you want to deprecate but still keep working.  For example you can
create hidden namespaces with prefixes @samp{~/mail/}, @samp{~%u/mail/} and
@samp{mail/}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean list?
Show the mailboxes under this namespace with the LIST command. This makes
the namespace visible for clients that do not support the NAMESPACE
extension.  The special @code{children} value lists child mailboxes, but
hides the namespace prefix.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean subscriptions?
Namespace handles its own subscriptions.  If set to @code{#f}, the parent
namespace handles them.  The empty prefix should always have this as
@code{#t}).  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} mailbox-configuration-list mailboxes
List of predefined mailboxes in this namespace.  Defaults to @samp{()}.

Available @code{mailbox-configuration} fields are:

@deftypevr {@code{mailbox-configuration} parameter} string name
Name for this mailbox.
@end deftypevr

@deftypevr {@code{mailbox-configuration} parameter} string auto
@samp{create} will automatically create this mailbox.  @samp{subscribe} will
both create and subscribe to the mailbox.  Defaults to @samp{"no"}.
@end deftypevr

@deftypevr {@code{mailbox-configuration} parameter} space-separated-string-list special-use
List of IMAP @code{SPECIAL-USE} attributes as specified by RFC 6154.  Valid
values are @code{\All}, @code{\Archive}, @code{\Drafts}, @code{\Flagged},
@code{\Junk}, @code{\Sent}, and @code{\Trash}.  Defaults to @samp{()}.
@end deftypevr

@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name base-dir
Base directory where to store runtime data.  Defaults to
@samp{"/var/run/dovecot/"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string login-greeting
Greeting message for clients.  Defaults to @samp{"Dovecot ready."}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list login-trusted-networks
List of trusted network ranges.  Connections from these IPs are allowed to
override their IP addresses and ports (for logging and for authentication
checks).  @samp{disable-plaintext-auth} is also ignored for these networks.
Typically you would specify your IMAP proxy servers here.  Defaults to
@samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list login-access-sockets
List of login access check sockets (e.g. tcpwrap).  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean verbose-proctitle?
Show more verbose process titles (in ps).  Currently shows user name and IP
address.  Useful for seeing who is actually using the IMAP processes
(e.g. shared mailboxes or if the same uid is used for multiple accounts).
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean shutdown-clients?
Should all processes be killed when Dovecot master process shuts down.
Setting this to @code{#f} means that Dovecot can be upgraded without forcing
existing client connections to close (although that could also be a problem
if the upgrade is e.g. due to a security fix).  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer doveadm-worker-count
If non-zero, run mail commands via this many connections to doveadm server,
instead of running them directly in the same process.  Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string doveadm-socket-path
UNIX socket or host:port used for connecting to doveadm server.  Defaults to
@samp{"doveadm-server"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list import-environment
List of environment variables that are preserved on Dovecot startup and
passed down to all of its child processes.  You can also give key=value
pairs to always set specific settings.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean disable-plaintext-auth?
Disable LOGIN command and all other plaintext authentications unless SSL/TLS
is used (LOGINDISABLED capability).  Note that if the remote IP matches the
local IP (i.e. you're connecting from the same computer), the connection is
considered secure and plaintext authentication is allowed.  See also
ssl=required setting.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer auth-cache-size
Authentication cache size (e.g. @samp{#e10e6}).  0 means it's disabled.
Note that bsdauth, PAM and vpopmail require @samp{cache-key} to be set for
caching to be used.  Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-cache-ttl
Time to live for cached data.  After TTL expires the cached record is no
longer used, *except* if the main database lookup returns internal failure.
We also try to handle password changes automatically: If user's previous
authentication was successful, but this one wasn't, the cache isn't used.
For now this works only with plaintext authentication.  Defaults to @samp{"1
hour"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-cache-negative-ttl
TTL for negative hits (user not found, password mismatch).  0 disables
caching them completely.  Defaults to @samp{"1 hour"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list auth-realms
List of realms for SASL authentication mechanisms that need them.  You can
leave it empty if you don't want to support multiple realms.  Many clients
simply use the first one listed here, so keep the default realm first.
Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-default-realm
Default realm/domain to use if none was specified.  This is used for both
SASL realms and appending @@domain to username in plaintext logins.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-username-chars
List of allowed characters in username.  If the user-given username contains
a character not listed in here, the login automatically fails.  This is just
an extra check to make sure user can't exploit any potential quote escaping
vulnerabilities with SQL/LDAP databases.  If you want to allow all
characters, set this value to empty.  Defaults to
@samp{"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.-_@@"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-username-translation
Username character translations before it's looked up from databases.  The
value contains series of from -> to characters.  For example @samp{#@@/@@}
means that @samp{#} and @samp{/} characters are translated to @samp{@@}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-username-format
Username formatting before it's looked up from databases.  You can use the
standard variables here, e.g. %Lu would lowercase the username, %n would
drop away the domain if it was given, or @samp{%n-AT-%d} would change the
@samp{@@} into @samp{-AT-}.  This translation is done after
@samp{auth-username-translation} changes.  Defaults to @samp{"%Lu"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-master-user-separator
If you want to allow master users to log in by specifying the master
username within the normal username string (i.e. not using SASL mechanism's
support for it), you can specify the separator character here.  The format
is then <username><separator><master username>.  UW-IMAP uses @samp{*} as
the separator, so that could be a good choice.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-anonymous-username
Username to use for users logging in with ANONYMOUS SASL mechanism.
Defaults to @samp{"anonymous"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer auth-worker-max-count
Maximum number of dovecot-auth worker processes.  They're used to execute
blocking passdb and userdb queries (e.g. MySQL and PAM).  They're
automatically created and destroyed as needed.  Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-gssapi-hostname
Host name to use in GSSAPI principal names.  The default is to use the name
returned by gethostname().  Use @samp{$ALL} (with quotes) to allow all
keytab entries.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-krb5-keytab
Kerberos keytab to use for the GSSAPI mechanism.  Will use the system
default (usually @file{/etc/krb5.keytab}) if not specified.  You may need to
change the auth service to run as root to be able to read this file.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-use-winbind?
Do NTLM and GSS-SPNEGO authentication using Samba's winbind daemon and
@samp{ntlm-auth} helper.  <doc/wiki/Authentication/Mechanisms/Winbind.txt>.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name auth-winbind-helper-path
Path for Samba's @samp{ntlm-auth} helper binary.  Defaults to
@samp{"/usr/bin/ntlm_auth"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-failure-delay
Time to delay before replying to failed authentications.  Defaults to
@samp{"2 secs"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-ssl-require-client-cert?
Require a valid SSL client certificate or the authentication fails.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-ssl-username-from-cert?
Take the username from client's SSL certificate, using
@code{X509_NAME_get_text_by_NID()} which returns the subject's DN's
CommonName.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list auth-mechanisms
List of wanted authentication mechanisms.  Supported mechanisms are:
@samp{plain}, @samp{login}, @samp{digest-md5}, @samp{cram-md5}, @samp{ntlm},
@samp{rpa}, @samp{apop}, @samp{anonymous}, @samp{gssapi}, @samp{otp},
@samp{skey}, and @samp{gss-spnego}.  NOTE: See also
@samp{disable-plaintext-auth} setting.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list director-servers
List of IPs or hostnames to all director servers, including ourself.  Ports
can be specified as ip:port.  The default port is the same as what director
service's @samp{inet-listener} is using.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list director-mail-servers
List of IPs or hostnames to all backend mail servers.  Ranges are allowed
too, like 10.0.0.10-10.0.0.30.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string director-user-expire
How long to redirect users to a specific server after it no longer has any
connections.  Defaults to @samp{"15 min"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string director-username-hash
How the username is translated before being hashed.  Useful values include
%Ln if user can log in with or without @@domain, %Ld if mailboxes are shared
within domain.  Defaults to @samp{"%Lu"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string log-path
Log file to use for error messages.  @samp{syslog} logs to syslog,
@samp{/dev/stderr} logs to stderr.  Defaults to @samp{"syslog"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string info-log-path
Log file to use for informational messages.  Defaults to @samp{log-path}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string debug-log-path
Log file to use for debug messages.  Defaults to @samp{info-log-path}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string syslog-facility
Syslog facility to use if you're logging to syslog.  Usually if you don't
want to use @samp{mail}, you'll use local0..local7.  Also other standard
facilities are supported.  Defaults to @samp{"mail"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-verbose?
Log unsuccessful authentication attempts and the reasons why they failed.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-verbose-passwords?
In case of password mismatches, log the attempted password.  Valid values
are no, plain and sha1.  sha1 can be useful for detecting brute force
password attempts vs.  user simply trying the same password over and over
again.  You can also truncate the value to n chars by appending ":n"
(e.g. sha1:6).  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-debug?
Even more verbose logging for debugging purposes.  Shows for example SQL
queries.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-debug-passwords?
In case of password mismatches, log the passwords and used scheme so the
problem can be debugged.  Enabling this also enables @samp{auth-debug}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-debug?
Enable mail process debugging.  This can help you figure out why Dovecot
isn't finding your mails.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean verbose-ssl?
Show protocol level SSL errors.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string log-timestamp
Prefix for each line written to log file.  % codes are in strftime(3)
format.  Defaults to @samp{"\"%b %d %H:%M:%S \""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list login-log-format-elements
List of elements we want to log.  The elements which have a non-empty
variable value are joined together to form a comma-separated string.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string login-log-format
Login log format.  %s contains @samp{login-log-format-elements} string, %$
contains the data we want to log.  Defaults to @samp{"%$: %s"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-log-prefix
Log prefix for mail processes.  See doc/wiki/Variables.txt for list of
possible variables you can use.  Defaults to
@samp{"\"%s(%u)<%@{pid@}><%@{session@}>: \""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string deliver-log-format
Format to use for logging mail deliveries.  You can use variables:
@table @code
@item %$
Delivery status message (e.g. @samp{saved to INBOX})
@item %m
Message-ID
@item %s
Subject
@item %f
From address
@item %p
Physical size
@item %w
Virtual size.
@end table
Defaults to @samp{"msgid=%m: %$"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-location
Location for users' mailboxes.  The default is empty, which means that
Dovecot tries to find the mailboxes automatically.  This won't work if the
user doesn't yet have any mail, so you should explicitly tell Dovecot the
full location.

If you're using mbox, giving a path to the INBOX file (e.g. /var/mail/%u)
isn't enough.  You'll also need to tell Dovecot where the other mailboxes
are kept.  This is called the "root mail directory", and it must be the
first path given in the @samp{mail-location} setting.

There are a few special variables you can use, eg.:

@table @samp
@item %u
username
@item %n
user part in user@@domain, same as %u if there's no domain
@item %d
domain part in user@@domain, empty if there's no domain
@item %h
home director
@end table

See doc/wiki/Variables.txt for full list.  Some examples:
@table @samp
@item maildir:~/Maildir
@item mbox:~/mail:INBOX=/var/mail/%u
@item mbox:/var/mail/%d/%1n/%n:INDEX=/var/indexes/%d/%1n/%
@end table
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-uid
System user and group used to access mails.  If you use multiple, userdb can
override these by returning uid or gid fields.  You can use either numbers
or names.  <doc/wiki/UserIds.txt>.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-gid

Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-privileged-group
Group to enable temporarily for privileged operations.  Currently this is
used only with INBOX when either its initial creation or dotlocking fails.
Typically this is set to "mail" to give access to /var/mail.  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-access-groups
Grant access to these supplementary groups for mail processes.  Typically
these are used to set up access to shared mailboxes.  Note that it may be
dangerous to set these if users can create symlinks (e.g. if "mail" group is
set here, ln -s /var/mail ~/mail/var could allow a user to delete others'
mailboxes, or ln -s /secret/shared/box ~/mail/mybox would allow reading
it).  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-full-filesystem-access?
Allow full file system access to clients.  There's no access checks other
than what the operating system does for the active UID/GID.  It works with
both maildir and mboxes, allowing you to prefix mailboxes names with
e.g. /path/ or ~user/.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mmap-disable?
Don't use mmap() at all.  This is required if you store indexes to shared
file systems (NFS or clustered file system).  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean dotlock-use-excl?
Rely on @samp{O_EXCL} to work when creating dotlock files.  NFS supports
@samp{O_EXCL} since version 3, so this should be safe to use nowadays by
default.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-fsync
When to use fsync() or fdatasync() calls:
@table @code
@item optimized
Whenever necessary to avoid losing important data
@item always
Useful with e.g. NFS when write()s are delayed
@item never
Never use it (best performance, but crashes can lose data).
@end table
Defaults to @samp{"optimized"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-nfs-storage?
Mail storage exists in NFS.  Set this to yes to make Dovecot flush NFS
caches whenever needed.  If you're using only a single mail server this
isn't needed.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-nfs-index?
Mail index files also exist in NFS.  Setting this to yes requires
@samp{mmap-disable? #t} and @samp{fsync-disable? #f}.  Defaults to
@samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string lock-method
Locking method for index files.  Alternatives are fcntl, flock and dotlock.
Dotlocking uses some tricks which may create more disk I/O than other
locking methods.  NFS users: flock doesn't work, remember to change
@samp{mmap-disable}.  Defaults to @samp{"fcntl"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name mail-temp-dir
Directory in which LDA/LMTP temporarily stores incoming mails >128 kB.
Defaults to @samp{"/tmp"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer first-valid-uid
Valid UID range for users.  This is mostly to make sure that users can't log
in as daemons or other system users.  Note that denying root logins is
hardcoded to dovecot binary and can't be done even if @samp{first-valid-uid}
is set to 0.  Defaults to @samp{500}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer last-valid-uid

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer first-valid-gid
Valid GID range for users.  Users having non-valid GID as primary group ID
aren't allowed to log in.  If user belongs to supplementary groups with
non-valid GIDs, those groups are not set.  Defaults to @samp{1}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer last-valid-gid

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mail-max-keyword-length
Maximum allowed length for mail keyword name.  It's only forced when trying
to create new keywords.  Defaults to @samp{50}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} colon-separated-file-name-list valid-chroot-dirs
List of directories under which chrooting is allowed for mail processes
(i.e. /var/mail will allow chrooting to /var/mail/foo/bar too).  This
setting doesn't affect @samp{login-chroot} @samp{mail-chroot} or auth chroot
settings.  If this setting is empty, "/./" in home dirs are ignored.
WARNING: Never add directories here which local users can modify, that may
lead to root exploit.  Usually this should be done only if you don't allow
shell access for users.  <doc/wiki/Chrooting.txt>.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-chroot
Default chroot directory for mail processes.  This can be overridden for
specific users in user database by giving /./ in user's home directory
(e.g. /home/./user chroots into /home).  Note that usually there is no real
need to do chrooting, Dovecot doesn't allow users to access files outside
their mail directory anyway.  If your home directories are prefixed with the
chroot directory, append "/." to @samp{mail-chroot}.
<doc/wiki/Chrooting.txt>.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name auth-socket-path
UNIX socket path to master authentication server to find users.  This is
used by imap (for shared users) and lda.  Defaults to
@samp{"/var/run/dovecot/auth-userdb"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name mail-plugin-dir
Directory where to look up mail plugins.  Defaults to
@samp{"/usr/lib/dovecot"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list mail-plugins
List of plugins to load for all services.  Plugins specific to IMAP, LDA,
etc. are added to this list in their own .conf files.  Defaults to
@samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mail-cache-min-mail-count
The minimum number of mails in a mailbox before updates are done to cache
file.  This allows optimizing Dovecot's behavior to do less disk writes at
the cost of more disk reads.  Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mailbox-idle-check-interval
When IDLE command is running, mailbox is checked once in a while to see if
there are any new mails or other changes.  This setting defines the minimum
time to wait between those checks.  Dovecot can also use dnotify, inotify
and kqueue to find out immediately when changes occur.  Defaults to
@samp{"30 secs"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-save-crlf?
Save mails with CR+LF instead of plain LF.  This makes sending those mails
take less CPU, especially with sendfile() syscall with Linux and FreeBSD.
But it also creates a bit more disk I/O which may just make it slower.  Also
note that if other software reads the mboxes/maildirs, they may handle the
extra CRs wrong and cause problems.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean maildir-stat-dirs?
By default LIST command returns all entries in maildir beginning with a
dot.  Enabling this option makes Dovecot return only entries which are
directories.  This is done by stat()ing each entry, so it causes more disk
I/O.  (For systems setting struct @samp{dirent->d_type} this check is free
and it's done always regardless of this setting).  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean maildir-copy-with-hardlinks?
When copying a message, do it with hard links whenever possible.  This makes
the performance much better, and it's unlikely to have any side effects.
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean maildir-very-dirty-syncs?
Assume Dovecot is the only MUA accessing Maildir: Scan cur/ directory only
when its mtime changes unexpectedly or when we can't find the mail
otherwise.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list mbox-read-locks
Which locking methods to use for locking mbox.  There are four available:

@table @code
@item dotlock
Create <mailbox>.lock file.  This is the oldest and most NFS-safe solution.
If you want to use /var/mail/ like directory, the users will need write
access to that directory.
@item dotlock-try
Same as dotlock, but if it fails because of permissions or because there
isn't enough disk space, just skip it.
@item fcntl
Use this if possible.  Works with NFS too if lockd is used.
@item flock
May not exist in all systems.  Doesn't work with NFS.
@item lockf
May not exist in all systems.  Doesn't work with NFS.
@end table

You can use multiple locking methods; if you do the order they're declared
in is important to avoid deadlocks if other MTAs/MUAs are using multiple
locking methods as well.  Some operating systems don't allow using some of
them simultaneously.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list mbox-write-locks

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mbox-lock-timeout
Maximum time to wait for lock (all of them) before aborting.  Defaults to
@samp{"5 mins"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mbox-dotlock-change-timeout
If dotlock exists but the mailbox isn't modified in any way, override the
lock file after this much time.  Defaults to @samp{"2 mins"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mbox-dirty-syncs?
When mbox changes unexpectedly we have to fully read it to find out what
changed.  If the mbox is large this can take a long time.  Since the change
is usually just a newly appended mail, it'd be faster to simply read the new
mails.  If this setting is enabled, Dovecot does this but still safely
fallbacks to re-reading the whole mbox file whenever something in mbox isn't
how it's expected to be.  The only real downside to this setting is that if
some other MUA changes message flags, Dovecot doesn't notice it
immediately.  Note that a full sync is done with SELECT, EXAMINE, EXPUNGE
and CHECK commands.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mbox-very-dirty-syncs?
Like @samp{mbox-dirty-syncs}, but don't do full syncs even with SELECT,
EXAMINE, EXPUNGE or CHECK commands.  If this is set, @samp{mbox-dirty-syncs}
is ignored.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mbox-lazy-writes?
Delay writing mbox headers until doing a full write sync (EXPUNGE and CHECK
commands and when closing the mailbox).  This is especially useful for POP3
where clients often delete all mails.  The downside is that our changes
aren't immediately visible to other MUAs.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mbox-min-index-size
If mbox size is smaller than this (e.g. 100k), don't write index files.  If
an index file already exists it's still read, just not updated.  Defaults to
@samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mdbox-rotate-size
Maximum dbox file size until it's rotated.  Defaults to @samp{10000000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mdbox-rotate-interval
Maximum dbox file age until it's rotated.  Typically in days.  Day begins
from midnight, so 1d = today, 2d = yesterday, etc.  0 = check disabled.
Defaults to @samp{"1d"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mdbox-preallocate-space?
When creating new mdbox files, immediately preallocate their size to
@samp{mdbox-rotate-size}.  This setting currently works only in Linux with
some file systems (ext4, xfs).  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attachment-dir
sdbox and mdbox support saving mail attachments to external files, which
also allows single instance storage for them.  Other backends don't support
this for now.

WARNING: This feature hasn't been tested much yet.  Use at your own risk.

Directory root where to store mail attachments.  Disabled, if empty.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mail-attachment-min-size
Attachments smaller than this aren't saved externally.  It's also possible
to write a plugin to disable saving specific attachments externally.
Defaults to @samp{128000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attachment-fs
File system backend to use for saving attachments:
@table @code
@item posix
No SiS done by Dovecot (but this might help FS's own deduplication)
@item sis posix
SiS with immediate byte-by-byte comparison during saving
@item sis-queue posix
SiS with delayed comparison and deduplication.
@end table
Defaults to @samp{"sis posix"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attachment-hash
Hash format to use in attachment filenames.  You can add any text and
variables: @code{%@{md4@}}, @code{%@{md5@}}, @code{%@{sha1@}},
@code{%@{sha256@}}, @code{%@{sha512@}}, @code{%@{size@}}.  Variables can be
truncated, e.g. @code{%@{sha256:80@}} returns only first 80 bits.  Defaults
to @samp{"%@{sha1@}"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer default-process-limit

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer default-client-limit

Defaults to @samp{1000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer default-vsz-limit
Default VSZ (virtual memory size) limit for service processes.  This is
mainly intended to catch and kill processes that leak memory before they eat
up everything.  Defaults to @samp{256000000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string default-login-user
Login user is internally used by login processes.  This is the most
untrusted user in Dovecot system.  It shouldn't have access to anything at
all.  Defaults to @samp{"dovenull"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string default-internal-user
Internal user is used by unprivileged processes.  It should be separate from
login user, so that login processes can't disturb other processes.  Defaults
to @samp{"dovecot"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl?
SSL/TLS support: yes, no, required.  <doc/wiki/SSL.txt>.  Defaults to
@samp{"required"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-cert
PEM encoded X.509 SSL/TLS certificate (public key).  Defaults to
@samp{"</etc/dovecot/default.pem"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-key
PEM encoded SSL/TLS private key.  The key is opened before dropping root
privileges, so keep the key file unreadable by anyone but root.  Defaults to
@samp{"</etc/dovecot/private/default.pem"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-key-password
If key file is password protected, give the password here.  Alternatively
give it when starting dovecot with -p parameter.  Since this file is often
world-readable, you may want to place this setting instead to a different.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-ca
PEM encoded trusted certificate authority.  Set this only if you intend to
use @samp{ssl-verify-client-cert? #t}.  The file should contain the CA
certificate(s) followed by the matching CRL(s).  (e.g. @samp{ssl-ca
</etc/ssl/certs/ca.pem}).  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean ssl-require-crl?
Require that CRL check succeeds for client certificates.  Defaults to
@samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean ssl-verify-client-cert?
Request client to send a certificate.  If you also want to require it, set
@samp{auth-ssl-require-client-cert? #t} in auth section.  Defaults to
@samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-cert-username-field
Which field from certificate to use for username.  commonName and
x500UniqueIdentifier are the usual choices.  You'll also need to set
@samp{auth-ssl-username-from-cert? #t}.  Defaults to @samp{"commonName"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-min-protocol
Minimum SSL protocol version to accept.  Defaults to @samp{"TLSv1"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-cipher-list
SSL ciphers to use.  Defaults to
@samp{"ALL:!kRSA:!SRP:!kDHd:!DSS:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK:!RC4:!ADH:!LOW@@STRENGTH"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-crypto-device
SSL crypto device to use, for valid values run "openssl engine".  Defaults
to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string postmaster-address
Address to use when sending rejection mails.  %d expands to recipient
domain.  Defaults to @samp{"postmaster@@%d"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string hostname
Hostname to use in various parts of sent mails (e.g. in Message-Id)  and in
LMTP replies.  Default is the system's real hostname@@domain.  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean quota-full-tempfail?
If user is over quota, return with temporary failure instead of bouncing the
mail.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name sendmail-path
Binary to use for sending mails.  Defaults to @samp{"/usr/sbin/sendmail"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string submission-host
If non-empty, send mails via this SMTP host[:port] instead of sendmail.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string rejection-subject
Subject: header to use for rejection mails.  You can use the same variables
as for @samp{rejection-reason} below.  Defaults to @samp{"Rejected: %s"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string rejection-reason
Human readable error message for rejection mails.  You can use variables:

@table @code
@item %n
CRLF
@item %r
reason
@item %s
original subject
@item %t
recipient
@end table
Defaults to @samp{"Your message to <%t> was automatically rejected:%n%r"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string recipient-delimiter
Delimiter character between local-part and detail in email address.
Defaults to @samp{"+"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string lda-original-recipient-header
Header where the original recipient address (SMTP's RCPT TO: address) is
taken from if not available elsewhere.  With dovecot-lda -a parameter
overrides this.  A commonly used header for this is X-Original-To.  Defaults
to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean lda-mailbox-autocreate?
Should saving a mail to a nonexistent mailbox automatically create it?.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean lda-mailbox-autosubscribe?
Should automatically created mailboxes be also automatically subscribed?.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer imap-max-line-length
Maximum IMAP command line length.  Some clients generate very long command
lines with huge mailboxes, so you may need to raise this if you get "Too
long argument" or "IMAP command line too large" errors often.  Defaults to
@samp{64000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-logout-format
IMAP logout format string:
@table @code
@item %i
total number of bytes read from client
@item %o
total number of bytes sent to client.
@end table
See @file{doc/wiki/Variables.txt} for a list of all the variables you can
use.  Defaults to @samp{"in=%i out=%o deleted=%@{deleted@}
expunged=%@{expunged@} trashed=%@{trashed@} hdr_count=%@{fetch_hdr_count@}
hdr_bytes=%@{fetch_hdr_bytes@} body_count=%@{fetch_body_count@}
body_bytes=%@{fetch_body_bytes@}"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-capability
Override the IMAP CAPABILITY response.  If the value begins with '+', add
the given capabilities on top of the defaults (e.g. +XFOO XBAR).  Defaults
to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-idle-notify-interval
How long to wait between "OK Still here" notifications when client is
IDLEing.  Defaults to @samp{"2 mins"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-id-send
ID field names and values to send to clients.  Using * as the value makes
Dovecot use the default value.  The following fields have default values
currently: name, version, os, os-version, support-url, support-email.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-id-log
ID fields sent by client to log.  * means everything.  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list imap-client-workarounds
Workarounds for various client bugs:

@table @code
@item delay-newmail
Send EXISTS/RECENT new mail notifications only when replying to NOOP and
CHECK commands.  Some clients ignore them otherwise, for example OSX Mail
(<v2.1).  Outlook Express breaks more badly though, without this it may show
user "Message no longer in server" errors.  Note that OE6 still breaks even
with this workaround if synchronization is set to "Headers Only".

@item tb-extra-mailbox-sep
Thunderbird gets somehow confused with LAYOUT=fs (mbox and dbox) and adds
extra @samp{/} suffixes to mailbox names.  This option causes Dovecot to
ignore the extra @samp{/} instead of treating it as invalid mailbox name.

@item tb-lsub-flags
Show \Noselect flags for LSUB replies with LAYOUT=fs (e.g. mbox).  This
makes Thunderbird realize they aren't selectable and show them greyed out,
instead of only later giving "not selectable" popup error.
@end table
Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-urlauth-host
Host allowed in URLAUTH URLs sent by client.  "*" allows all.  Defaults to
@samp{""}.
@end deftypevr


Whew! Lots of configuration options.  The nice thing about it though is that
GuixSD has a complete interface to Dovecot's configuration language.  This
allows not only a nice way to declare configurations, but also offers
reflective capabilities as well: users can write code to inspect and
transform configurations from within Scheme.

However, it could be that you just want to get a @code{dovecot.conf} up and
running.  In that case, you can pass an @code{opaque-dovecot-configuration}
as the @code{#:config} parameter to @code{dovecot-service}.  As its name
indicates, an opaque configuration does not have easy reflective
capabilities.

Available @code{opaque-dovecot-configuration} fields are:

@deftypevr {@code{opaque-dovecot-configuration} parameter} package dovecot
The dovecot package.
@end deftypevr

@deftypevr {@code{opaque-dovecot-configuration} parameter} string string
The contents of the @code{dovecot.conf}, as a string.
@end deftypevr

For example, if your @code{dovecot.conf} is just the empty string, you could
instantiate a dovecot service like this:

@example
(dovecot-service #:config
                 (opaque-dovecot-configuration
                  (string "")))
@end example

@subsubheading OpenSMTPD Service

@deffn {Scheme Variable} opensmtpd-service-type
This is the type of the @uref{https://www.opensmtpd.org, OpenSMTPD} service,
whose value should be an @code{opensmtpd-configuration} object as in this
example:

@example
(service opensmtpd-service-type
         (opensmtpd-configuration
           (config-file (local-file "./my-smtpd.conf"))))
@end example
@end deffn

@deftp {Data Type} opensmtpd-configuration
Data type representing the configuration of opensmtpd.

@table @asis
@item @code{package} (default: @var{opensmtpd})
Package object of the OpenSMTPD SMTP server.

@item @code{config-file} (default: @var{%default-opensmtpd-file})
File-like object of the OpenSMTPD configuration file to use.  By default it
listens on the loopback network interface, and allows for mail from users
and daemons on the local machine, as well as permitting email to remote
servers.  Run @command{man smtpd.conf} for more information.

@end table
@end deftp

@subsubheading Exim Service

@cindex mail transfer agent (MTA)
@cindex MTA (mail transfer agent)
@cindex SMTP

@deffn {Scheme Variable} exim-service-type
This is the type of the @uref{https://exim.org, Exim} mail transfer agent
(MTA), whose value should be an @code{exim-configuration} object as in this
example:

@example
(service exim-service-type
         (exim-configuration
           (config-file (local-file "./my-exim.conf"))))
@end example
@end deffn

In order to use an @code{exim-service-type} service you must also have a
@code{mail-aliases-service-type} service present in your
@code{operating-system} (even if it has no aliases).

@deftp {Data Type} exim-configuration
Data type representing the configuration of exim.

@table @asis
@item @code{package} (default: @var{exim})
Package object of the Exim server.

@item @code{config-file} (default: @code{#f})
File-like object of the Exim configuration file to use. If its value is
@code{#f} then use the default configuration file from the package provided
in @code{package}. The resulting configuration file is loaded after setting
the @code{exim_user} and @code{exim_group} configuration variables.

@end table
@end deftp

@subsubheading Mail Aliases Service

@cindex email aliases
@cindex aliases, for email addresses

@deffn {Scheme Variable} mail-aliases-service-type
This is the type of the service which provides @code{/etc/aliases},
specifying how to deliver mail to users on this system.

@example
(service mail-aliases-service-type
         '(("postmaster" "bob")
           ("bob" "bob@@example.com" "bob@@example2.com")))
@end example
@end deffn

The configuration for a @code{mail-aliases-service-type} service is an
association list denoting how to deliver mail that comes to this
system. Each entry is of the form @code{(alias addresses ...)}, with
@code{alias} specifying the local alias and @code{addresses} specifying
where to deliver this user's mail.

The aliases aren't required to exist as users on the local system. In the
above example, there doesn't need to be a @code{postmaster} entry in the
@code{operating-system}'s @code{user-accounts} in order to deliver the
@code{postmaster} mail to @code{bob} (which subsequently would deliver mail
to @code{bob@@example.com} and @code{bob@@example2.com}).

@node Kurznachrichtendienste
@subsubsection Kurznachrichtendienste

@cindex messaging
@cindex jabber
@cindex XMPP
The @code{(gnu services messaging)} module provides Guix service definitions
for messaging services: currently only Prosody is supported.

@subsubheading Prosody Service

@deffn {Scheme Variable} prosody-service-type
This is the type for the @uref{https://prosody.im, Prosody XMPP
communication server}.  Its value must be a @code{prosody-configuration}
record as in this example:

@example
(service prosody-service-type
         (prosody-configuration
          (modules-enabled (cons "groups" "mam" %default-modules-enabled))
          (int-components
           (list
            (int-component-configuration
             (hostname "conference.example.net")
             (plugin "muc")
             (mod-muc (mod-muc-configuration)))))
          (virtualhosts
           (list
            (virtualhost-configuration
             (domain "example.net"))))))
@end example

See below for details about @code{prosody-configuration}.

@end deffn

By default, Prosody does not need much configuration.  Only one
@code{virtualhosts} field is needed: it specifies the domain you wish
Prosody to serve.

You can perform various sanity checks on the generated configuration with
the @code{prosodyctl check} command.

Prosodyctl will also help you to import certificates from the
@code{letsencrypt} directory so that the @code{prosody} user can access
them.  See @url{https://prosody.im/doc/letsencrypt}.

@example
prosodyctl --root cert import /etc/letsencrypt/live
@end example

The available configuration parameters follow.  Each parameter definition is
preceded by its type; for example, @samp{string-list foo} indicates that the
@code{foo} parameter should be specified as a list of strings.  Types
starting with @code{maybe-} denote parameters that won't show up in
@code{prosody.cfg.lua} when their value is @code{'disabled}.

There is also a way to specify the configuration as a string, if you have an
old @code{prosody.cfg.lua} file that you want to port over from some other
system; see the end for more details.

The @code{file-object} type designates either a file-like object
(@pxref{G-Ausdrücke, file-like objects}) or a file name.

@c The following documentation was initially generated by
@c (generate-documentation) in (gnu services messaging).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as Prosody updates.

Available @code{prosody-configuration} fields are:

@deftypevr {@code{prosody-configuration} parameter} package prosody
The Prosody package.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-name data-path
Location of the Prosody data storage directory.  See
@url{https://prosody.im/doc/configure}.  Defaults to
@samp{"/var/lib/prosody"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-object-list plugin-paths
Additional plugin directories.  They are searched in all the specified paths
in order.  See @url{https://prosody.im/doc/plugins_directory}.  Defaults to
@samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-name certificates
Every virtual host and component needs a certificate so that clients and
servers can securely verify its identity.  Prosody will automatically load
certificates/keys from the directory specified here.  Defaults to
@samp{"/etc/prosody/certs"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list admins
This is a list of accounts that are admins for the server.  Note that you
must create the accounts separately.  See
@url{https://prosody.im/doc/admins} and
@url{https://prosody.im/doc/creating_accounts}.  Example: @code{(admins
'("user1@@example.com" "user2@@example.net"))} Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean use-libevent?
Enable use of libevent for better performance under high load.  See
@url{https://prosody.im/doc/libevent}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} module-list modules-enabled
This is the list of modules Prosody will load on startup.  It looks for
@code{mod_modulename.lua} in the plugins folder, so make sure that exists
too.  Documentation on modules can be found at:
@url{https://prosody.im/doc/modules}.  Defaults to @samp{("roster"
"saslauth" "tls" "dialback" "disco" "carbons" "private" "blocklist" "vcard"
"version" "uptime" "time" "ping" "pep" "register" "admin_adhoc")}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list modules-disabled
@samp{"offline"}, @samp{"c2s"} and @samp{"s2s"} are auto-loaded, but should
you want to disable them then add them to this list.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-object groups-file
Path to a text file where the shared groups are defined.  If this path is
empty then @samp{mod_groups} does nothing.  See
@url{https://prosody.im/doc/modules/mod_groups}.  Defaults to
@samp{"/var/lib/prosody/sharedgroups.txt"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean allow-registration?
Disable account creation by default, for security.  See
@url{https://prosody.im/doc/creating_accounts}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-ssl-configuration ssl
These are the SSL/TLS-related settings.  Most of them are disabled so to use
Prosody's defaults.  If you do not completely understand these options, do
not add them to your config, it is easy to lower the security of your server
using them.  See @url{https://prosody.im/doc/advanced_ssl_config}.

Available @code{ssl-configuration} fields are:

@deftypevr {@code{ssl-configuration} parameter} maybe-string protocol
This determines what handshake to use.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-name key
Path to your private key file.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-name certificate
Path to your certificate file.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} file-object capath
Path to directory containing root certificates that you wish Prosody to
trust when verifying the certificates of remote servers.  Defaults to
@samp{"/etc/ssl/certs"}.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-object cafile
Path to a file containing root certificates that you wish Prosody to trust.
Similar to @code{capath} but with all certificates concatenated together.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string-list verify
A list of verification options (these mostly map to OpenSSL's
@code{set_verify()} flags).
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string-list options
A list of general options relating to SSL/TLS.  These map to OpenSSL's
@code{set_options()}.  For a full list of options available in LuaSec, see
the LuaSec source.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-non-negative-integer depth
How long a chain of certificate authorities to check when looking for a
trusted root certificate.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string ciphers
An OpenSSL cipher string.  This selects what ciphers Prosody will offer to
clients, and in what order.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-name dhparam
A path to a file containing parameters for Diffie-Hellman key exchange.  You
can create such a file with: @code{openssl dhparam -out
/etc/prosody/certs/dh-2048.pem 2048}
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string curve
Curve for Elliptic curve Diffie-Hellman. Prosody's default is
@samp{"secp384r1"}.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string-list verifyext
A list of "extra" verification options.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string password
Password for encrypted private keys.
@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean c2s-require-encryption?
Whether to force all client-to-server connections to be encrypted or not.
See @url{https://prosody.im/doc/modules/mod_tls}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list disable-sasl-mechanisms
Set of mechanisms that will never be offered.  See
@url{https://prosody.im/doc/modules/mod_saslauth}.  Defaults to
@samp{("DIGEST-MD5")}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean s2s-require-encryption?
Whether to force all server-to-server connections to be encrypted or not.
See @url{https://prosody.im/doc/modules/mod_tls}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean s2s-secure-auth?
Whether to require encryption and certificate authentication.  This provides
ideal security, but requires servers you communicate with to support
encryption AND present valid, trusted certificates.  See
@url{https://prosody.im/doc/s2s#security}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list s2s-insecure-domains
Many servers don't support encryption or have invalid or self-signed
certificates.  You can list domains here that will not be required to
authenticate using certificates.  They will be authenticated using DNS.  See
@url{https://prosody.im/doc/s2s#security}.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list s2s-secure-domains
Even if you leave @code{s2s-secure-auth?} disabled, you can still require
valid certificates for some domains by specifying a list here.  See
@url{https://prosody.im/doc/s2s#security}.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string authentication
Select the authentication backend to use.  The default provider stores
passwords in plaintext and uses Prosody's configured data storage to store
the authentication data.  If you do not trust your server please see
@url{https://prosody.im/doc/modules/mod_auth_internal_hashed} for
information about using the hashed backend.  See also
@url{https://prosody.im/doc/authentication} Defaults to
@samp{"internal_plain"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-string log
Set logging options.  Advanced logging configuration is not yet supported by
the GuixSD Prosody Service.  See @url{https://prosody.im/doc/logging}.
Defaults to @samp{"*syslog"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-name pidfile
File to write pid in.  See @url{https://prosody.im/doc/modules/mod_posix}.
Defaults to @samp{"/var/run/prosody/prosody.pid"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-non-negative-integer http-max-content-size
Maximum allowed size of the HTTP body (in bytes).
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-string http-external-url
Some modules expose their own URL in various ways.  This URL is built from
the protocol, host and port used.  If Prosody sits behind a proxy, the
public URL will be @code{http-external-url} instead.  See
@url{https://prosody.im/doc/http#external_url}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} virtualhost-configuration-list virtualhosts
A host in Prosody is a domain on which user accounts can be created.  For
example if you want your users to have addresses like
@samp{"john.smith@@example.com"} then you need to add a host
@samp{"example.com"}.  All options in this list will apply only to this
host.

Note: the name "virtual" host is used in configuration to avoid confusion
with the actual physical host that Prosody is installed on.  A single
Prosody instance can serve many domains, each one defined as a VirtualHost
entry in Prosody's configuration.  Conversely a server that hosts a single
domain would have just one VirtualHost entry.

See @url{https://prosody.im/doc/configure#virtual_host_settings}.

Available @code{virtualhost-configuration} fields are:

all these @code{prosody-configuration} fields: @code{admins},
@code{use-libevent?}, @code{modules-enabled}, @code{modules-disabled},
@code{groups-file}, @code{allow-registration?}, @code{ssl},
@code{c2s-require-encryption?}, @code{disable-sasl-mechanisms},
@code{s2s-require-encryption?}, @code{s2s-secure-auth?},
@code{s2s-insecure-domains}, @code{s2s-secure-domains},
@code{authentication}, @code{log}, @code{http-max-content-size},
@code{http-external-url}, @code{raw-content}, plus:
@deftypevr {@code{virtualhost-configuration} parameter} string domain
Domain you wish Prosody to serve.
@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} int-component-configuration-list int-components
Components are extra services on a server which are available to clients,
usually on a subdomain of the main server (such as
@samp{"mycomponent.example.com"}).  Example components might be chatroom
servers, user directories, or gateways to other protocols.

Internal components are implemented with Prosody-specific plugins.  To add
an internal component, you simply fill the hostname field, and the plugin
you wish to use for the component.

See @url{https://prosody.im/doc/components}.  Defaults to @samp{()}.

Available @code{int-component-configuration} fields are:

all these @code{prosody-configuration} fields: @code{admins},
@code{use-libevent?}, @code{modules-enabled}, @code{modules-disabled},
@code{groups-file}, @code{allow-registration?}, @code{ssl},
@code{c2s-require-encryption?}, @code{disable-sasl-mechanisms},
@code{s2s-require-encryption?}, @code{s2s-secure-auth?},
@code{s2s-insecure-domains}, @code{s2s-secure-domains},
@code{authentication}, @code{log}, @code{http-max-content-size},
@code{http-external-url}, @code{raw-content}, plus:
@deftypevr {@code{int-component-configuration} parameter} string hostname
Hostname of the component.
@end deftypevr

@deftypevr {@code{int-component-configuration} parameter} string plugin
Plugin you wish to use for the component.
@end deftypevr

@deftypevr {@code{int-component-configuration} parameter} maybe-mod-muc-configuration mod-muc
Multi-user chat (MUC) is Prosody's module for allowing you to create hosted
chatrooms/conferences for XMPP users.

General information on setting up and using multi-user chatrooms can be
found in the "Chatrooms" documentation
(@url{https://prosody.im/doc/chatrooms}), which you should read if you are
new to XMPP chatrooms.

See also @url{https://prosody.im/doc/modules/mod_muc}.

Available @code{mod-muc-configuration} fields are:

@deftypevr {@code{mod-muc-configuration} parameter} string name
The name to return in service discovery responses.  Defaults to
@samp{"Prosody Chatrooms"}.
@end deftypevr

@deftypevr {@code{mod-muc-configuration} parameter} string-or-boolean restrict-room-creation
If @samp{#t}, this will only allow admins to create new chatrooms.
Otherwise anyone can create a room.  The value @samp{"local"} restricts room
creation to users on the service's parent domain.
E.g. @samp{user@@example.com} can create rooms on @samp{rooms.example.com}.
The value @samp{"admin"} restricts to service administrators only.  Defaults
to @samp{#f}.
@end deftypevr

@deftypevr {@code{mod-muc-configuration} parameter} non-negative-integer max-history-messages
Maximum number of history messages that will be sent to the member that has
just joined the room.  Defaults to @samp{20}.
@end deftypevr

@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} ext-component-configuration-list ext-components
External components use XEP-0114, which most standalone components support.
To add an external component, you simply fill the hostname field.  See
@url{https://prosody.im/doc/components}.  Defaults to @samp{()}.

Available @code{ext-component-configuration} fields are:

all these @code{prosody-configuration} fields: @code{admins},
@code{use-libevent?}, @code{modules-enabled}, @code{modules-disabled},
@code{groups-file}, @code{allow-registration?}, @code{ssl},
@code{c2s-require-encryption?}, @code{disable-sasl-mechanisms},
@code{s2s-require-encryption?}, @code{s2s-secure-auth?},
@code{s2s-insecure-domains}, @code{s2s-secure-domains},
@code{authentication}, @code{log}, @code{http-max-content-size},
@code{http-external-url}, @code{raw-content}, plus:
@deftypevr {@code{ext-component-configuration} parameter} string component-secret
Password which the component will use to log in.
@end deftypevr

@deftypevr {@code{ext-component-configuration} parameter} string hostname
Hostname of the component.
@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} non-negative-integer-list component-ports
Port(s) Prosody listens on for component connections.  Defaults to
@samp{(5347)}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string component-interface
Interface Prosody listens on for component connections.  Defaults to
@samp{"127.0.0.1"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-raw-content raw-content
Raw content that will be added to the configuration file.
@end deftypevr

It could be that you just want to get a @code{prosody.cfg.lua} up and
running.  In that case, you can pass an @code{opaque-prosody-configuration}
record as the value of @code{prosody-service-type}.  As its name indicates,
an opaque configuration does not have easy reflective capabilities.
Available @code{opaque-prosody-configuration} fields are:

@deftypevr {@code{opaque-prosody-configuration} parameter} package prosody
The prosody package.
@end deftypevr

@deftypevr {@code{opaque-prosody-configuration} parameter} string prosody.cfg.lua
The contents of the @code{prosody.cfg.lua} to use.
@end deftypevr

For example, if your @code{prosody.cfg.lua} is just the empty string, you
could instantiate a prosody service like this:

@example
(service prosody-service-type
         (opaque-prosody-configuration
          (prosody.cfg.lua "")))
@end example

@c end of Prosody auto-generated documentation

@subsubheading BitlBee Service

@cindex IRC (Internet Relay Chat)
@cindex IRC gateway
@url{http://bitlbee.org,BitlBee} is a gateway that provides an IRC interface
to a variety of messaging protocols such as XMPP.

@defvr {Scheme Variable} bitlbee-service-type
This is the service type for the @url{http://bitlbee.org,BitlBee} IRC
gateway daemon.  Its value is a @code{bitlbee-configuration} (see below).

To have BitlBee listen on port 6667 on localhost, add this line to your
services:

@example
(service bitlbee-service-type)
@end example
@end defvr

@deftp {Data Type} bitlbee-configuration
This is the configuration for BitlBee, with the following fields:

@table @asis
@item @code{interface} (default: @code{"127.0.0.1"})
@itemx @code{port} (default: @code{6667})
Listen on the network interface corresponding to the IP address specified in
@var{interface}, on @var{port}.

When @var{interface} is @code{127.0.0.1}, only local clients can connect;
when it is @code{0.0.0.0}, connections can come from any networking
interface.

@item @code{package} (default: @code{bitlbee})
The BitlBee package to use.

@item @code{plugins} (default: @code{'()})
List of plugin packages to use---e.g., @code{bitlbee-discord}.

@item @code{extra-settings} (default: @code{""})
Configuration snippet added as-is to the BitlBee configuration file.
@end table
@end deftp


@node Telefondienste
@subsubsection Telefondienste

@cindex Murmur (VoIP server)
@cindex VoIP server
This section describes how to set up and run a Murmur server.  Murmur is the
server of the @uref{https://mumble.info, Mumble} voice-over-IP (VoIP) suite.

@deftp {Data Type} murmur-configuration
The service type for the Murmur server.  An example configuration can look
like this:

@example
(service murmur-service-type
         (murmur-configuration
          (welcome-text
            "Welcome to this Mumble server running on GuixSD!")
          (cert-required? #t) ;disallow text password logins
          (ssl-cert "/etc/letsencrypt/live/mumble.example.com/fullchain.pem")
          (ssl-key "/etc/letsencrypt/live/mumble.example.com/privkey.pem")))
@end example

After reconfiguring your system, you can manually set the murmur
@code{SuperUser} password with the command that is printed during the
activation phase.

It is recommended to register a normal Mumble user account and grant it
admin or moderator rights.  You can use the @code{mumble} client to login as
new normal user, register yourself, and log out.  For the next step login
with the name @code{SuperUser} use the @code{SuperUser} password that you
set previously, and grant your newly registered mumble user administrator or
moderator rights and create some channels.

Available @code{murmur-configuration} fields are:

@table @asis
@item @code{package} (default: @code{mumble})
Package that contains @code{bin/murmurd}.

@item @code{user} (default: @code{"murmur"})
User who will run the Murmur server.

@item @code{group} (default: @code{"murmur"})
Group of the user who will run the murmur server.

@item @code{port} (default: @code{64738})
Port on which the server will listen.

@item @code{welcome-text} (default: @code{""})
Welcome text sent to clients when they connect.

@item @code{server-password} (default: @code{""})
Password the clients have to enter in order to connect.

@item @code{max-users} (default: @code{100})
Maximum of users that can be connected to the server at once.

@item @code{max-user-bandwidth} (default: @code{#f})
Maximum voice traffic a user can send per second.

@item @code{database-file} (default: @code{"/var/lib/murmur/db.sqlite"})
File name of the sqlite database.  The service's user will become the owner
of the directory.

@item @code{log-file} (default: @code{"/var/log/murmur/murmur.log"})
File name of the log file.  The service's user will become the owner of the
directory.

@item @code{autoban-attempts} (default: @code{10})
Maximum number of logins a user can make in @code{autoban-timeframe} without
getting auto banned for @code{autoban-time}.

@item @code{autoban-timeframe} (default: @code{120})
Timeframe for autoban in seconds.

@item @code{autoban-time} (default: @code{300})
Amount of time in seconds for which a client gets banned when violating the
autoban limits.

@item @code{opus-threshold} (default: @code{100})
Percentage of clients that need to support opus before switching over to
opus audio codec.

@item @code{channel-nesting-limit} (default: @code{10})
How deep channels can be nested at maximum.

@item @code{channelname-regex} (default: @code{#f})
A string in from of a Qt regular expression that channel names must conform
to.

@item @code{username-regex} (default: @code{#f})
A string in from of a Qt regular expression that user names must conform to.

@item @code{text-message-length} (default: @code{5000})
Maximum size in bytes that a user can send in one text chat message.

@item @code{image-message-length} (default: @code{(* 128 1024)})
Maximum size in bytes that a user can send in one image message.

@item @code{cert-required?} (default: @code{#f})
If it is set to @code{#t} clients that use weak password authentification
will not be accepted. Users must have completed the certificate wizard to
join.

@item @code{remember-channel?} (defualt @code{#f})
Should murmur remember the last channel each user was in when they
disconnected and put them into the remembered channel when they rejoin.

@item @code{allow-html?} (default: @code{#f})
Should html be allowed in text messages, user comments, and channel
descriptions.

@item @code{allow-ping?} (default: @code{#f})
Setting to true exposes the current user count, the maximum user count, and
the server's maximum bandwidth per client to unauthenticated users. In the
Mumble client, this information is shown in the Connect dialog.

Disabling this setting will prevent public listing of the server.

@item @code{bonjour?} (default: @code{#f})
Should the server advertise itself in the local network through the bonjour
protocol.

@item @code{send-version?} (default: @code{#f})
Should the murmur server version be exposed in ping requests.

@item @code{log-days} (default: @code{31})
Murmur also stores logs in the database, which are accessible via RPC.  The
default is 31 days of months, but you can set this setting to 0 to keep logs
forever, or -1 to disable logging to the database.

@item @code{obfuscate-ips?} (default @code{#t})
Should logged ips be obfuscated to protect the privacy of users.

@item @code{ssl-cert} (default: @code{#f})
File name of the SSL/TLS certificate used for encrypted connections.

@example
(ssl-cert "/etc/letsencrypt/live/example.com/fullchain.pem")
@end example
@item @code{ssl-key} (default: @code{#f})
Filepath to the ssl private key used for encrypted connections.
@example
(ssl-key "/etc/letsencrypt/live/example.com/privkey.pem")
@end example

@item @code{ssl-dh-params} (default: @code{#f})
File name of a PEM-encoded file with Diffie-Hellman parameters for the
SSL/TLS encryption.  Alternatively you set it to @code{"@@ffdhe2048"},
@code{"@@ffdhe3072"}, @code{"@@ffdhe4096"}, @code{"@@ffdhe6144"} or
@code{"@@ffdhe8192"} to use bundled parameters from RFC 7919.

@item @code{ssl-ciphers} (default: @code{#f})
The @code{ssl-ciphers} option chooses the cipher suites to make available
for use in SSL/TLS.

This option is specified using
@uref{https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT,
OpenSSL cipher list notation}.

It is recommended that you try your cipher string using 'openssl ciphers
<string>' before setting it here, to get a feel for which cipher suites you
will get.  After setting this option, it is recommend that you inspect your
Murmur log to ensure that Murmur is using the cipher suites that you
expected it to.

Note: Changing this option may impact the backwards compatibility of your
Murmur server, and can remove the ability for older Mumble clients to be
able to connect to it.

@item @code{public-registration} (default: @code{#f})
Must be a @code{<murmur-public-registration-configuration>} record or
@code{#f}.

You can optionally register your server in the public server list that the
@code{mumble} client shows on startup.  You cannot register your server if
you have set a @code{server-password}, or set @code{allow-ping} to
@code{#f}.

It might take a few hours until it shows up in the public list.

@item @code{file} (default: @code{#f})
Optional alternative override for this configuration.
@end table
@end deftp

@deftp {Data Type} murmur-public-registration-configuration
Configuration for public registration of a murmur service.

@table @asis
@item @code{name}
This is a display name for your server. Not to be confused with the
hostname.

@item @code{password}
A password to identify your registration.  Subsequent updates will need the
same password. Don't lose your password.

@item @code{url}
This should be a @code{http://} or @code{https://} link to your web site.

@item @code{hostname} (default: @code{#f})
By default your server will be listed by its IP address.  If it is set your
server will be linked by this host name instead.
@end table
@end deftp



@node Überwachungsdienste
@subsubsection Überwachungsdienste

@subsubheading Tailon Service

@uref{https://tailon.readthedocs.io/, Tailon} is a web application for
viewing and searching log files.

The following example will configure the service with default values.  By
default, Tailon can be accessed on port 8080 (@code{http://localhost:8080}).

@example
(service tailon-service-type)
@end example

The following example customises more of the Tailon configuration, adding
@command{sed} to the list of allowed commands.

@example
(service tailon-service-type
         (tailon-configuration
           (config-file
             (tailon-configuration-file
               (allowed-commands '("tail" "grep" "awk" "sed"))))))
@end example


@deftp {Data Type} tailon-configuration
Data type representing the configuration of Tailon.  This type has the
following parameters:

@table @asis
@item @code{config-file} (default: @code{(tailon-configuration-file)})
The configuration file to use for Tailon. This can be set to a
@dfn{tailon-configuration-file} record value, or any gexp
(@pxref{G-Ausdrücke}).

For example, to instead use a local file, the @code{local-file} function can
be used:

@example
(service tailon-service-type
         (tailon-configuration
           (config-file (local-file "./my-tailon.conf"))))
@end example

@item @code{package} (default: @code{tailon})
The tailon package to use.

@end table
@end deftp

@deftp {Data Type} tailon-configuration-file
Data type representing the configuration options for Tailon.  This type has
the following parameters:

@table @asis
@item @code{files} (default: @code{(list "/var/log")})
List of files to display. The list can include strings for a single file or
directory, or a list, where the first item is the name of a subsection, and
the remaining items are the files or directories in that subsection.

@item @code{bind} (default: @code{"localhost:8080"})
Address and port to which Tailon should bind on.

@item @code{relative-root} (default: @code{#f})
URL path to use for Tailon, set to @code{#f} to not use a path.

@item @code{allow-transfers?} (default: @code{#t})
Allow downloading the log files in the web interface.

@item @code{follow-names?} (default: @code{#t})
Allow tailing of not-yet existent files.

@item @code{tail-lines} (default: @code{200})
Number of lines to read initially from each file.

@item @code{allowed-commands} (default: @code{(list "tail" "grep" "awk")})
Commands to allow running. By default, @code{sed} is disabled.

@item @code{debug?} (default: @code{#f})
Set @code{debug?} to @code{#t} to show debug messages.

@item @code{wrap-lines} (default: @code{#t})
Initial line wrapping state in the web interface. Set to @code{#t} to
initially wrap lines (the default), or to @code{#f} to initially not wrap
lines.

@item @code{http-auth} (default: @code{#f})
HTTP authentication type to use. Set to @code{#f} to disable authentication
(the default). Supported values are @code{"digest"} or @code{"basic"}.

@item @code{users} (default: @code{#f})
If HTTP authentication is enabled (see @code{http-auth}), access will be
restricted to the credentials provided here. To configure users, use a list
of pairs, where the first element of the pair is the username, and the 2nd
element of the pair is the password.

@example
(tailon-configuration-file
  (http-auth "basic")
  (users     '(("user1" . "password1")
               ("user2" . "password2"))))
@end example

@end table
@end deftp


@subsubheading Darkstat Service
@cindex darkstat
Darkstat is a packet sniffer that captures network traffic, calculates
statistics about usage, and serves reports over HTTP.

@defvar {Scheme Variable} darkstat-service-type
This is the service type for the @uref{https://unix4lyfe.org/darkstat/,
darkstat} service, its value must be a @code{darkstat-configuration} record
as in this example:

@example
(service darkstat-service-type
         (darkstat-configuration
           (interface "eno1")))
@end example
@end defvar

@deftp {Data Type} darkstat-configuration
Data type representing the configuration of @command{darkstat}.

@table @asis
@item @code{package} (default: @code{darkstat})
The darkstat package to use.

@item @code{interface}
Capture traffic on the specified network interface.

@item @code{port} (default: @code{"667"})
Bind the web interface to the specified port.

@item @code{bind-address} (default: @code{"127.0.0.1"})
Bind the web interface to the specified address.

@item @code{base} (default: @code{"/"})
Specify the path of the base URL.  This can be useful if @command{darkstat}
is accessed via a reverse proxy.

@end table
@end deftp

@subsubheading Prometheus Node Exporter Service

@cindex prometheus-node-exporter
The Prometheus ``node exporter'' makes hardware and operating system
statistics provided by the Linux kernel available for the Prometheus
monitoring system.  This service should be deployed on all physical nodes
and virtual machines, where monitoring these statistics is desirable.

@defvar {Scheme variable} prometheus-node-exporter-service-type
This is the service type for the
@uref{https://github.com/prometheus/node_exporter/,
prometheus-node-exporter} service, its value must be a
@code{prometheus-node-exporter-configuration} record as in this example:

@example
(service prometheus-node-exporter-service-type
         (prometheus-node-exporter-configuration
           (web-listen-address ":9100")))
@end example
@end defvar

@deftp {Data Type} prometheus-node-exporter-configuration
Data type representing the configuration of @command{node_exporter}.

@table @asis
@item @code{package} (default: @code{go-github-com-prometheus-node-exporter})
The prometheus-node-exporter package to use.

@item @code{web-listen-address} (default: @code{":9100"})
Bind the web interface to the specified address.

@end table
@end deftp

@node Kerberos-Dienste
@subsubsection Kerberos-Dienste
@cindex Kerberos

The @code{(gnu services kerberos)} module provides services relating to the
authentication protocol @dfn{Kerberos}.

@subsubheading Krb5 Service

Programs using a Kerberos client library normally expect a configuration
file in @file{/etc/krb5.conf}.  This service generates such a file from a
definition provided in the operating system declaration.  It does not cause
any daemon to be started.

No ``keytab'' files are provided by this service---you must explicitly
create them.  This service is known to work with the MIT client library,
@code{mit-krb5}.  Other implementations have not been tested.

@defvr {Scheme Variable} krb5-service-type
A service type for Kerberos 5 clients.
@end defvr

@noindent
Here is an example of its use:
@lisp
(service krb5-service-type
         (krb5-configuration
          (default-realm "EXAMPLE.COM")
          (allow-weak-crypto? #t)
          (realms (list
                   (krb5-realm
                    (name "EXAMPLE.COM")
                    (admin-server "groucho.example.com")
                    (kdc "karl.example.com"))
                   (krb5-realm
                    (name "ARGRX.EDU")
                    (admin-server "kerb-admin.argrx.edu")
                    (kdc "keys.argrx.edu"))))))
@end lisp

@noindent
This example provides a Kerberos@tie{}5 client configuration which:
@itemize
@item Recognizes two realms, @i{viz:} ``EXAMPLE.COM'' and ``ARGRX.EDU'', both
of which have distinct administration servers and key distribution centers;
@item Will default to the realm ``EXAMPLE.COM'' if the realm is not explicitly
specified by clients;
@item Accepts services which only support encryption types known to be weak.
@end itemize

The @code{krb5-realm} and @code{krb5-configuration} types have many fields.
Only the most commonly used ones are described here.  For a full list, and
more detailed explanation of each, see the MIT
@uref{http://web.mit.edu/kerberos/krb5-devel/doc/admin/conf_files/krb5_conf.html,,krb5.conf}
documentation.


@deftp {Data Type} krb5-realm
@cindex realm, kerberos
@table @asis
@item @code{name}
This field is a string identifying the name of the realm.  A common
convention is to use the fully qualified DNS name of your organization,
converted to upper case.

@item @code{admin-server}
This field is a string identifying the host where the administration server
is running.

@item @code{kdc}
This field is a string identifying the key distribution center for the
realm.
@end table
@end deftp

@deftp {Data Type} krb5-configuration

@table @asis
@item @code{allow-weak-crypto?} (default: @code{#f})
If this flag is @code{#t} then services which only offer encryption
algorithms known to be weak will be accepted.

@item @code{default-realm} (default: @code{#f})
This field should be a string identifying the default Kerberos realm for the
client.  You should set this field to the name of your Kerberos realm.  If
this value is @code{#f} then a realm must be specified with every Kerberos
principal when invoking programs such as @command{kinit}.

@item @code{realms}
This should be a non-empty list of @code{krb5-realm} objects, which clients
may access.  Normally, one of them will have a @code{name} field matching
the @code{default-realm} field.
@end table
@end deftp


@subsubheading PAM krb5 Service
@cindex pam-krb5

The @code{pam-krb5} service allows for login authentication and password
management via Kerberos.  You will need this service if you want PAM enabled
applications to authenticate users using Kerberos.

@defvr {Scheme Variable} pam-krb5-service-type
A service type for the Kerberos 5 PAM module.
@end defvr

@deftp {Data Type} pam-krb5-configuration
Data type representing the configuration of the Kerberos 5 PAM module This
type has the following parameters:
@table @asis
@item @code{pam-krb5} (default: @code{pam-krb5})
The pam-krb5 package to use.

@item @code{minimum-uid} (default: @code{1000})
The smallest user ID for which Kerberos authentications should be
attempted.  Local accounts with lower values will silently fail to
authenticate.
@end table
@end deftp


@node Web-Dienste
@subsubsection Web-Dienste

@cindex web
@cindex www
@cindex HTTP
The @code{(gnu services web)} module provides the Apache HTTP Server, the
nginx web server, and also a fastcgi wrapper daemon.

@subsubheading Apache HTTP Server

@deffn {Scheme Variable} httpd-service-type
Service type for the @uref{https://httpd.apache.org/,Apache HTTP} server
(@dfn{httpd}).  The value for this service type is a
@code{https-configuration} record.

A simple example configuration is given below.

@example
(service httpd-service-type
         (httpd-configuration
           (config
             (httpd-config-file
               (server-name "www.example.com")
               (document-root "/srv/http/www.example.com")))))
@end example

Other services can also extend the @code{httpd-service-type} to add to the
configuration.

@example
(simple-service 'my-extra-server httpd-service-type
                (list
                  (httpd-virtualhost
                    "*:80"
                    (list (string-append
                           "ServerName "www.example.com
                            DocumentRoot \"/srv/http/www.example.com\"")))))
@end example
@end deffn

The details for the @code{httpd-configuration}, @code{httpd-module},
@code{httpd-config-file} and @code{httpd-virtualhost} record types are given
below.

@deffn {Data Type} httpd-configuration
This data type represents the configuration for the httpd service.

@table @asis
@item @code{package} (default: @code{httpd})
The httpd package to use.

@item @code{pid-file} (default: @code{"/var/run/httpd"})
The pid file used by the shepherd-service.

@item @code{config} (default: @code{(httpd-config-file)})
The configuration file to use with the httpd service. The default value is a
@code{httpd-config-file} record, but this can also be a different
G-expression that generates a file, for example a @code{plain-file}. A file
outside of the store can also be specified through a string.

@end table
@end deffn

@deffn {Data Type} httpd-module
This data type represents a module for the httpd service.

@table @asis
@item @code{name}
The name of the module.

@item @code{file}
The file for the module. This can be relative to the httpd package being
used, the absolute location of a file, or a G-expression for a file within
the store, for example @code{(file-append mod-wsgi "/modules/mod_wsgi.so")}.

@end table
@end deffn

@defvr {Scheme Variable} %default-httpd-modules
A default list of @code{httpd-module} objects.
@end defvr

@deffn {Data Type} httpd-config-file
This data type represents a configuration file for the httpd service.

@table @asis
@item @code{modules} (default: @code{%default-httpd-modules})
The modules to load. Additional modules can be added here, or loaded by
additional configuration.

For example, in order to handle requests for PHP files, you can use Apache’s
@code{mod_proxy_fcgi} module along with @code{php-fpm-service-type}:

@example
(service httpd-service-type
         (httpd-configuration
          (config
           (httpd-config-file
            (modules (cons*
                      (httpd-module
                       (name "proxy_module")
                       (file "modules/mod_proxy.so"))
                      (httpd-module
                       (name "proxy_fcgi_module")
                       (file "modules/mod_proxy_fcgi.so"))
                      %default-httpd-modules))
            (extra-config (list "\
<FilesMatch \\.php$>
    SetHandler \"proxy:unix:/var/run/php-fpm.sock|fcgi://localhost/\"
</FilesMatch>"))))))
(service php-fpm-service-type
         (php-fpm-configuration
          (socket "/var/run/php-fpm.sock")
          (socket-group "httpd")))
@end example

@item @code{server-root} (default: @code{httpd})
The @code{ServerRoot} in the configuration file, defaults to the httpd
package. Directives including @code{Include} and @code{LoadModule} are taken
as relative to the server root.

@item @code{server-name} (default: @code{#f})
The @code{ServerName} in the configuration file, used to specify the request
scheme, hostname and port that the server uses to identify itself.

This doesn't need to be set in the server config, and can be specifyed in
virtual hosts. The default is @code{#f} to not specify a @code{ServerName}.

@item @code{document-root} (default: @code{"/srv/http"})
The @code{DocumentRoot} from which files will be served.

@item @code{listen} (default: @code{'("80")})
The list of values for the @code{Listen} directives in the config file. The
value should be a list of strings, when each string can specify the port
number to listen on, and optionally the IP address and protocol to use.

@item @code{pid-file} (default: @code{"/var/run/httpd"})
The @code{PidFile} to use. This should match the @code{pid-file} set in the
@code{httpd-configuration} so that the Shepherd service is configured
correctly.

@item @code{error-log} (default: @code{"/var/log/httpd/error_log"})
The @code{ErrorLog} to which the server will log errors.

@item @code{user} (default: @code{"httpd"})
The @code{User} which the server will answer requests as.

@item @code{group} (default: @code{"httpd"})
The @code{Group} which the server will answer requests as.

@item @code{extra-config} (default: @code{(list "TypesConfig etc/httpd/mime.types")})
A flat list of strings and G-expressions which will be added to the end of
the configuration file.

Any values which the service is extended with will be appended to this list.

@end table
@end deffn

@deffn {Data Type} httpd-virtualhost
This data type represents a virtualhost configuration block for the httpd
service.

These should be added to the extra-config for the httpd-service.

@example
(simple-service 'my-extra-server httpd-service-type
                (list
                  (httpd-virtualhost
                    "*:80"
                    (list (string-append
                           "ServerName "www.example.com
                            DocumentRoot \"/srv/http/www.example.com\"")))))
@end example

@table @asis
@item @code{addresses-and-ports}
The addresses and ports for the @code{VirtualHost} directive.

@item @code{contents}
The contents of the @code{VirtualHost} directive, this should be a list of
strings and G-expressions.

@end table
@end deffn

@subsubheading NGINX

@deffn {Scheme Variable} nginx-service-type
Service type for the @uref{https://nginx.org/,NGinx} web server.  The value
for this service type is a @code{<nginx-configuration>} record.

A simple example configuration is given below.

@example
(service nginx-service-type
         (nginx-configuration
           (server-blocks
             (list (nginx-server-configuration
                     (server-name '("www.example.com"))
                     (root "/srv/http/www.example.com"))))))
@end example

In addition to adding server blocks to the service configuration directly,
this service can be extended by other services to add server blocks, as in
this example:

@example
(simple-service 'my-extra-server nginx-service-type
                (list (nginx-server-configuration
                        (root "/srv/http/extra-website")
                        (try-files (list "$uri" "$uri/index.html")))))
@end example
@end deffn

At startup, @command{nginx} has not yet read its configuration file, so it
uses a default file to log error messages.  If it fails to load its
configuration file, that is where error messages are logged.  After the
configuration file is loaded, the default error log file changes as per
configuration.  In our case, startup error messages can be found in
@file{/var/run/nginx/logs/error.log}, and after configuration in
@file{/var/log/nginx/error.log}.  The second location can be changed with
the @var{log-directory} configuration option.

@deffn {Data Type} nginx-configuration
This data type represents the configuration for NGinx. Some configuration
can be done through this and the other provided record types, or
alternatively, a config file can be provided.

@table @asis
@item @code{nginx} (default: @code{nginx})
The nginx package to use.

@item @code{log-directory} (default: @code{"/var/log/nginx"})
The directory to which NGinx will write log files.

@item @code{run-directory} (default: @code{"/var/run/nginx"})
The directory in which NGinx will create a pid file, and write temporary
files.

@item @code{server-blocks} (default: @code{'()})
A list of @dfn{server blocks} to create in the generated configuration file,
the elements should be of type @code{<nginx-server-configuration>}.

The following example would setup NGinx to serve @code{www.example.com} from
the @code{/srv/http/www.example.com} directory, without using HTTPS.
@example
(service nginx-service-type
         (nginx-configuration
           (server-blocks
             (list (nginx-server-configuration
                     (server-name '("www.example.com"))
                     (root "/srv/http/www.example.com"))))))
@end example

@item @code{upstream-blocks} (default: @code{'()})
A list of @dfn{upstream blocks} to create in the generated configuration
file, the elements should be of type @code{<nginx-upstream-configuration>}.

Configuring upstreams through the @code{upstream-blocks} can be useful when
combined with @code{locations} in the @code{<nginx-server-configuration>}
records.  The following example creates a server configuration with one
location configuration, that will proxy requests to a upstream
configuration, which will handle requests with two servers.

@example
(service
  nginx-service-type
  (nginx-configuration
    (server-blocks
      (list (nginx-server-configuration
              (server-name '("www.example.com"))
              (root "/srv/http/www.example.com")
              (locations
                (list
                  (nginx-location-configuration
                  (uri "/path1")
                  (body '("proxy_pass http://server-proxy;"))))))))
    (upstream-blocks
      (list (nginx-upstream-configuration
              (name "server-proxy")
              (servers (list "server1.example.com"
                             "server2.example.com")))))))
@end example

@item @code{file} (default: @code{#f})
If a configuration @var{file} is provided, this will be used, rather than
generating a configuration file from the provided @code{log-directory},
@code{run-directory}, @code{server-blocks} and @code{upstream-blocks}.  For
proper operation, these arguments should match what is in @var{file} to
ensure that the directories are created when the service is activated.

This can be useful if you have an existing configuration file, or it's not
possible to do what is required through the other parts of the
nginx-configuration record.

@item @code{server-names-hash-bucket-size} (default: @code{#f})
Bucket size for the server names hash tables, defaults to @code{#f} to use
the size of the processors cache line.

@item @code{server-names-hash-bucket-max-size} (default: @code{#f})
Maximum bucket size for the server names hash tables.

@item @code{extra-content} (default: @code{""})
Extra content for the @code{http} block.  Should be string or a string
valued G-expression.

@end table
@end deffn

@deftp {Data Type} nginx-server-configuration
Data type representing the configuration of an nginx server block.  This
type has the following parameters:

@table @asis
@item @code{listen} (default: @code{'("80" "443 ssl")})
Each @code{listen} directive sets the address and port for IP, or the path
for a UNIX-domain socket on which the server will accept requests.  Both
address and port, or only address or only port can be specified.  An address
may also be a hostname, for example:

@example
'("127.0.0.1:8000" "127.0.0.1" "8000" "*:8000" "localhost:8000")
@end example

@item @code{server-name} (default: @code{(list 'default)})
A list of server names this server represents. @code{'default} represents
the default server for connections matching no other server.

@item @code{root} (default: @code{"/srv/http"})
Root of the website nginx will serve.

@item @code{locations} (default: @code{'()})
A list of @dfn{nginx-location-configuration} or
@dfn{nginx-named-location-configuration} records to use within this server
block.

@item @code{index} (default: @code{(list "index.html")})
Index files to look for when clients ask for a directory.  If it cannot be
found, Nginx will send the list of files in the directory.

@item @code{try-files} (default: @code{'()})
A list of files whose existence is checked in the specified order.
@code{nginx} will use the first file it finds to process the request.

@item @code{ssl-certificate} (default: @code{#f})
Where to find the certificate for secure connections.  Set it to @code{#f}
if you don't have a certificate or you don't want to use HTTPS.

@item @code{ssl-certificate-key} (default: @code{#f})
Where to find the private key for secure connections.  Set it to @code{#f}
if you don't have a key or you don't want to use HTTPS.

@item @code{server-tokens?} (default: @code{#f})
Whether the server should add its configuration to response.

@item @code{raw-content} (default: @code{'()})
A list of raw lines added to the server block.

@end table
@end deftp

@deftp {Data Type} nginx-upstream-configuration
Data type representing the configuration of an nginx @code{upstream} block.
This type has the following parameters:

@table @asis
@item @code{name}
Name for this group of servers.

@item @code{servers}
Specify the addresses of the servers in the group.  The address can be
specified as a IP address (e.g. @samp{127.0.0.1}), domain name
(e.g. @samp{backend1.example.com}) or a path to a UNIX socket using the
prefix @samp{unix:}.  For addresses using an IP address or domain name, the
default port is 80, and a different port can be specified explicitly.

@end table
@end deftp

@deftp {Data Type} nginx-location-configuration
Data type representing the configuration of an nginx @code{location} block.
This type has the following parameters:

@table @asis
@item @code{uri}
URI which this location block matches.

@anchor{nginx-location-configuration body}
@item @code{body}
Body of the location block, specified as a list of strings. This can contain
many configuration directives.  For example, to pass requests to a upstream
server group defined using an @code{nginx-upstream-configuration} block, the
following directive would be specified in the body @samp{(list "proxy_pass
http://upstream-name;")}.

@end table
@end deftp

@deftp {Data Type} nginx-named-location-configuration
Data type representing the configuration of an nginx named location block.
Named location blocks are used for request redirection, and not used for
regular request processing.  This type has the following parameters:

@table @asis
@item @code{name}
Name to identify this location block.

@item @code{body}
@xref{nginx-location-configuration body}, as the body for named location
blocks can be used in a similar way to the
@code{nginx-location-configuration body}.  One restriction is that the body
of a named location block cannot contain location blocks.

@end table
@end deftp

@subsubheading Varnish Cache
@cindex Varnish
Varnish is a fast cache server that sits in between web applications and end
users.  It proxies requests from clients and caches the accessed URLs such
that multiple requests for the same resource only creates one request to the
back-end.

@defvr {Scheme Variable} varnish-service-type
Service type for the Varnish daemon.
@end defvr

@deftp {Data Type} varnish-configuration
Data type representing the @code{varnish} service configuration.  This type
has the following parameters:

@table @asis
@item @code{package} (default: @code{varnish})
The Varnish package to use.

@item @code{name} (default: @code{"default"})
A name for this Varnish instance.  Varnish will create a directory in
@file{/var/varnish/} with this name and keep temporary files there.  If the
name starts with a forward slash, it is interpreted as an absolute directory
name.

Pass the @code{-n} argument to other Varnish programs to connect to the
named instance, e.g. @command{varnishncsa -n default}.

@item @code{backend} (default: @code{"localhost:8080"})
The backend to use.  This option has no effect if @code{vcl} is set.

@item @code{vcl} (default: #f)
The @dfn{VCL} (Varnish Configuration Language) program to run.  If this is
@code{#f}, Varnish will proxy @code{backend} using the default
configuration.  Otherwise this must be a file-like object with valid VCL
syntax.

@c Varnish does not support HTTPS, so keep this URL to avoid confusion.
For example, to mirror @url{http://www.gnu.org,www.gnu.org} with VCL you can
do something along these lines:

@example
(define %gnu-mirror
  (plain-file
   "gnu.vcl"
   "vcl 4.1;
backend gnu @{ .host = "www.gnu.org"; @}"))

(operating-system
  ...
  (services (cons (service varnish-service-type
                           (varnish-configuration
                            (listen '(":80"))
                            (vcl %gnu-mirror)))
                  %base-services)))
@end example

The configuration of an already running Varnish instance can be inspected
and changed using the @command{varnishadm} program.

Consult the @url{https://varnish-cache.org/docs/,Varnish User Guide} and
@url{https://book.varnish-software.com/4.0/,Varnish Book} for comprehensive
documentation on Varnish and its configuration language.

@item @code{listen} (default: @code{'("localhost:80")})
List of addresses Varnish will listen on.

@item @code{storage} (default: @code{'("malloc,128m")})
List of storage backends that will be available in VCL.

@item @code{parameters} (default: @code{'()})
List of run-time parameters in the form @code{'(("parameter" . "value"))}.

@item @code{extra-options} (default: @code{'()})
Additional arguments to pass to the @command{varnishd} process.

@end table
@end deftp

@subsubheading FastCGI
@cindex fastcgi
@cindex fcgiwrap
FastCGI is an interface between the front-end and the back-end of a web
service.  It is a somewhat legacy facility; new web services should
generally just talk HTTP between the front-end and the back-end.  However
there are a number of back-end services such as PHP or the optimized HTTP
Git repository access that use FastCGI, so we have support for it in Guix.

To use FastCGI, you configure the front-end web server (e.g., nginx) to
dispatch some subset of its requests to the fastcgi backend, which listens
on a local TCP or UNIX socket.  There is an intermediary @code{fcgiwrap}
program that sits between the actual backend process and the web server.
The front-end indicates which backend program to run, passing that
information to the @code{fcgiwrap} process.

@defvr {Scheme Variable} fcgiwrap-service-type
A service type for the @code{fcgiwrap} FastCGI proxy.
@end defvr

@deftp {Data Type} fcgiwrap-configuration
Data type representing the configuration of the @code{fcgiwrap} serice.
This type has the following parameters:
@table @asis
@item @code{package} (default: @code{fcgiwrap})
The fcgiwrap package to use.

@item @code{socket} (default: @code{tcp:127.0.0.1:9000})
The socket on which the @code{fcgiwrap} process should listen, as a string.
Valid @var{socket} values include @code{unix:@var{/path/to/unix/socket}},
@code{tcp:@var{dot.ted.qu.ad}:@var{port}} and
@code{tcp6:[@var{ipv6_addr}]:port}.

@item @code{user} (default: @code{fcgiwrap})
@itemx @code{group} (default: @code{fcgiwrap})
The user and group names, as strings, under which to run the @code{fcgiwrap}
process.  The @code{fastcgi} service will ensure that if the user asks for
the specific user or group names @code{fcgiwrap} that the corresponding user
and/or group is present on the system.

It is possible to configure a FastCGI-backed web service to pass HTTP
authentication information from the front-end to the back-end, and to allow
@code{fcgiwrap} to run the back-end process as a corresponding local user.
To enable this capability on the back-end., run @code{fcgiwrap} as the
@code{root} user and group.  Note that this capability also has to be
configured on the front-end as well.
@end table
@end deftp

@cindex php-fpm
PHP-FPM (FastCGI Process Manager) is an alternative PHP FastCGI
implementation with some additional features useful for sites of any size.

These features include:
@itemize @bullet
@item Adaptive process spawning
@item Basic statistics (similar to Apache's mod_status)
@item Advanced process management with graceful stop/start
@item Ability to start workers with different uid/gid/chroot/environment
and different php.ini (replaces safe_mode)
@item Stdout & stderr logging
@item Emergency restart in case of accidental opcode cache destruction
@item Accelerated upload support
@item Support for a "slowlog"
@item Enhancements to FastCGI, such as fastcgi_finish_request() -
a special function to finish request & flush all data while continuing to do
something time-consuming (video converting, stats processing, etc.)
@end itemize
... and much more.

@defvr {Scheme Variable} php-fpm-service-type
A Service type for @code{php-fpm}.
@end defvr

@deftp {Data Type} php-fpm-configuration
Data Type for php-fpm service configuration.
@table @asis
@item @code{php} (default: @code{php})
The php package to use.
@item @code{socket} (default: @code{(string-append "/var/run/php" (version-major (package-version php)) "-fpm.sock")})
The address on which to accept FastCGI requests.  Valid syntaxes are:
@table @asis
@item @code{"ip.add.re.ss:port"}
Listen on a TCP socket to a specific address on a specific port.
@item @code{"port"}
Listen on a TCP socket to all addresses on a specific port.
@item @code{"/path/to/unix/socket"}
Listen on a unix socket.
@end table

@item @code{user} (default: @code{php-fpm})
User who will own the php worker processes.
@item @code{group} (default: @code{php-fpm})
Group of the worker processes.
@item @code{socket-user} (default: @code{php-fpm})
User who can speak to the php-fpm socket.
@item @code{socket-group} (default: @code{php-fpm})
Group that can speak to the php-fpm socket.
@item @code{pid-file} (default: @code{(string-append "/var/run/php" (version-major (package-version php)) "-fpm.pid")})
The process id of the php-fpm process is written to this file once the
service has started.
@item @code{log-file} (default: @code{(string-append "/var/log/php" (version-major (package-version php)) "-fpm.log")})
Log for the php-fpm master process.
@item @code{process-manager} (default: @code{(php-fpm-dynamic-process-manager-configuration)})
Detailed settings for the php-fpm process manager.  Must be either:
@table @asis
@item @code{<php-fpm-dynamic-process-manager-configuration>}
@item @code{<php-fpm-static-process-manager-configuration>}
@item @code{<php-fpm-on-demand-process-manager-configuration>}
@end table
@item @code{display-errors} (default @code{#f})
Determines whether php errors and warning should be sent to clients and
displayed in their browsers.  This is useful for local php development, but
a security risk for public sites, as error messages can reveal passwords and
personal data.
@item @code{workers-logfile} (default @code{(string-append "/var/log/php" (version-major (package-version php)) "-fpm.www.log")})
This file will log the @code{stderr} outputs of php worker processes.  Can
be set to @code{#f} to disable logging.
@item @code{file} (default @code{#f})
An optional override of the whole configuration.  You can use the
@code{mixed-text-file} function or an absolute filepath for it.
@end table
@end deftp

@deftp {Data type} php-fpm-dynamic-process-manager-configuration
Data Type for the @code{dynamic} php-fpm process manager.  With the
@code{dynamic} process manager, spare worker processes are kept around based
on it's configured limits.
@table @asis
@item @code{max-children} (default: @code{5})
Maximum of worker processes.
@item @code{start-servers} (default: @code{2})
How many worker processes should be started on start-up.
@item @code{min-spare-servers} (default: @code{1})
How many spare worker processes should be kept around at minimum.
@item @code{max-spare-servers} (default: @code{3})
How many spare worker processes should be kept around at maximum.
@end table
@end deftp

@deftp {Data type} php-fpm-static-process-manager-configuration
Data Type for the @code{static} php-fpm process manager.  With the
@code{static} process manager, an unchanging number of worker processes are
created.
@table @asis
@item @code{max-children} (default: @code{5})
Maximum of worker processes.
@end table
@end deftp

@deftp {Data type} php-fpm-on-demand-process-manager-configuration
Data Type for the @code{on-demand} php-fpm process manager.  With the
@code{on-demand} process manager, worker processes are only created as
requests arrive.
@table @asis
@item @code{max-children} (default: @code{5})
Maximum of worker processes.
@item @code{process-idle-timeout} (default: @code{10})
The time in seconds after which a process with no requests is killed.
@end table
@end deftp


@deffn {Scheme Procedure} nginx-php-fpm-location @
       [#:nginx-package nginx] @ [socket (string-append "/var/run/php" @
(version-major (package-version php)) @ "-fpm.sock")] A helper function to
quickly add php to an @code{nginx-server-configuration}.
@end deffn

A simple services setup for nginx with php can look like this:
@example
(services (cons* (service dhcp-client-service-type)
                 (service php-fpm-service-type)
                 (service nginx-service-type
                          (nginx-server-configuration
                           (server-name '("example.com"))
                           (root "/srv/http/")
                           (locations
                            (list (nginx-php-location)))
                           (https-port #f)
                           (ssl-certificate #f)
                           (ssl-certificate-key #f)))
                 %base-services))
@end example

@cindex cat-avatar-generator
The cat avatar generator is a simple service to demonstrate the use of
php-fpm in @code{Nginx}.  It is used to generate cat avatar from a seed, for
instance the hash of a user's email address.

@deffn {Scheme Procedure} cat-avatar-generator-serice @
       [#:cache-dir "/var/cache/cat-avatar-generator"] @ [#:package
cat-avatar-generator] @ [#:configuration (nginx-server-configuration)]
Returns an nginx-server-configuration that inherits @code{configuration}.
It extends the nginx configuration to add a server block that serves
@code{package}, a version of cat-avatar-generator.  During execution,
cat-avatar-generator will be able to use @code{cache-dir} as its cache
directory.
@end deffn

A simple setup for cat-avatar-generator can look like this:
@example
(services (cons* (cat-avatar-generator-service
                  #:configuration
                  (nginx-server-configuration
                    (server-name '("example.com"))))
                 ...
                 %base-services))
@end example

@subsubheading Hpcguix-web

@cindex hpcguix-web
The @uref{hpcguix-web, https://github.com/UMCUGenetics/hpcguix-web/} program
is a customizable web interface to browse Guix packages, initially designed
for users of high-performance computing (HPC)  clusters.

@defvr {Scheme Variable} hpcguix-web-service-type
The service type for @code{hpcguix-web}.
@end defvr

@deftp {Data Type} hpcguix-web-configuration
Data type for the hpcguix-web service configuration.

@table @asis
@item @code{specs}
A gexp (@pxref{G-Ausdrücke}) specifying the hpcguix-web service
configuration.  The main items available in this spec are:

@table @asis
@item @code{title-prefix} (default: @code{"hpcguix | "})
The page title prefix.

@item @code{guix-command} (default: @code{"guix"})
The @command{guix} command.

@item @code{package-filter-proc} (default: @code{(const #t)})
A procedure specifying how to filter packages that are displayed.

@item @code{package-page-extension-proc} (default: @code{(const '())})
Extension package for @code{hpcguix-web}.

@item @code{menu} (default: @code{'()})
Additional entry in page @code{menu}.

@item @code{channels} (default: @code{%default-channels})
List of channels from which the package list is built (@pxref{Channels}).

@item @code{package-list-expiration} (default: @code{(* 12 3600)})
The expiration time, in seconds, after which the package list is rebuilt
from the latest instances of the given channels.
@end table

See the hpcguix-web repository for a
@uref{https://github.com/UMCUGenetics/hpcguix-web/blob/master/hpcweb-configuration.scm,
complete example}.

@item @code{package} (default: @code{hpcguix-web})
The hpcguix-web package to use.
@end table
@end deftp

A typical hpcguix-web service declaration looks like this:

@example
(service hpcguix-web-service-type
         (hpcguix-web-configuration
          (specs
           #~(define site-config
               (hpcweb-configuration
                (title-prefix "Guix-HPC - ")
                (menu '(("/about" "ABOUT"))))))))
@end example

@quotation Anmerkung
The hpcguix-web service periodically updates the package list it publishes
by pulling channels from Git.  To that end, it needs to access X.509
certificates so that it can authenticate Git servers when communicating over
HTTPS, and it assumes that @file{/etc/ssl/certs} contains those
certificates.

Thus, make sure to add @code{nss-certs} or another certificate package to
the @code{packages} field of your configuration.  @ref{X.509-Zertifikate},
for more information on X.509 certificates.
@end quotation

@node Zertifikatsdienste
@subsubsection Zertifikatsdienste

@cindex Web
@cindex HTTP, HTTPS
@cindex Let's Encrypt
@cindex TLS certificates
The @code{(gnu services certbot)} module provides a service to automatically
obtain a valid TLS certificate from the Let's Encrypt certificate
authority.  These certificates can then be used to serve content securely
over HTTPS or other TLS-based protocols, with the knowledge that the client
will be able to verify the server's authenticity.

@url{https://letsencrypt.org/, Let's Encrypt} provides the @code{certbot}
tool to automate the certification process.  This tool first securely
generates a key on the server.  It then makes a request to the Let's Encrypt
certificate authority (CA) to sign the key.  The CA checks that the request
originates from the host in question by using a challenge-response protocol,
requiring the server to provide its response over HTTP.  If that protocol
completes successfully, the CA signs the key, resulting in a certificate.
That certificate is valid for a limited period of time, and therefore to
continue to provide TLS services, the server needs to periodically ask the
CA to renew its signature.

The certbot service automates this process: the initial key generation, the
initial certification request to the Let's Encrypt service, the web server
challenge/response integration, writing the certificate to disk, the
automated periodic renewals, and the deployment tasks associated with the
renewal (e.g. reloading services, copying keys with different permissions).

Certbot is run twice a day, at a random minute within the hour.  It won't do
anything until your certificates are due for renewal or revoked, but running
it regularly would give your service a chance of staying online in case a
Let's Encrypt-initiated revocation happened for some reason.

By using this service, you agree to the ACME Subscriber Agreement, which can
be found there: @url{https://acme-v01.api.letsencrypt.org/directory}.

@defvr {Scheme Variable} certbot-service-type
A service type for the @code{certbot} Let's Encrypt client.  Its value must
be a @code{certbot-configuration} record as in this example:

@example
(define %nginx-deploy-hook
  (program-file
   "nginx-deploy-hook"
   #~(let ((pid (call-with-input-file "/var/run/nginx/pid" read)))
       (kill pid SIGHUP))))

(service certbot-service-type
         (certbot-configuration
          (email "foo@@example.net")
          (certificates
           (list
            (certificate-configuration
             (domains '("example.net" "www.example.net"))
             (deploy-hook %nginx-deploy-hook))
            (certificate-configuration
             (domains '("bar.example.net")))))))
@end example

See below for details about @code{certbot-configuration}.
@end defvr

@deftp {Data Type} certbot-configuration
Data type representing the configuration of the @code{certbot} service.
This type has the following parameters:

@table @asis
@item @code{package} (default: @code{certbot})
The certbot package to use.

@item @code{webroot} (default: @code{/var/www})
The directory from which to serve the Let's Encrypt challenge/response
files.

@item @code{certificates} (default: @code{()})
A list of @code{certificates-configuration}s for which to generate
certificates and request signatures.  Each certificate has a @code{name} and
several @code{domains}.

@item @code{email}
Mandatory email used for registration, recovery contact, and important
account notifications.

@item @code{rsa-key-size} (default: @code{2048})
Size of the RSA key.

@item @code{default-location} (default: @i{see below})
The default @code{nginx-location-configuration}.  Because @code{certbot}
needs to be able to serve challenges and responses, it needs to be able to
run a web server.  It does so by extending the @code{nginx} web service with
an @code{nginx-server-configuration} listening on the @var{domains} on port
80, and which has a @code{nginx-location-configuration} for the
@code{/.well-known/} URI path subspace used by Let's Encrypt.  @xref{Web-Dienste}, for more on these nginx configuration data types.

Requests to other URL paths will be matched by the @code{default-location},
which if present is added to all @code{nginx-server-configuration}s.

By default, the @code{default-location} will issue a redirect from
@code{http://@var{domain}/...} to @code{https://@var{domain}/...}, leaving
you to define what to serve on your site via @code{https}.

Pass @code{#f} to not issue a default location.
@end table
@end deftp

@deftp {Data Type} certificate-configuration
Data type representing the configuration of a certificate.  This type has
the following parameters:

@table @asis
@item @code{name} (default: @i{see below})
This name is used by Certbot for housekeeping and in file paths; it doesn't
affect the content of the certificate itself.  To see certificate names, run
@code{certbot certificates}.

Its default is the first provided domain.

@item @code{domains} (default: @code{()})
The first domain provided will be the subject CN of the certificate, and all
domains will be Subject Alternative Names on the certificate.

@item @code{deploy-hook} (default: @code{#f})
Command to be run in a shell once for each successfully issued certificate.
For this command, the shell variable @code{$RENEWED_LINEAGE} will point to
the config live subdirectory (for example,
@samp{"/etc/letsencrypt/live/example.com"}) containing the new certificates
and keys; the shell variable @code{$RENEWED_DOMAINS} will contain a
space-delimited list of renewed certificate domains (for example,
@samp{"example.com www.example.com"}.

@end table
@end deftp

For each @code{certificate-configuration}, the certificate is saved to
@code{/etc/letsencrypt/live/@var{name}/fullchain.pem} and the key is saved
to @code{/etc/letsencrypt/live/@var{name}/privkey.pem}.
@node DNS-Dienste
@subsubsection DNS-Dienste
@cindex DNS (domain name system)
@cindex domain name system (DNS)

The @code{(gnu services dns)} module provides services related to the
@dfn{domain name system} (DNS).  It provides a server service for hosting an
@emph{authoritative} DNS server for multiple zones, slave or master.  This
service uses @uref{https://www.knot-dns.cz/, Knot DNS}.  And also a caching
and forwarding DNS server for the LAN, which uses
@uref{http://www.thekelleys.org.uk/dnsmasq/doc.html, dnsmasq}.

@subsubheading Knot Service

An example configuration of an authoritative server for two zones, one
master and one slave, is:

@lisp
(define-zone-entries example.org.zone
;; Name TTL Class Type Data
  ("@@"  ""  "IN"  "A"  "127.0.0.1")
  ("@@"  ""  "IN"  "NS" "ns")
  ("ns" ""  "IN"  "A"  "127.0.0.1"))

(define master-zone
  (knot-zone-configuration
    (domain "example.org")
    (zone (zone-file
            (origin "example.org")
            (entries example.org.zone)))))

(define slave-zone
  (knot-zone-configuration
    (domain "plop.org")
    (dnssec-policy "default")
    (master (list "plop-master"))))

(define plop-master
  (knot-remote-configuration
    (id "plop-master")
    (address (list "208.76.58.171"))))

(operating-system
  ;; ...
  (services (cons* (service knot-service-type
                     (knot-configuration
                       (remotes (list plop-master))
                       (zones (list master-zone slave-zone))))
                   ;; ...
                   %base-services)))
@end lisp

@deffn {Scheme Variable} knot-service-type
This is the type for the Knot DNS server.

Knot DNS is an authoritative DNS server, meaning that it can serve multiple
zones, that is to say domain names you would buy from a registrar.  This
server is not a resolver, meaning that it can only resolve names for which
it is authoritative.  This server can be configured to serve zones as a
master server or a slave server as a per-zone basis.  Slave zones will get
their data from masters, and will serve it as an authoritative server.  From
the point of view of a resolver, there is no difference between master and
slave.

The following data types are used to configure the Knot DNS server:
@end deffn

@deftp {Data Type} knot-key-configuration
Data type representing a key.  This type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
An identifier for other configuration fields to refer to this key. IDs must
be unique and must not be empty.

@item @code{algorithm} (default: @code{#f})
The algorithm to use.  Choose between @code{#f}, @code{'hmac-md5},
@code{'hmac-sha1}, @code{'hmac-sha224}, @code{'hmac-sha256},
@code{'hmac-sha384} and @code{'hmac-sha512}.

@item @code{secret} (default: @code{""})
The secret key itself.

@end table
@end deftp

@deftp {Data Type} knot-acl-configuration
Data type representing an Access Control List (ACL) configuration.  This
type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
An identifier for ether configuration fields to refer to this key. IDs must
be unique and must not be empty.

@item @code{address} (default: @code{'()})
An ordered list of IP addresses, network subnets, or network ranges
represented with strings.  The query must match one of them.  Empty value
means that address match is not required.

@item @code{key} (default: @code{'()})
An ordered list of references to keys represented with strings.  The string
must match a key ID defined in a @code{knot-key-configuration}.  No key
means that a key is not require to match that ACL.

@item @code{action} (default: @code{'()})
An ordered list of actions that are permitted or forbidden by this ACL.
Possible values are lists of zero or more elements from @code{'transfer},
@code{'notify} and @code{'update}.

@item @code{deny?} (default: @code{#f})
When true, the ACL defines restrictions.  Listed actions are forbidden.
When false, listed actions are allowed.

@end table
@end deftp

@deftp {Data Type} zone-entry
Data type represnting a record entry in a zone file.  This type has the
following parameters:

@table @asis
@item @code{name} (default: @code{"@@"})
The name of the record.  @code{"@@"} refers to the origin of the zone.
Names are relative to the origin of the zone.  For example, in the
@code{example.org} zone, @code{"ns.example.org"} actually refers to
@code{ns.example.org.example.org}.  Names ending with a dot are absolute,
which means that @code{"ns.example.org."} refers to @code{ns.example.org}.

@item @code{ttl} (default: @code{""})
The Time-To-Live (TTL) of this record.  If not set, the default TTL is used.

@item @code{class} (default: @code{"IN"})
The class of the record.  Knot currently supports only @code{"IN"} and
partially @code{"CH"}.

@item @code{type} (default: @code{"A"})
The type of the record.  Common types include A (IPv4 address), AAAA (IPv6
address), NS (Name Server) and MX (Mail eXchange).  Many other types are
defined.

@item @code{data} (default: @code{""})
The data contained in the record.  For instance an IP address associated
with an A record, or a domain name associated with an NS record.  Remember
that domain names are relative to the origin unless they end with a dot.

@end table
@end deftp

@deftp {Data Type} zone-file
Data type representing the content of a zone file.  This type has the
following parameters:

@table @asis
@item @code{entries} (default: @code{'()})
The list of entries.  The SOA record is taken care of, so you don't need to
put it in the list of entries.  This list should probably contain an entry
for your primary authoritative DNS server.  Other than using a list of
entries directly, you can use @code{define-zone-entries} to define a object
containing the list of entries more easily, that you can later pass to the
@code{entries} field of the @code{zone-file}.

@item @code{origin} (default: @code{""})
The name of your zone.  This parameter cannot be empty.

@item @code{ns} (default: @code{"ns"})
The domain of your primary authoritative DNS server.  The name is relative
to the origin, unless it ends with a dot.  It is mandatory that this primary
DNS server corresponds to an NS record in the zone and that it is associated
to an IP address in the list of entries.

@item @code{mail} (default: @code{"hostmaster"})
An email address people can contact you at, as the owner of the zone.  This
is translated as @code{<mail>@@<origin>}.

@item @code{serial} (default: @code{1})
The serial number of the zone.  As this is used to keep track of changes by
both slaves and resolvers, it is mandatory that it @emph{never} decreases.
Always increment it when you make a change in your zone.

@item @code{refresh} (default: @code{(* 2 24 3600)})
The frequency at which slaves will do a zone transfer.  This value is a
number of seconds.  It can be computed by multiplications or with
@code{(string->duration)}.

@item @code{retry} (default: @code{(* 15 60)})
The period after which a slave will retry to contact its master when it
fails to do so a first time.

@item @code{expiry} (default: @code{(* 14 24 3600)})
Default TTL of records.  Existing records are considered correct for at most
this amount of time.  After this period, resolvers will invalidate their
cache and check again that it still exists.

@item @code{nx} (default: @code{3600})
Default TTL of inexistant records.  This delay is usually short because you
want your new domains to reach everyone quickly.

@end table
@end deftp

@deftp {Data Type} knot-remote-configuration
Data type representing a remote configuration.  This type has the following
parameters:

@table @asis
@item @code{id} (default: @code{""})
An identifier for other configuration fields to refer to this remote. IDs
must be unique and must not be empty.

@item @code{address} (default: @code{'()})
An ordered list of destination IP addresses.  Addresses are tried in
sequence.  An optional port can be given with the @@ separator.  For
instance: @code{(list "1.2.3.4" "2.3.4.5@@53")}.  Default port is 53.

@item @code{via} (default: @code{'()})
An ordered list of source IP addresses.  An empty list will have Knot choose
an appropriate source IP.  An optional port can be given with the @@
separator.  The default is to choose at random.

@item @code{key} (default: @code{#f})
A reference to a key, that is a string containing the identifier of a key
defined in a @code{knot-key-configuration} field.

@end table
@end deftp

@deftp {Data Type} knot-keystore-configuration
Data type representing a keystore to hold dnssec keys.  This type has the
following parameters:

@table @asis
@item @code{id} (default: @code{""})
The id of the keystore.  It must not be empty.

@item @code{backend} (default: @code{'pem})
The backend to store the keys in.  Can be @code{'pem} or @code{'pkcs11}.

@item @code{config} (default: @code{"/var/lib/knot/keys/keys"})
The configuration string of the backend.  An example for the PKCS#11 is:
@code{"pkcs11:token=knot;pin-value=1234
/gnu/store/.../lib/pkcs11/libsofthsm2.so"}.  For the pem backend, the string
reprensents a path in the file system.

@end table
@end deftp

@deftp {Data Type} knot-policy-configuration
Data type representing a dnssec policy.  Knot DNS is able to automatically
sign your zones.  It can either generate and manage your keys automatically
or use keys that you generate.

Dnssec is usually implemented using two keys: a Key Signing Key (KSK) that
is used to sign the second, and a Zone Signing Key (ZSK) that is used to
sign the zone.  In order to be trusted, the KSK needs to be present in the
parent zone (usually a top-level domain).  If your registrar supports
dnssec, you will have to send them your KSK's hash so they can add a DS
record in their zone.  This is not automated and need to be done each time
you change your KSK.

The policy also defines the lifetime of keys.  Usually, ZSK can be changed
easily and use weaker cryptographic functions (they use lower parameters) in
order to sign records quickly, so they are changed often.  The KSK however
requires manual interaction with the registrar, so they are changed less
often and use stronger parameters because they sign only one record.

This type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
The id of the policy.  It must not be empty.

@item @code{keystore} (default: @code{"default"})
A reference to a keystore, that is a string containing the identifier of a
keystore defined in a @code{knot-keystore-configuration} field.  The
@code{"default"} identifier means the default keystore (a kasp database that
was setup by this service).

@item @code{manual?} (default: @code{#f})
Whether the key management is manual or automatic.

@item @code{single-type-signing?} (default: @code{#f})
When @code{#t}, use the Single-Type Signing Scheme.

@item @code{algorithm} (default: @code{"ecdsap256sha256"})
An algorithm of signing keys and issued signatures.

@item @code{ksk-size} (default: @code{256})
The length of the KSK.  Note that this value is correct for the default
algorithm, but would be unsecure for other algorithms.

@item @code{zsk-size} (default: @code{256})
The length of the ZSK.  Note that this value is correct for the default
algorithm, but would be unsecure for other algorithms.

@item @code{dnskey-ttl} (default: @code{'default})
The TTL value for DNSKEY records added into zone apex.  The special
@code{'default} value means same as the zone SOA TTL.

@item @code{zsk-lifetime} (default: @code{(* 30 24 3600)})
The period between ZSK publication and the next rollover initiation.

@item @code{propagation-delay} (default: @code{(* 24 3600)})
An extra delay added for each key rollover step.  This value should be high
enough to cover propagation of data from the master server to all slaves.

@item @code{rrsig-lifetime} (default: @code{(* 14 24 3600)})
A validity period of newly issued signatures.

@item @code{rrsig-refresh} (default: @code{(* 7 24 3600)})
A period how long before a signature expiration the signature will be
refreshed.

@item @code{nsec3?} (default: @code{#f})
When @code{#t}, NSEC3 will be used instead of NSEC.

@item @code{nsec3-iterations} (default: @code{5})
The number of additional times the hashing is performed.

@item @code{nsec3-salt-length} (default: @code{8})
The length of a salt field in octets, which is appended to the original
owner name before hashing.

@item @code{nsec3-salt-lifetime} (default: @code{(* 30 24 3600)})
The validity period of newly issued salt field.

@end table
@end deftp

@deftp {Data Type} knot-zone-configuration
Data type representing a zone served by Knot.  This type has the following
parameters:

@table @asis
@item @code{domain} (default: @code{""})
The domain served by this configuration.  It must not be empty.

@item @code{file} (default: @code{""})
The file where this zone is saved.  This parameter is ignored by master
zones.  Empty means default location that depends on the domain name.

@item @code{zone} (default: @code{(zone-file)})
The content of the zone file.  This parameter is ignored by slave zones.  It
must contain a zone-file record.

@item @code{master} (default: @code{'()})
A list of master remotes.  When empty, this zone is a master.  When set,
this zone is a slave.  This is a list of remotes identifiers.

@item @code{ddns-master} (default: @code{#f})
The main master.  When empty, it defaults to the first master in the list of
masters.

@item @code{notify} (default: @code{'()})
A list of slave remote identifiers.

@item @code{acl} (default: @code{'()})
A list of acl identifiers.

@item @code{semantic-checks?} (default: @code{#f})
When set, this adds more semantic checks to the zone.

@item @code{disable-any?} (default: @code{#f})
When set, this forbids queries of the ANY type.

@item @code{zonefile-sync} (default: @code{0})
The delay between a modification in memory and on disk.  0 means immediate
synchronization.

@item @code{serial-policy} (default: @code{'increment})
A policy between @code{'increment} and @code{'unixtime}.

@end table
@end deftp

@deftp {Data Type} knot-configuration
Data type representing the Knot configuration.  This type has the following
parameters:

@table @asis
@item @code{knot} (default: @code{knot})
The Knot package.

@item @code{run-directory} (default: @code{"/var/run/knot"})
The run directory.  This directory will be used for pid file and sockets.

@item @code{listen-v4} (default: @code{"0.0.0.0"})
An ip address on which to listen.

@item @code{listen-v6} (default: @code{"::"})
An ip address on which to listen.

@item @code{listen-port} (default: @code{53})
A port on which to listen.

@item @code{keys} (default: @code{'()})
The list of knot-key-configuration used by this configuration.

@item @code{acls} (default: @code{'()})
The list of knot-acl-configuration used by this configuration.

@item @code{remotes} (default: @code{'()})
The list of knot-remote-configuration used by this configuration.

@item @code{zones} (default: @code{'()})
The list of knot-zone-configuration used by this configuration.

@end table
@end deftp

@subsubheading Dnsmasq Service

@deffn {Scheme Variable} dnsmasq-service-type
This is the type of the dnsmasq service, whose value should be an
@code{dnsmasq-configuration} object as in this example:

@example
(service dnsmasq-service-type
         (dnsmasq-configuration
           (no-resolv? #t)
           (servers '("192.168.1.1"))))
@end example
@end deffn

@deftp {Data Type} dnsmasq-configuration
Data type representing the configuration of dnsmasq.

@table @asis
@item @code{package} (default: @var{dnsmasq})
Package object of the dnsmasq server.

@item @code{no-hosts?} (default: @code{#f})
When true, don't read the hostnames in /etc/hosts.

@item @code{port} (default: @code{53})
The port to listen on.  Setting this to zero completely disables DNS
responses, leaving only DHCP and/or TFTP functions.

@item @code{local-service?} (default: @code{#t})
Accept DNS queries only from hosts whose address is on a local subnet, ie a
subnet for which an interface exists on the server.

@item @code{listen-addresses} (default: @code{'()})
Listen on the given IP addresses.

@item @code{resolv-file} (default: @code{"/etc/resolv.conf"})
The file to read the IP address of the upstream nameservers from.

@item @code{no-resolv?} (default: @code{#f})
When true, don't read @var{resolv-file}.

@item @code{servers} (default: @code{'()})
Specify IP address of upstream servers directly.

@item @code{cache-size} (default: @code{150})
Set the size of dnsmasq's cache.  Setting the cache size to zero disables
caching.

@item @code{negative-cache?} (default: @code{#t})
When false, disable negative caching.

@end table
@end deftp

@subsubheading ddclient Service

@cindex ddclient
The ddclient service described below runs the ddclient daemon, which takes
care of automatically updating DNS entries for service providers such as
@uref{https://dyn.com/dns/, Dyn}.

The following example show instantiates the service with its default
configuration:

@example
(service ddclient-service-type)
@end example

Note that ddclient needs to access credentials that are stored in a
@dfn{secret file}, by default @file{/etc/ddclient/secrets} (see
@code{secret-file} below.)  You are expected to create this file manually,
in an ``out-of-band'' fashion (you @emph{could} make this file part of the
service configuration, for instance by using @code{plain-file}, but it will
be world-readable @i{via} @file{/gnu/store}.)  See the examples in the
@file{share/ddclient} directory of the @code{ddclient} package.

@c %start of fragment

Available @code{ddclient-configuration} fields are:

@deftypevr {@code{ddclient-configuration} parameter} package ddclient
The ddclient package.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} integer daemon
The period after which ddclient will retry to check IP and domain name.

Defaults to @samp{300}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} boolean syslog
Use syslog for the output.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string mail
Mail to user.

Defaults to @samp{"root"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string mail-failure
Mail failed update to user.

Defaults to @samp{"root"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string pid
The ddclient PID file.

Defaults to @samp{"/var/run/ddclient/ddclient.pid"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} boolean ssl
Enable SSL support.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string user
Specifies the user name or ID that is used when running ddclient program.

Defaults to @samp{"ddclient"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string group
Group of the user who will run the ddclient program.

Defaults to @samp{"ddclient"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string secret-file
Secret file which will be appended to @file{ddclient.conf} file.  This file
contains credentials for use by ddclient.  You are expected to create it
manually.

Defaults to @samp{"/etc/ddclient/secrets.conf"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} list extra-options
Extra options will be appended to @file{ddclient.conf} file.

Defaults to @samp{()}.

@end deftypevr


@c %end of fragment


@node VPN-Dienste
@subsubsection VPN-Dienste
@cindex VPN (virtual private network)
@cindex virtual private network (VPN)

The @code{(gnu services vpn)} module provides services related to
@dfn{virtual private networks} (VPNs).  It provides a @emph{client} service
for your machine to connect to a VPN, and a @emph{servire} service for your
machine to host a VPN.  Both services use @uref{https://openvpn.net/,
OpenVPN}.

@deffn {Scheme Procedure} openvpn-client-service @
       [#:config (openvpn-client-configuration)]

Return a service that runs @command{openvpn}, a VPN daemon, as a client.
@end deffn

@deffn {Scheme Procedure} openvpn-server-service @
       [#:config (openvpn-server-configuration)]

Return a service that runs @command{openvpn}, a VPN daemon, as a server.

Both can be run simultaneously.
@end deffn

@c %automatically generated documentation

Available @code{openvpn-client-configuration} fields are:

@deftypevr {@code{openvpn-client-configuration} parameter} package openvpn
The OpenVPN package.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} string pid-file
The OpenVPN pid file.

Defaults to @samp{"/var/run/openvpn/openvpn.pid"}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} proto proto
The protocol (UDP or TCP) used to open a channel between clients and
servers.

Defaults to @samp{udp}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} dev dev
The device type used to represent the VPN connection.

Defaults to @samp{tun}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} string ca
The certificate authority to check connections against.

Defaults to @samp{"/etc/openvpn/ca.crt"}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} string cert
The certificate of the machine the daemon is running on.  It should be
signed by the authority given in @code{ca}.

Defaults to @samp{"/etc/openvpn/client.crt"}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} string key
The key of the machine the daemon is running on.  It must be the key whose
certificate is @code{cert}.

Defaults to @samp{"/etc/openvpn/client.key"}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} boolean comp-lzo?
Whether to use the lzo compression algorithm.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} boolean persist-key?
Don't re-read key files across SIGUSR1 or --ping-restart.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} boolean persist-tun?
Don't close and reopen TUN/TAP device or run up/down scripts across SIGUSR1
or --ping-restart restarts.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} number verbosity
Verbosity level.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} tls-auth-client tls-auth
Add an additional layer of HMAC authentication on top of the TLS control
channel to protect against DoS attacks.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} key-usage verify-key-usage?
Whether to check the server certificate has server usage extension.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} bind bind?
Bind to a specific local port number.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} resolv-retry resolv-retry?
Retry resolving server address.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} openvpn-remote-list remote
A list of remote servers to connect to.

Defaults to @samp{()}.

Available @code{openvpn-remote-configuration} fields are:

@deftypevr {@code{openvpn-remote-configuration} parameter} string name
Server name.

Defaults to @samp{"my-server"}.

@end deftypevr

@deftypevr {@code{openvpn-remote-configuration} parameter} number port
Port number the server listens to.

Defaults to @samp{1194}.

@end deftypevr

@end deftypevr
@c %end of automatic openvpn-client documentation

@c %automatically generated documentation

Available @code{openvpn-server-configuration} fields are:

@deftypevr {@code{openvpn-server-configuration} parameter} package openvpn
The OpenVPN package.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string pid-file
The OpenVPN pid file.

Defaults to @samp{"/var/run/openvpn/openvpn.pid"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} proto proto
The protocol (UDP or TCP) used to open a channel between clients and
servers.

Defaults to @samp{udp}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} dev dev
The device type used to represent the VPN connection.

Defaults to @samp{tun}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string ca
The certificate authority to check connections against.

Defaults to @samp{"/etc/openvpn/ca.crt"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string cert
The certificate of the machine the daemon is running on.  It should be
signed by the authority given in @code{ca}.

Defaults to @samp{"/etc/openvpn/client.crt"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string key
The key of the machine the daemon is running on.  It must be the key whose
certificate is @code{cert}.

Defaults to @samp{"/etc/openvpn/client.key"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} boolean comp-lzo?
Whether to use the lzo compression algorithm.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} boolean persist-key?
Don't re-read key files across SIGUSR1 or --ping-restart.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} boolean persist-tun?
Don't close and reopen TUN/TAP device or run up/down scripts across SIGUSR1
or --ping-restart restarts.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} number verbosity
Verbosity level.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} tls-auth-server tls-auth
Add an additional layer of HMAC authentication on top of the TLS control
channel to protect against DoS attacks.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} number port
Specifies the port number on which the server listens.

Defaults to @samp{1194}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} ip-mask server
An ip and mask specifying the subnet inside the virtual network.

Defaults to @samp{"10.8.0.0 255.255.255.0"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} cidr6 server-ipv6
A CIDR notation specifying the IPv6 subnet inside the virtual network.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string dh
The Diffie-Hellman parameters file.

Defaults to @samp{"/etc/openvpn/dh2048.pem"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string ifconfig-pool-persist
The file that records client IPs.

Defaults to @samp{"/etc/openvpn/ipp.txt"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} gateway redirect-gateway?
When true, the server will act as a gateway for its clients.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} boolean client-to-client?
When true, clients are allowed to talk to each other inside the VPN.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} keepalive keepalive
Causes ping-like messages to be sent back and forth over the link so that
each side knows when the other side has gone down.  @code{keepalive}
requires a pair.  The first element is the period of the ping sending, and
the second element is the timeout before considering the other side down.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} number max-clients
The maximum number of clients.

Defaults to @samp{100}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string status
The status file.  This file shows a small report on current connection.  It
is truncated and rewritten every minute.

Defaults to @samp{"/var/run/openvpn/status"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} openvpn-ccd-list client-config-dir
The list of configuration for some clients.

Defaults to @samp{()}.

Available @code{openvpn-ccd-configuration} fields are:

@deftypevr {@code{openvpn-ccd-configuration} parameter} string name
Client name.

Defaults to @samp{"client"}.

@end deftypevr

@deftypevr {@code{openvpn-ccd-configuration} parameter} ip-mask iroute
Client own network

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-ccd-configuration} parameter} ip-mask ifconfig-push
Client VPN IP.

Defaults to @samp{#f}.

@end deftypevr

@end deftypevr


@c %end of automatic openvpn-server documentation


@node Network File System
@subsubsection Network File System
@cindex NFS

The @code{(gnu services nfs)} module provides the following services, which
are most commonly used in relation to mounting or exporting directory trees
as @dfn{network file systems} (NFS).

@subsubheading RPC Bind Service
@cindex rpcbind

The RPC Bind service provides a facility to map program numbers into
universal addresses.  Many NFS related services use this facility.  Hence it
is automatically started when a dependent service starts.

@defvr {Scheme Variable} rpcbind-service-type
A service type for the RPC portmapper daemon.
@end defvr


@deftp {Data Type} rpcbind-configuration
Data type representing the configuration of the RPC Bind Service.  This type
has the following parameters:
@table @asis
@item @code{rpcbind} (default: @code{rpcbind})
The rpcbind package to use.

@item @code{warm-start?} (default: @code{#t})
If this parameter is @code{#t}, then the daemon will read a state file on
startup thus reloading state information saved by a previous instance.
@end table
@end deftp


@subsubheading Pipefs Pseudo File System
@cindex pipefs
@cindex rpc_pipefs

The pipefs file system is used to transfer NFS related data between the
kernel and user space programs.

@defvr {Scheme Variable} pipefs-service-type
A service type for the pipefs pseudo file system.
@end defvr

@deftp {Data Type} pipefs-configuration
Data type representing the configuration of the pipefs pseudo file system
service.  This type has the following parameters:
@table @asis
@item @code{mount-point} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory to which the file system is to be attached.
@end table
@end deftp


@subsubheading GSS Daemon Service
@cindex GSSD
@cindex GSS
@cindex global security system

The @dfn{global security system} (GSS) daemon provides strong security for
RPC based protocols.  Before exchanging RPC requests an RPC client must
establish a security context.  Typically this is done using the Kerberos
command @command{kinit} or automatically at login time using PAM services
(@pxref{Kerberos-Dienste}).

@defvr {Scheme Variable} gss-service-type
A service type for the Global Security System (GSS) daemon.
@end defvr

@deftp {Data Type} gss-configuration
Data type representing the configuration of the GSS daemon service.  This
type has the following parameters:
@table @asis
@item @code{nfs-utils} (default: @code{nfs-utils})
The package in which the @command{rpc.gssd} command is to be found.

@item @code{pipefs-directory} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory where the pipefs file system is mounted.

@end table
@end deftp


@subsubheading IDMAP Daemon Service
@cindex idmapd
@cindex name mapper

The idmap daemon service provides mapping between user IDs and user names.
Typically it is required in order to access file systems mounted via NFSv4.

@defvr {Scheme Variable} idmap-service-type
A service type for the Identity Mapper (IDMAP) daemon.
@end defvr

@deftp {Data Type} idmap-configuration
Data type representing the configuration of the IDMAP daemon service.  This
type has the following parameters:
@table @asis
@item @code{nfs-utils} (default: @code{nfs-utils})
The package in which the @command{rpc.idmapd} command is to be found.

@item @code{pipefs-directory} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory where the pipefs file system is mounted.

@item @code{domain} (default: @code{#f})
The local NFSv4 domain name.  This must be a string or @code{#f}.  If it is
@code{#f} then the daemon will use the host's fully qualified domain name.

@end table
@end deftp

@node Kontinuierliche Integration
@subsubsection Kontinuierliche Integration

@cindex continuous integration
@uref{https://git.savannah.gnu.org/cgit/guix/guix-cuirass.git, Cuirass} is a
continuous integration tool for Guix.  It can be used both for development
and for providing substitutes to others (@pxref{Substitute}).

The @code{(gnu services cuirass)} module provides the following service.

@defvr {Scheme Procedure} cuirass-service-type
The type of the Cuirass service.  Its value must be a
@code{cuirass-configuration} object, as described below.
@end defvr

To add build jobs, you have to set the @code{specifications} field of the
configuration.  Here is an example of a service that polls the Guix
repository and builds the packages from a manifest.  Some of the packages
are defined in the @code{"custom-packages"} input, which is the equivalent
of @code{GUIX_PACKAGE_PATH}.

@example
(define %cuirass-specs
  #~(list
     '((#:name . "my-manifest")
       (#:load-path-inputs . ("guix"))
       (#:package-path-inputs . ("custom-packages"))
       (#:proc-input . "guix")
       (#:proc-file . "build-aux/cuirass/gnu-system.scm")
       (#:proc . cuirass-jobs)
       (#:proc-args . ((subset . "manifests")
                       (systems . ("x86_64-linux"))
                       (manifests . (("config" . "guix/manifest.scm")))))
       (#:inputs . (((#:name . "guix")
                     (#:url . "git://git.savannah.gnu.org/guix.git")
                     (#:load-path . ".")
                     (#:branch . "master")
                     (#:no-compile? . #t))
                    ((#:name . "config")
                     (#:url . "git://git.example.org/config.git")
                     (#:load-path . ".")
                     (#:branch . "master")
                     (#:no-compile? . #t))
                    ((#:name . "custom-packages")
                     (#:url . "git://git.example.org/custom-packages.git")
                     (#:load-path . ".")
                     (#:branch . "master")
                     (#:no-compile? . #t)))))))

(service cuirass-service-type
         (cuirass-configuration
          (specifications %cuirass-specs)))
@end example

While information related to build jobs is located directly in the
specifications, global settings for the @command{cuirass} process are
accessible in other @code{cuirass-configuration} fields.

@deftp {Data Type} cuirass-configuration
Data type representing the configuration of Cuirass.

@table @asis
@item @code{log-file} (default: @code{"/var/log/cuirass.log"})
Location of the log file.

@item @code{cache-directory} (default: @code{"/var/cache/cuirass"})
Location of the repository cache.

@item @code{user} (default: @code{"cuirass"})
Owner of the @code{cuirass} process.

@item @code{group} (default: @code{"cuirass"})
Owner's group of the @code{cuirass} process.

@item @code{interval} (default: @code{60})
Number of seconds between the poll of the repositories followed by the
Cuirass jobs.

@item @code{database} (default: @code{"/var/lib/cuirass/cuirass.db"})
Location of sqlite database which contains the build results and previously
added specifications.

@item @code{port} (default: @code{8081})
Port number used by the HTTP server.

@item --listen=@var{host}
Listen on the network interface for @var{host}.  The default is to accept
connections from localhost.

@item @code{specifications} (default: @code{#~'()})
A gexp (@pxref{G-Ausdrücke}) that evaluates to a list of specifications,
where a specification is an association list (@pxref{Associations Lists,,,
guile, GNU Guile Reference Manual}) whose keys are keywords
(@code{#:keyword-example}) as shown in the example above.

@item @code{use-substitutes?} (default: @code{#f})
This allows using substitutes to avoid building every dependencies of a job
from source.

@item @code{one-shot?} (default: @code{#f})
Only evaluate specifications and build derivations once.

@item @code{fallback?} (default: @code{#f})
When substituting a pre-built binary fails, fall back to building packages
locally.

@item @code{cuirass} (default: @code{cuirass})
The Cuirass package to use.
@end table
@end deftp

@node Power Management Services
@subsubsection Power Management Services

@cindex tlp
@cindex power management with TLP
@subsubheading TLP daemon

The @code{(gnu services pm)} module provides a Guix service definition for
the Linux power management tool TLP.

TLP enables various powersaving modes in userspace and kernel.  Contrary to
@code{upower-service}, it is not a passive, monitoring tool, as it will
apply custom settings each time a new power source is detected.  More
information can be found at @uref{http://linrunner.de/en/tlp/tlp.html, TLP
home page}.

@deffn {Scheme Variable} tlp-service-type
The service type for the TLP tool.  Its value should be a valid TLP
configuration (see below).  To use the default settings, simply write:
@example
(service tlp-service-type)
@end example
@end deffn

By default TLP does not need much configuration but most TLP parameters can
be tweaked using @code{tlp-configuration}.

Each parameter definition is preceded by its type; for example,
@samp{boolean foo} indicates that the @code{foo} parameter should be
specified as a boolean.  Types starting with @code{maybe-} denote parameters
that won't show up in TLP config file when their value is @code{'disabled}.

@c The following documentation was initially generated by
@c (generate-tlp-documentation) in (gnu services pm).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as TLP updates.

Available @code{tlp-configuration} fields are:

@deftypevr {@code{tlp-configuration} parameter} package tlp
The TLP package.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean tlp-enable?
Set to true if you wish to enable TLP.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string tlp-default-mode
Default mode when no power supply can be detected.  Alternatives are AC and
BAT.

Defaults to @samp{"AC"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer disk-idle-secs-on-ac
Number of seconds Linux kernel has to wait after the disk goes idle, before
syncing on AC.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer disk-idle-secs-on-bat
Same as @code{disk-idle-ac} but on BAT mode.

Defaults to @samp{2}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer max-lost-work-secs-on-ac
Dirty pages flushing periodicity, expressed in seconds.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer max-lost-work-secs-on-bat
Same as @code{max-lost-work-secs-on-ac} but on BAT mode.

Defaults to @samp{60}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list cpu-scaling-governor-on-ac
CPU frequency scaling governor on AC mode.  With intel_pstate driver,
alternatives are powersave and performance.  With acpi-cpufreq driver,
alternatives are ondemand, powersave, performance and conservative.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list cpu-scaling-governor-on-bat
Same as @code{cpu-scaling-governor-on-ac} but on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-min-freq-on-ac
Set the min available frequency for the scaling governor on AC.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-max-freq-on-ac
Set the max available frequency for the scaling governor on AC.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-min-freq-on-bat
Set the min available frequency for the scaling governor on BAT.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-max-freq-on-bat
Set the max available frequency for the scaling governor on BAT.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-min-perf-on-ac
Limit the min P-state to control the power dissipation of the CPU, in AC
mode.  Values are stated as a percentage of the available performance.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-max-perf-on-ac
Limit the max P-state to control the power dissipation of the CPU, in AC
mode.  Values are stated as a percentage of the available performance.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-min-perf-on-bat
Same as @code{cpu-min-perf-on-ac} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-max-perf-on-bat
Same as @code{cpu-max-perf-on-ac} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-boolean cpu-boost-on-ac?
Enable CPU turbo boost feature on AC mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-boolean cpu-boost-on-bat?
Same as @code{cpu-boost-on-ac?} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean sched-powersave-on-ac?
Allow Linux kernel to minimize the number of CPU cores/hyper-threads used
under light load conditions.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean sched-powersave-on-bat?
Same as @code{sched-powersave-on-ac?} but on BAT mode.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean nmi-watchdog?
Enable Linux kernel NMI watchdog.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string phc-controls
For Linux kernels with PHC patch applied, change CPU voltages.  An example
value would be @samp{"F:V F:V F:V F:V"}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string energy-perf-policy-on-ac
Set CPU performance versus energy saving policy on AC.  Alternatives are
performance, normal, powersave.

Defaults to @samp{"performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string energy-perf-policy-on-bat
Same as @code{energy-perf-policy-ac} but on BAT mode.

Defaults to @samp{"powersave"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list disks-devices
Hard disk devices.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list disk-apm-level-on-ac
Hard disk advanced power management level.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list disk-apm-level-on-bat
Same as @code{disk-apm-bat} but on BAT mode.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list disk-spindown-timeout-on-ac
Hard disk spin down timeout.  One value has to be specified for each
declared hard disk.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list disk-spindown-timeout-on-bat
Same as @code{disk-spindown-timeout-on-ac} but on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list disk-iosched
Select IO scheduler for disk devices.  One value has to be specified for
each declared hard disk.  Example alternatives are cfq, deadline and noop.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string sata-linkpwr-on-ac
SATA aggressive link power management (ALPM) level.  Alternatives are
min_power, medium_power, max_performance.

Defaults to @samp{"max_performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string sata-linkpwr-on-bat
Same as @code{sata-linkpwr-ac} but on BAT mode.

Defaults to @samp{"min_power"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string sata-linkpwr-blacklist
Exclude specified SATA host devices for link power management.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-on-off-boolean ahci-runtime-pm-on-ac?
Enable Runtime Power Management for AHCI controller and disks on AC mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-on-off-boolean ahci-runtime-pm-on-bat?
Same as @code{ahci-runtime-pm-on-ac} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer ahci-runtime-pm-timeout
Seconds of inactivity before disk is suspended.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string pcie-aspm-on-ac
PCI Express Active State Power Management level.  Alternatives are default,
performance, powersave.

Defaults to @samp{"performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string pcie-aspm-on-bat
Same as @code{pcie-aspm-ac} but on BAT mode.

Defaults to @samp{"powersave"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-power-profile-on-ac
Radeon graphics clock speed level.  Alternatives are low, mid, high, auto,
default.

Defaults to @samp{"high"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-power-profile-on-bat
Same as @code{radeon-power-ac} but on BAT mode.

Defaults to @samp{"low"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-state-on-ac
Radeon dynamic power management method (DPM).  Alternatives are battery,
performance.

Defaults to @samp{"performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-state-on-bat
Same as @code{radeon-dpm-state-ac} but on BAT mode.

Defaults to @samp{"battery"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-perf-level-on-ac
Radeon DPM performance level.  Alternatives are auto, low, high.

Defaults to @samp{"auto"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-perf-level-on-bat
Same as @code{radeon-dpm-perf-ac} but on BAT mode.

Defaults to @samp{"auto"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} on-off-boolean wifi-pwr-on-ac?
Wifi power saving mode.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} on-off-boolean wifi-pwr-on-bat?
Same as @code{wifi-power-ac?} but on BAT mode.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} y-n-boolean wol-disable?
Disable wake on LAN.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer sound-power-save-on-ac
Timeout duration in seconds before activating audio power saving on Intel
HDA and AC97 devices.  A value of 0 disables power saving.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer sound-power-save-on-bat
Same as @code{sound-powersave-ac} but on BAT mode.

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} y-n-boolean sound-power-save-controller?
Disable controller in powersaving mode on Intel HDA devices.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean bay-poweroff-on-bat?
Enable optical drive in UltraBay/MediaBay on BAT mode.  Drive can be powered
on again by releasing (and reinserting) the eject lever or by pressing the
disc eject button on newer models.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string bay-device
Name of the optical drive device to power off.

Defaults to @samp{"sr0"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string runtime-pm-on-ac
Runtime Power Management for PCI(e) bus devices.  Alternatives are on and
auto.

Defaults to @samp{"on"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string runtime-pm-on-bat
Same as @code{runtime-pm-ac} but on BAT mode.

Defaults to @samp{"auto"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean runtime-pm-all?
Runtime Power Management for all PCI(e) bus devices, except blacklisted
ones.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list runtime-pm-blacklist
Exclude specified PCI(e) device addresses from Runtime Power Management.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list runtime-pm-driver-blacklist
Exclude PCI(e) devices assigned to the specified drivers from Runtime Power
Management.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean usb-autosuspend?
Enable USB autosuspend feature.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string usb-blacklist
Exclude specified devices from USB autosuspend.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean usb-blacklist-wwan?
Exclude WWAN devices from USB autosuspend.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string usb-whitelist
Include specified devices into USB autosuspend, even if they are already
excluded by the driver or via @code{usb-blacklist-wwan?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-boolean usb-autosuspend-disable-on-shutdown?
Enable USB autosuspend before shutdown.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean restore-device-state-on-startup?
Restore radio device state (bluetooth, wifi, wwan) from previous shutdown on
system startup.

Defaults to @samp{#f}.

@end deftypevr

@cindex thermald
@cindex CPU frequency scaling with thermald
@subsubheading Thermald daemon

The @code{(gnu services pm)} module provides an interface to thermald, a CPU
frequency scaling service which helps prevent overheating.

@defvr {Scheme Variable} thermald-service-type
This is the service type for @uref{https://01.org/linux-thermal-daemon/,
thermald}, the Linux Thermal Daemon, which is responsible for controlling
the thermal state of processors and preventing overheating.
@end defvr

@deftp {Data Type} thermald-configuration
Data type representing the configuration of @code{thermald-service-type}.

@table @asis
@item @code{ignore-cpuid-check?} (default: @code{#f})
Ignore cpuid check for supported CPU models.

@item @code{thermald} (default: @var{thermald})
Package object of thermald.

@end table
@end deftp

@node Audio-Dienste
@subsubsection Audio-Dienste

The @code{(gnu services audio)} module provides a service to start MPD (the
Music Player Daemon).

@cindex mpd
@subsubheading Music Player Daemon

The Music Player Daemon (MPD) is a service that can play music while being
controlled from the local machine or over the network by a variety of
clients.

The following example shows how one might run @code{mpd} as user
@code{"bob"} on port @code{6666}.  It uses pulseaudio for output.

@example
(service mpd-service-type
         (mpd-configuration
          (user "bob")
          (port "6666")))
@end example

@defvr {Scheme Variable} mpd-service-type
The service type for @command{mpd}
@end defvr

@deftp {Data Type} mpd-configuration
Data type representing the configuration of @command{mpd}.

@table @asis
@item @code{user} (default: @code{"mpd"})
The user to run mpd as.

@item @code{music-dir} (default: @code{"~/Music"})
The directory to scan for music files.

@item @code{playlist-dir} (default: @code{"~/.mpd/playlists"})
The directory to store playlists.

@item @code{port} (default: @code{"6600"})
The port to run mpd on.

@item @code{address} (default: @code{"any"})
The address that mpd will bind to.  To use a Unix domain socket, an absolute
path can be specified here.

@end table
@end deftp

@node Virtualisierungsdienste
@subsubsection Virtualization services

The @code{(gnu services virtualization)} module provides services for the
libvirt and virtlog daemons, as well as other virtualization-related
services.

@subsubheading Libvirt daemon
@code{libvirtd} is the server side daemon component of the libvirt
virtualization management system. This daemon runs on host servers and
performs required management tasks for virtualized guests.

@deffn {Scheme Variable} libvirt-service-type
This is the type of the @uref{https://libvirt.org, libvirt daemon}.  Its
value must be a @code{libvirt-configuration}.

@example
(service libvirt-service-type
         (libvirt-configuration
          (unix-sock-group "libvirt")
          (tls-port "16555")))
@end example
@end deffn

@c Auto-generated with (generate-libvirt-documentation)
Available @code{libvirt-configuration} fields are:

@deftypevr {@code{libvirt-configuration} parameter} package libvirt
Libvirt package.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean listen-tls?
Flag listening for secure TLS connections on the public TCP/IP port.  must
set @code{listen} for this to have any effect.

It is necessary to setup a CA and issue server certificates before using
this capability.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean listen-tcp?
Listen for unencrypted TCP connections on the public TCP/IP port.  must set
@code{listen} for this to have any effect.

Using the TCP socket requires SASL authentication by default.  Only SASL
mechanisms which support data encryption are allowed.  This is DIGEST_MD5
and GSSAPI (Kerberos5)

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string tls-port
Port for accepting secure TLS connections This can be a port number, or
service name

Defaults to @samp{"16514"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string tcp-port
Port for accepting insecure TCP connections This can be a port number, or
service name

Defaults to @samp{"16509"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string listen-addr
IP address or hostname used for client connections.

Defaults to @samp{"0.0.0.0"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean mdns-adv?
Flag toggling mDNS advertisement of the libvirt service.

Alternatively can disable for all services on a host by stopping the Avahi
daemon.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string mdns-name
Default mDNS advertisement name.  This must be unique on the immediate
broadcast network.

Defaults to @samp{"Virtualization Host <hostname>"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-group
UNIX domain socket group ownership.  This can be used to allow a 'trusted'
set of users access to management capabilities without becoming root.

Defaults to @samp{"root"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-ro-perms
UNIX socket permissions for the R/O socket.  This is used for monitoring VM
status only.

Defaults to @samp{"0777"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-rw-perms
UNIX socket permissions for the R/W socket.  Default allows only root.  If
PolicyKit is enabled on the socket, the default will change to allow
everyone (eg, 0777)

Defaults to @samp{"0770"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-admin-perms
UNIX socket permissions for the admin socket.  Default allows only owner
(root), do not change it unless you are sure to whom you are exposing the
access to.

Defaults to @samp{"0777"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-dir
The directory in which sockets will be found/created.

Defaults to @samp{"/var/run/libvirt"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-unix-ro
Authentication scheme for UNIX read-only sockets.  By default socket
permissions allow anyone to connect

Defaults to @samp{"polkit"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-unix-rw
Authentication scheme for UNIX read-write sockets.  By default socket
permissions only allow root.  If PolicyKit support was compiled into
libvirt, the default will be to use 'polkit' auth.

Defaults to @samp{"polkit"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-tcp
Authentication scheme for TCP sockets.  If you don't enable SASL, then all
TCP traffic is cleartext.  Don't do this outside of a dev/test scenario.

Defaults to @samp{"sasl"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-tls
Authentication scheme for TLS sockets.  TLS sockets already have encryption
provided by the TLS layer, and limited authentication is done by
certificates.

It is possible to make use of any SASL authentication mechanism as well, by
using 'sasl' for this option

Defaults to @samp{"none"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-list access-drivers
API access control scheme.

By default an authenticated user is allowed access to all APIs.  Access
drivers can place restrictions on this.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string key-file
Server key file path.  If set to an empty string, then no private key is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string cert-file
Server key file path.  If set to an empty string, then no certificate is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string ca-file
Server key file path.  If set to an empty string, then no CA certificate is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string crl-file
Certificate revocation list path.  If set to an empty string, then no CRL is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean tls-no-sanity-cert
Disable verification of our own server certificates.

When libvirtd starts it performs some sanity checks against its own
certificates.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean tls-no-verify-cert
Disable verification of client certificates.

Client certificate verification is the primary authentication mechanism.
Any client which does not present a certificate signed by the CA will be
rejected.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-list tls-allowed-dn-list
Whitelist of allowed x509 Distinguished Name.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-list sasl-allowed-usernames
Whitelist of allowed SASL usernames.  The format for username depends on the
SASL authentication mechanism.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string tls-priority
Override the compile time default TLS priority string.  The default is
usually "NORMAL" unless overridden at build time.  Only set this is it is
desired for libvirt to deviate from the global default settings.

Defaults to @samp{"NORMAL"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-clients
Maximum number of concurrent client connections to allow over all sockets
combined.

Defaults to @samp{5000}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-queued-clients
Maximum length of queue of connections waiting to be accepted by the
daemon.  Note, that some protocols supporting retransmission may obey this
so that a later reattempt at connection succeeds.

Defaults to @samp{1000}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-anonymous-clients
Maximum length of queue of accepted but not yet authenticated clients.  Set
this to zero to turn this feature off

Defaults to @samp{20}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer min-workers
Number of workers to start up initially.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-workers
Maximum number of worker threads.

If the number of active clients exceeds @code{min-workers}, then more
threads are spawned, up to max_workers limit.  Typically you'd want
max_workers to equal maximum number of clients allowed.

Defaults to @samp{20}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer prio-workers
Number of priority workers.  If all workers from above pool are stuck, some
calls marked as high priority (notably domainDestroy) can be executed in
this pool.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-requests
Total global limit on concurrent RPC calls.

Defaults to @samp{20}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-client-requests
Limit on concurrent requests from a single client connection.  To avoid one
client monopolizing the server this should be a small fraction of the global
max_requests and max_workers parameter.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-min-workers
Same as @code{min-workers} but for the admin interface.

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-workers
Same as @code{max-workers} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-clients
Same as @code{max-clients} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-queued-clients
Same as @code{max-queued-clients} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-client-requests
Same as @code{max-client-requests} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer log-level
Logging level.  4 errors, 3 warnings, 2 information, 1 debug.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string log-filters
Logging filters.

A filter allows to select a different logging level for a given category of
logs The format for a filter is one of:

@itemize @bullet
@item
x:name

@item
x:+name

@end itemize

where @code{name} is a string which is matched against the category given in
the @code{VIR_LOG_INIT()} at the top of each libvirt source file, e.g.,
"remote", "qemu", or "util.json" (the name in the filter can be a substring
of the full category name, in order to match multiple similar categories),
the optional "+" prefix tells libvirt to log stack trace for each message
matching name, and @code{x} is the minimal level where matching messages
should be logged:

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple filters can be defined in a single filters statement, they just
need to be separated by spaces.

Defaults to @samp{"3:remote 4:event"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string log-outputs
Logging outputs.

An output is one of the places to save logging information The format for an
output can be:

@table @code
@item x:stderr
output goes to stderr

@item x:syslog:name
use syslog for the output and use the given name as the ident

@item x:file:file_path
output to a file, with the given filepath

@item x:journald
output to journald logging system

@end table

In all case the x prefix is the minimal level, acting as a filter

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple outputs can be defined, they just need to be separated by spaces.

Defaults to @samp{"3:stderr"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer audit-level
Allows usage of the auditing subsystem to be altered

@itemize @bullet
@item
0: disable all auditing

@item
1: enable auditing, only if enabled on host

@item
2: enable auditing, and exit if disabled on host.

@end itemize

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean audit-logging
Send audit messages via libvirt logging infrastructure.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-string host-uuid
Host UUID.  UUID must not have all digits be the same.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string host-uuid-source
Source to read host UUID.

@itemize @bullet
@item
@code{smbios}: fetch the UUID from @code{dmidecode -s system-uuid}

@item
@code{machine-id}: fetch the UUID from @code{/etc/machine-id}

@end itemize

If @code{dmidecode} does not provide a valid UUID a temporary UUID will be
generated.

Defaults to @samp{"smbios"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer keepalive-interval
A keepalive message is sent to a client after @code{keepalive_interval}
seconds of inactivity to check if the client is still responding.  If set to
-1, libvirtd will never send keepalive requests; however clients can still
send them and the daemon will send responses.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer keepalive-count
Maximum number of keepalive messages that are allowed to be sent to the
client without getting any response before the connection is considered
broken.

In other words, the connection is automatically closed approximately after
@code{keepalive_interval * (keepalive_count + 1)} seconds since the last
message received from the client.  When @code{keepalive-count} is set to 0,
connections will be automatically closed after @code{keepalive-interval}
seconds of inactivity without sending any keepalive messages.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-keepalive-interval
Same as above but for admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-keepalive-count
Same as above but for admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer ovs-timeout
Timeout for Open vSwitch calls.

The @code{ovs-vsctl} utility is used for the configuration and its timeout
option is set by default to 5 seconds to avoid potential infinite waits
blocking libvirt.

Defaults to @samp{5}.

@end deftypevr

@c %end of autogenerated docs

@subsubheading Virtlog daemon
The virtlogd service is a server side daemon component of libvirt that is
used to manage logs from virtual machine consoles.

This daemon is not used directly by libvirt client applications, rather it
is called on their behalf by @code{libvirtd}. By maintaining the logs in a
standalone daemon, the main @code{libvirtd} daemon can be restarted without
risk of losing logs. The @code{virtlogd} daemon has the ability to re-exec()
itself upon receiving @code{SIGUSR1}, to allow live upgrades without
downtime.

@deffn {Scheme Variable} virtlog-service-type
This is the type of the virtlog daemon.  Its value must be a
@code{virtlog-configuration}.

@example
(service virtlog-service-type
         (virtlog-configuration
          (max-clients 1000)))
@end example
@end deffn

@deftypevr {@code{virtlog-configuration} parameter} integer log-level
Logging level.  4 errors, 3 warnings, 2 information, 1 debug.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} string log-filters
Logging filters.

A filter allows to select a different logging level for a given category of
logs The format for a filter is one of:

@itemize @bullet
@item
x:name

@item
x:+name

@end itemize

where @code{name} is a string which is matched against the category given in
the @code{VIR_LOG_INIT()} at the top of each libvirt source file, e.g.,
"remote", "qemu", or "util.json" (the name in the filter can be a substring
of the full category name, in order to match multiple similar categories),
the optional "+" prefix tells libvirt to log stack trace for each message
matching name, and @code{x} is the minimal level where matching messages
should be logged:

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple filters can be defined in a single filters statement, they just
need to be separated by spaces.

Defaults to @samp{"3:remote 4:event"}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} string log-outputs
Logging outputs.

An output is one of the places to save logging information The format for an
output can be:

@table @code
@item x:stderr
output goes to stderr

@item x:syslog:name
use syslog for the output and use the given name as the ident

@item x:file:file_path
output to a file, with the given filepath

@item x:journald
output to journald logging system

@end table

In all case the x prefix is the minimal level, acting as a filter

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple outputs can be defined, they just need to be separated by spaces.

Defaults to @samp{"3:stderr"}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer max-clients
Maximum number of concurrent client connections to allow over all sockets
combined.

Defaults to @samp{1024}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer max-size
Maximum file size before rolling over.

Defaults to @samp{2MB}

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer max-backups
Maximum number of backup files to keep.

Defaults to @samp{3}

@end deftypevr

@subsubheading Transparent Emulation with QEMU

@cindex emulation
@cindex @code{binfmt_misc}
@code{qemu-binfmt-service-type} provides support for transparent emulation
of program binaries built for different architectures---e.g., it allows you
to transparently execute an ARMv7 program on an x86_64 machine.  It achieves
this by combining the @uref{https://www.qemu.org, QEMU} emulator and the
@code{binfmt_misc} feature of the kernel Linux.

@defvr {Scheme Variable} qemu-binfmt-service-type
This is the type of the QEMU/binfmt service for transparent emulation.  Its
value must be a @code{qemu-binfmt-configuration} object, which specifies the
QEMU package to use as well as the architecture we want to emulated:

@example
(service qemu-binfmt-service-type
         (qemu-binfmt-configuration
           (platforms (lookup-qemu-platforms "arm" "aarch64" "ppc"))))
@end example

In this example, we enable transparent emulation for the ARM and aarch64
platforms.  Running @code{herd stop qemu-binfmt} turns it off, and running
@code{herd start qemu-binfmt} turns it back on (@pxref{Invoking herd, the
@command{herd} command,, shepherd, The GNU Shepherd Manual}).
@end defvr

@deftp {Data Type} qemu-binfmt-configuration
This is the configuration for the @code{qemu-binfmt} service.

@table @asis
@item @code{platforms} (default: @code{'()})
The list of emulated QEMU platforms.  Each item must be a @dfn{platform
object} as returned by @code{lookup-qemu-platforms} (see below).

@item @code{guix-support?} (default: @code{#f})
When it is true, QEMU and all its dependencies are added to the build
environment of @command{guix-daemon} (@pxref{Aufruf des guix-daemon,
@code{--chroot-directory} option}).  This allows the @code{binfmt_misc}
handlers to be used within the build environment, which in turn means that
you can transparently build programs for another architecture.

For example, let's suppose you're on an x86_64 machine and you have this
service:

@example
(service qemu-binfmt-service-type
         (qemu-binfmt-configuration
           (platforms (lookup-qemu-platforms "arm"))
           (guix-support? #t)))
@end example

You can run:

@example
guix build -s armhf-linux inkscape
@end example

@noindent
and it will build Inkscape for ARMv7 @emph{as if it were a native build},
transparently using QEMU to emulate the ARMv7 CPU.  Pretty handy if you'd
like to test a package build for an architecture you don't have access to!

@item @code{qemu} (default: @code{qemu})
The QEMU package to use.
@end table
@end deftp

@deffn {Scheme Procedure} lookup-qemu-platforms @var{platforms}@dots{}
Return the list of QEMU platform objects corresponding to
@var{platforms}@dots{}.  @var{platforms} must be a list of strings
corresponding to platform names, such as @code{"arm"}, @code{"sparc"},
@code{"mips64el"}, and so on.
@end deffn

@deffn {Scheme Procedure} qemu-platform? @var{obj}
Return true if @var{obj} is a platform object.
@end deffn

@deffn {Scheme Procedure} qemu-platform-name @var{platform}
Return the name of @var{platform}---a string such as @code{"arm"}.
@end deffn

@node Versionskontrolldienste
@subsubsection Versionskontrolldienste

The @code{(gnu services version-control)} module provides a service to allow
remote access to local Git repositories.  There are three options: the
@code{git-daemon-service}, which provides access to repositories via the
@code{git://} unsecured TCP-based protocol, extending the @code{nginx} web
server to proxy some requests to @code{git-http-backend}, or providing a web
interface with @code{cgit-service-type}.

@deffn {Scheme Procedure} git-daemon-service [#:config (git-daemon-configuration)]

Return a service that runs @command{git daemon}, a simple TCP server to
expose repositories over the Git protocol for anonymous access.

The optional @var{config} argument should be a
@code{<git-daemon-configuration>} object, by default it allows read-only
access to exported@footnote{By creating the magic file
"git-daemon-export-ok" in the repository directory.} repositories under
@file{/srv/git}.

@end deffn

@deftp {Data Type} git-daemon-configuration
Data type representing the configuration for @code{git-daemon-service}.

@table @asis
@item @code{package} (default: @var{git})
Package object of the Git distributed version control system.

@item @code{export-all?} (default: @var{#f})
Whether to allow access for all Git repositories, even if they do not have
the @file{git-daemon-export-ok} file.

@item @code{base-path} (default: @file{/srv/git})
Whether to remap all the path requests as relative to the given path.  If
you run git daemon with @var{(base-path "/srv/git")} on example.com, then if
you later try to pull @code{git://example.com/hello.git}, git daemon will
interpret the path as @code{/srv/git/hello.git}.

@item @code{user-path} (default: @var{#f})
Whether to allow @code{~user} notation to be used in requests.  When
specified with empty string, requests to @code{git://host/~alice/foo} is
taken as a request to access @code{foo} repository in the home directory of
user @code{alice}.  If @var{(user-path "path")} is specified, the same
request is taken as a request to access @code{path/foo} repository in the
home directory of user @code{alice}.

@item @code{listen} (default: @var{'()})
Whether to listen on specific IP addresses or hostnames, defaults to all.

@item @code{port} (default: @var{#f})
Whether to listen on an alternative port, which defaults to 9418.

@item @code{whitelist} (default: @var{'()})
If not empty, only allow access to this list of directories.

@item @code{extra-options} (default: @var{'()})
Extra options will be passed to @code{git daemon}, please run @command{man
git-daemon} for more information.

@end table
@end deftp

The @code{git://} protocol lacks authentication.  When you pull from a
repository fetched via @code{git://}, you don't know that the data you
receive was modified is really coming from the specified host, and you have
your connection is subject to eavesdropping.  It's better to use an
authenticated and encrypted transport, such as @code{https}.  Although Git
allows you to serve repositories using unsophisticated file-based web
servers, there is a faster protocol implemented by the
@code{git-http-backend} program.  This program is the back-end of a proper
Git web service.  It is designed to sit behind a FastCGI proxy.  @xref{Web-Dienste}, for more on running the necessary @code{fcgiwrap} daemon.

Guix has a separate configuration data type for serving Git repositories
over HTTP.

@deftp {Data Type} git-http-configuration
Data type representing the configuration for @code{git-http-service}.

@table @asis
@item @code{package} (default: @var{git})
Package object of the Git distributed version control system.

@item @code{git-root} (default: @file{/srv/git})
Directory containing the Git repositories to expose to the world.

@item @code{export-all?} (default: @var{#f})
Whether to expose access for all Git repositories in @var{git-root}, even if
they do not have the @file{git-daemon-export-ok} file.

@item @code{uri-path} (default: @file{/git/})
Path prefix for Git access.  With the default @code{/git/} prefix, this will
map @code{http://@var{server}/git/@var{repo}.git} to
@code{/srv/git/@var{repo}.git}.  Requests whose URI paths do not begin with
this prefix are not passed on to this Git instance.

@item @code{fcgiwrap-socket} (default: @code{127.0.0.1:9000})
The socket on which the @code{fcgiwrap} daemon is listening.  @xref{Web-Dienste}.
@end table
@end deftp

There is no @code{git-http-service-type}, currently; instead you can create
an @code{nginx-location-configuration} from a @code{git-http-configuration}
and then add that location to a web server.

@deffn {Scheme Procedure} git-http-nginx-location-configuration @
       [config=(git-http-configuration)] Compute an
@code{nginx-location-configuration} that corresponds to the given Git http
configuration.  An example nginx service definition to serve the default
@file{/srv/git} over HTTPS might be:

@example
(service nginx-service-type
         (nginx-configuration
          (server-blocks
           (list
            (nginx-server-configuration
             (listen '("443 ssl"))
             (server-name "git.my-host.org")
             (ssl-certificate
              "/etc/letsencrypt/live/git.my-host.org/fullchain.pem")
             (ssl-certificate-key
              "/etc/letsencrypt/live/git.my-host.org/privkey.pem")
             (locations
              (list
               (git-http-nginx-location-configuration
                (git-http-configuration (uri-path "/"))))))))))
@end example

This example assumes that you are using Let's Encrypt to get your TLS
certificate.  @xref{Zertifikatsdienste}.  The default @code{certbot}
service will redirect all HTTP traffic on @code{git.my-host.org} to HTTPS.
You will also need to add an @code{fcgiwrap} proxy to your system services.
@xref{Web-Dienste}.
@end deffn

@subsubheading Cgit Service

@cindex Cgit service
@cindex Git, web interface
@uref{https://git.zx2c4.com/cgit/, Cgit} is a web frontend for Git
repositories written in C.

The following example will configure the service with default values.  By
default, Cgit can be accessed on port 80 (@code{http://localhost:80}).

@example
(service cgit-service-type)
@end example

The @code{file-object} type designates either a file-like object
(@pxref{G-Ausdrücke, file-like objects}) or a string.

@c %start of fragment

Available @code{cgit-configuration} fields are:

@deftypevr {@code{cgit-configuration} parameter} package package
The CGIT package.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} nginx-server-configuration-list nginx
NGINX configuration.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object about-filter
Specifies a command which will be invoked to format the content of about
pages (both top-level and for each repository).

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string agefile
Specifies a path, relative to each repository path, which can be used to
specify the date and time of the youngest commit in the repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object auth-filter
Specifies a command that will be invoked for authenticating repository
access.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string branch-sort
Flag which, when set to @samp{age}, enables date ordering in the branch ref
list, and when set @samp{name} enables ordering by branch name.

Defaults to @samp{"name"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string cache-root
Path used to store the cgit cache entries.

Defaults to @samp{"/var/cache/cgit"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-static-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of repository pages accessed with a fixed SHA1.

Defaults to @samp{-1}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-dynamic-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of repository pages accessed without a fixed SHA1.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-repo-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of the repository summary page.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-root-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of the repository index page.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-scanrc-ttl
Number which specifies the time-to-live, in minutes, for the result of
scanning a path for Git repositories.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-about-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of the repository about page.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-snapshot-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of snapshots.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-size
The maximum number of entries in the cgit cache.  When set to @samp{0},
caching is disabled.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean case-sensitive-sort?
Sort items in the repo list case sensitively.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list clone-prefix
List of common prefixes which, when combined with a repository URL,
generates valid clone URLs for the repository.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list clone-url
List of @code{clone-url} templates.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object commit-filter
Command which will be invoked to format commit messages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string commit-sort
Flag which, when set to @samp{date}, enables strict date ordering in the
commit log, and when set to @samp{topo} enables strict topological ordering.

Defaults to @samp{"git log"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object css
URL which specifies the css document to include in all cgit pages.

Defaults to @samp{"/share/cgit/cgit.css"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object email-filter
Specifies a command which will be invoked to format names and email address
of committers, authors, and taggers, as represented in various places
throughout the cgit interface.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean embedded?
Flag which, when set to @samp{#t}, will make cgit generate a HTML fragment
suitable for embedding in other HTML pages.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-commit-graph?
Flag which, when set to @samp{#t}, will make cgit print an ASCII-art commit
history graph to the left of the commit messages in the repository log page.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-filter-overrides?
Flag which, when set to @samp{#t}, allows all filter settings to be
overridden in repository-specific cgitrc files.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-follow-links?
Flag which, when set to @samp{#t}, allows users to follow a file in the log
view.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-http-clone?
If set to @samp{#t}, cgit will act as an dumb HTTP endpoint for Git clones.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-index-links?
Flag which, when set to @samp{#t}, will make cgit generate extra links
"summary", "commit", "tree" for each repo in the repository index.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-index-owner?
Flag which, when set to @samp{#t}, will make cgit display the owner of each
repo in the repository index.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-log-filecount?
Flag which, when set to @samp{#t}, will make cgit print the number of
modified files for each commit on the repository log page.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-log-linecount?
Flag which, when set to @samp{#t}, will make cgit print the number of added
and removed lines for each commit on the repository log page.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-remote-branches?
Flag which, when set to @code{#t}, will make cgit display remote branches in
the summary and refs views.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-subject-links?
Flag which, when set to @code{1}, will make cgit use the subject of the
parent commit as link text when generating links to parent commits in commit
view.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-html-serving?
Flag which, when set to @samp{#t}, will make cgit use the subject of the
parent commit as link text when generating links to parent commits in commit
view.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-tree-linenumbers?
Flag which, when set to @samp{#t}, will make cgit generate linenumber links
for plaintext blobs printed in the tree view.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-git-config?
Flag which, when set to @samp{#f}, will allow cgit to use Git config to set
any repo specific settings.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object favicon
URL used as link to a shortcut icon for cgit.

Defaults to @samp{"/favicon.ico"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string footer
The content of the file specified with this option will be included verbatim
at the bottom of all pages (i.e.  it replaces the standard "generated by..."
message).

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string head-include
The content of the file specified with this option will be included verbatim
in the HTML HEAD section on all pages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string header
The content of the file specified with this option will be included verbatim
at the top of all pages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object include
Name of a configfile to include before the rest of the current config- file
is parsed.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string index-header
The content of the file specified with this option will be included verbatim
above the repository index.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string index-info
The content of the file specified with this option will be included verbatim
below the heading on the repository index page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean local-time?
Flag which, if set to @samp{#t}, makes cgit print commit and tag times in
the servers timezone.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object logo
URL which specifies the source of an image which will be used as a logo on
all cgit pages.

Defaults to @samp{"/share/cgit/cgit.png"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string logo-link
URL loaded when clicking on the cgit logo image.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object owner-filter
Command which will be invoked to format the Owner column of the main page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-atom-items
Number of items to display in atom feeds view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-commit-count
Number of entries to list per page in "log" view.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-message-length
Number of commit message characters to display in "log" view.

Defaults to @samp{80}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-repo-count
Specifies the number of entries to list per page on the repository index
page.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-repodesc-length
Specifies the maximum number of repo description characters to display on
the repository index page.

Defaults to @samp{80}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-blob-size
Specifies the maximum size of a blob to display HTML for in KBytes.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string max-stats
Maximum statistics period.  Valid values are @samp{week},@samp{month},
@samp{quarter} and @samp{year}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} mimetype-alist mimetype
Mimetype for the specified filename extension.

Defaults to @samp{((gif "image/gif") (html "text/html") (jpg "image/jpeg")
(jpeg "image/jpeg") (pdf "application/pdf") (png "image/png") (svg
"image/svg+xml"))}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object mimetype-file
Specifies the file to use for automatic mimetype lookup.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string module-link
Text which will be used as the formatstring for a hyperlink when a submodule
is printed in a directory listing.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean nocache?
If set to the value @samp{#t} caching will be disabled.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean noplainemail?
If set to @samp{#t} showing full author email addresses will be disabled.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean noheader?
Flag which, when set to @samp{#t}, will make cgit omit the standard header
on all pages.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} project-list project-list
A list of subdirectories inside of @code{repository-directory}, relative to
it, that should loaded as Git repositories.  An empty list means that all
subdirectories will be loaded.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object readme
Text which will be used as default value for @code{cgit-repo-readme}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean remove-suffix?
If set to @code{#t} and @code{repository-directory} is enabled, if any
repositories are found with a suffix of @code{.git}, this suffix will be
removed for the URL and name.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer renamelimit
Maximum number of files to consider when detecting renames.

Defaults to @samp{-1}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string repository-sort
The way in which repositories in each section are sorted.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} robots-list robots
Text used as content for the @code{robots} meta-tag.

Defaults to @samp{("noindex" "nofollow")}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string root-desc
Text printed below the heading on the repository index page.

Defaults to @samp{"a fast webinterface for the git dscm"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string root-readme
The content of the file specified with this option will be included verbatim
below thef "about" link on the repository index page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string root-title
Text printed as heading on the repository index page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean scan-hidden-path
If set to @samp{#t} and repository-directory is enabled,
repository-directory will recurse into directories whose name starts with a
period.  Otherwise, repository-directory will stay away from such
directories, considered as "hidden".  Note that this does not apply to the
".git" directory in non-bare repos.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list snapshots
Text which specifies the default set of snapshot formats that cgit generates
links for.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} repository-directory repository-directory
Name of the directory to scan for repositories (represents
@code{scan-path}).

Defaults to @samp{"/srv/git"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string section
The name of the current repository section - all repositories defined after
this option will inherit the current section name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string section-sort
Flag which, when set to @samp{1}, will sort the sections on the repository
listing by name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer section-from-path
A number which, if defined prior to repository-directory, specifies how many
path elements from each repo path to use as a default section name.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean side-by-side-diffs?
If set to @samp{#t} shows side-by-side diffs instead of unidiffs per
default.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object source-filter
Specifies a command which will be invoked to format plaintext blobs in the
tree view.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer summary-branches
Specifies the number of branches to display in the repository "summary"
view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer summary-log
Specifies the number of log entries to display in the repository "summary"
view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer summary-tags
Specifies the number of tags to display in the repository "summary" view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string strict-export
Filename which, if specified, needs to be present within the repository for
cgit to allow access to that repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string virtual-root
URL which, if specified, will be used as root for all cgit links.

Defaults to @samp{"/"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} repository-cgit-configuration-list repositories
A list of @dfn{cgit-repo} records to use with config.

Defaults to @samp{()}.

Available @code{repository-cgit-configuration} fields are:

@deftypevr {@code{repository-cgit-configuration} parameter} repo-list snapshots
A mask of snapshot formats for this repo that cgit generates links for,
restricted by the global @code{snapshots} setting.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object source-filter
Override the default @code{source-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string url
The relative URL used to access the repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object about-filter
Override the default @code{about-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string branch-sort
Flag which, when set to @samp{age}, enables date ordering in the branch ref
list, and when set to @samp{name} enables ordering by branch name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-list clone-url
A list of URLs which can be used to clone repo.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object commit-filter
Override the default @code{commit-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string commit-sort
Flag which, when set to @samp{date}, enables strict date ordering in the
commit log, and when set to @samp{topo} enables strict topological ordering.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string defbranch
The name of the default branch for this repository.  If no such branch
exists in the repository, the first branch name (when sorted) is used as
default instead.  By default branch pointed to by HEAD, or "master" if there
is no suitable HEAD.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string desc
The value to show as repository description.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string homepage
The value to show as repository homepage.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object email-filter
Override the default @code{email-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-commit-graph?
A flag which can be used to disable the global setting
@code{enable-commit-graph?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-log-filecount?
A flag which can be used to disable the global setting
@code{enable-log-filecount?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-log-linecount?
A flag which can be used to disable the global setting
@code{enable-log-linecount?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-remote-branches?
Flag which, when set to @code{#t}, will make cgit display remote branches in
the summary and refs views.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-subject-links?
A flag which can be used to override the global setting
@code{enable-subject-links?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-html-serving?
A flag which can be used to override the global setting
@code{enable-html-serving?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-boolean hide?
Flag which, when set to @code{#t}, hides the repository from the repository
index.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-boolean ignore?
Flag which, when set to @samp{#t}, ignores the repository.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object logo
URL which specifies the source of an image which will be used as a logo on
this repo’s pages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string logo-link
URL loaded when clicking on the cgit logo image.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object owner-filter
Override the default @code{owner-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string module-link
Text which will be used as the formatstring for a hyperlink when a submodule
is printed in a directory listing.  The arguments for the formatstring are
the path and SHA1 of the submodule commit.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} module-link-path module-link-path
Text which will be used as the formatstring for a hyperlink when a submodule
with the specified subdirectory path is printed in a directory listing.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string max-stats
Override the default maximum statistics period.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string name
The value to show as repository name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string owner
A value used to identify the owner of the repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string path
An absolute path to the repository directory.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string readme
A path (relative to repo) which specifies a file to include verbatim as the
"About" page for this repo.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string section
The name of the current repository section - all repositories defined after
this option will inherit the current section name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-list extra-options
Extra options will be appended to cgitrc file.

Defaults to @samp{()}.

@end deftypevr

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list extra-options
Extra options will be appended to cgitrc file.

Defaults to @samp{()}.

@end deftypevr


@c %end of fragment

However, it could be that you just want to get a @code{cgitrc} up and
running.  In that case, you can pass an @code{opaque-cgit-configuration} as
a record to @code{cgit-service-type}.  As its name indicates, an opaque
configuration does not have easy reflective capabilities.

Available @code{opaque-cgit-configuration} fields are:

@deftypevr {@code{opaque-cgit-configuration} parameter} package cgit
The cgit package.
@end deftypevr

@deftypevr {@code{opaque-cgit-configuration} parameter} string string
The contents of the @code{cgitrc}, as a string.
@end deftypevr

For example, if your @code{cgitrc} is just the empty string, you could
instantiate a cgit service like this:

@example
(service cgit-service-type
         (opaque-cgit-configuration
          (cgitrc "")))
@end example

@subsubheading Gitolite Service

@cindex Gitolite service
@cindex Git, hosting
@uref{http://gitolite.com/gitolite/, Gitolite} is a tool for hosting Git
repositories on a central server.

Gitolite can handle multiple repositories and users, and supports flexible
configuration of the permissions for the users on the repositories.

The following example will configure Gitolite using the default @code{git}
user, and the provided SSH public key.

@example
(service gitolite-service-type
         (gitolite-configuration
           (admin-pubkey (plain-file
                           "yourname.pub"
                           "ssh-rsa AAAA... guix@@example.com"))))
@end example

Gitolite is configured through a special admin repository which you can
clone, for example, if you setup Gitolite on @code{example.com}, you would
run the following command to clone the admin repository.

@example
git clone git@@example.com:gitolite-admin
@end example

When the Gitolite service is activated, the provided @code{admin-pubkey}
will be inserted in to the @file{keydir} directory in the gitolite-admin
repository.  If this results in a change in the repository, it will be
committed using the message ``gitolite setup by GNU Guix''.

@deftp {Data Type} gitolite-configuration
Data type representing the configuration for @code{gitolite-service-type}.

@table @asis
@item @code{package} (default: @var{gitolite})
Gitolite package to use.

@item @code{user} (default: @var{git})
User to use for Gitolite.  This will be user that you use when accessing
Gitolite over SSH.

@item @code{group} (default: @var{git})
Group to use for Gitolite.

@item @code{home-directory} (default: @var{"/var/lib/gitolite"})
Directory in which to store the Gitolite configuration and repositories.

@item @code{rc-file} (default: @var{(gitolite-rc-file)})
A ``file-like'' object (@pxref{G-Ausdrücke, file-like objects}),
representing the configuration for Gitolite.

@item @code{admin-pubkey} (default: @var{#f})
A ``file-like'' object (@pxref{G-Ausdrücke, file-like objects}) used to
setup Gitolite.  This will be inserted in to the @file{keydir} directory
within the gitolite-admin repository.

To specify the SSH key as a string, use the @code{plain-file} function.

@example
(plain-file "yourname.pub" "ssh-rsa AAAA... guix@@example.com")
@end example

@end table
@end deftp

@deftp {Data Type} gitolite-rc-file
Data type representing the Gitolite RC file.

@table @asis
@item @code{umask} (default: @code{#o0077})
This controls the permissions Gitolite sets on the repositories and their
contents.

A value like @code{#o0027} will give read access to the group used by
Gitolite (by default: @code{git}). This is necessary when using Gitolite
with software like cgit or gitweb.

@item @code{git-config-keys} (default: @code{""})
Gitolite allows you to set git config values using the "config"
keyword. This setting allows control over the config keys to accept.

@item @code{roles} (default: @code{'(("READERS" . 1) ("WRITERS" . ))})
Set the role names allowed to be used by users running the perms command.

@item @code{enable} (default: @code{'("help" "desc" "info" "perms" "writable" "ssh-authkeys" "git-config" "daemon" "gitweb")})
This setting controls the commands and features to enable within Gitolite.

@end table
@end deftp


@node Spieldienste
@subsubsection Spieldienste

@subsubheading The Battle for Wesnoth Service
@cindex wesnothd
@uref{https://wesnoth.org, The Battle for Wesnoth} is a fantasy, turn based
tactical strategy game, with several single player campaigns, and
multiplayer games (both networked and local).

@defvar {Scheme Variable} wesnothd-service-type
Service type for the wesnothd service.  Its value must be a
@code{wesnothd-configuration} object.  To run wesnothd in the default
configuration, instantiate it as:

@example
(service wesnothd-service-type)
@end example
@end defvar

@deftp {Data Type} wesnothd-configuration
Data type representing the configuration of @command{wesnothd}.

@table @asis
@item @code{package} (default: @code{wesnoth-server})
The wesnoth server package to use.

@item @code{port} (default: @code{15000})
The port to bind the server to.
@end table
@end deftp

@node Verschiedene Dienste
@subsubsection Verschiedene Dienste

@cindex fingerprint
@subsubheading Fingerprint Service

The @code{(gnu services fingerprint)} module provides a DBus service to read
and identify fingerprints via a fingerprint sensor.

@defvr {Scheme Variable} fprintd-service-type
The service type for @command{fprintd}, which provides the fingerprint
reading capability.

@example
(service fprintd-service-type)
@end example
@end defvr

@cindex sysctl
@subsubheading System Control Service

The @code{(gnu services sysctl)} provides a service to configure kernel
parameters at boot.

@defvr {Scheme Variable} sysctl-service-type
The service type for @command{sysctl}, which modifies kernel parameters
under @file{/proc/sys/}.  To enable IPv4 forwarding, it can be instantiated
as:

@example
(service sysctl-service-type
         (sysctl-configuration
           (settings '(("net.ipv4.ip_forward" . "1")))))
@end example
@end defvr

@deftp {Data Type} sysctl-configuration
The data type representing the configuration of @command{sysctl}.

@table @asis
@item @code{sysctl} (default: @code{(file-append procps "/sbin/sysctl"})
The @command{sysctl} executable to use.

@item @code{settings} (default: @code{'()})
An association list specifies kernel parameters and their values.
@end table
@end deftp

@cindex pcscd
@subsubheading PC/SC Smart Card Daemon Service

The @code{(gnu services security-token)} module provides the following
service to run @command{pcscd}, the PC/SC Smart Card Daemon.
@command{pcscd} is the daemon program for pcsc-lite and the MuscleCard
framework. It is a resource manager that coordinates communications with
smart card readers, smart cards and cryptographic tokens that are connected
to the system.

@defvr {Scheme Variable} pcscd-service-type
Service type for the @command{pcscd} service.  Its value must be a
@code{pcscd-configuration} object.  To run pcscd in the default
configuration, instantiate it as:

@example
(service pcscd-service-type)
@end example
@end defvr

@deftp {Data Type} pcscd-configuration
The data type representing the configuration of @command{pcscd}.

@table @asis
@item @code{pcsc-lite} (default: @code{pcsc-lite})
The pcsc-lite package that provides pcscd.
@item @code{usb-drivers} (default: @code{(list ccid)})
List of packages that provide USB drivers to pcscd. Drivers are expected to
be under @file{pcsc/drivers} in the store directory of the package.
@end table
@end deftp

@cindex lirc
@subsubheading Lirc Service

The @code{(gnu services lirc)} module provides the following service.

@deffn {Scheme Procedure} lirc-service [#:lirc lirc] @
       [#:device #f] [#:driver #f] [#:config-file #f] @ [#:extra-options '()]
Return a service that runs @url{http://www.lirc.org,LIRC}, a daemon that
decodes infrared signals from remote controls.

Optionally, @var{device}, @var{driver} and @var{config-file} (configuration
file name) may be specified.  See @command{lircd} manual for details.

Finally, @var{extra-options} is a list of additional command-line options
passed to @command{lircd}.
@end deffn

@cindex spice
@subsubheading Spice Service

The @code{(gnu services spice)} module provides the following service.

@deffn {Scheme Procedure} spice-vdagent-service [#:spice-vdagent]
Returns a service that runs @url{http://www.spice-space.org,VDAGENT}, a
daemon that enables sharing the clipboard with a vm and setting the guest
display resolution when the graphical console window resizes.
@end deffn

@subsubsection Dictionary Services
@cindex dictionary
The @code{(gnu services dict)} module provides the following service:

@deffn {Scheme Procedure} dicod-service [#:config (dicod-configuration)]
Return a service that runs the @command{dicod} daemon, an implementation of
DICT server (@pxref{Dicod,,, dico, GNU Dico Manual}).

The optional @var{config} argument specifies the configuration for
@command{dicod}, which should be a @code{<dicod-configuration>} object, by
default it serves the GNU Collaborative International Dictonary of English.

You can add @command{open localhost} to your @file{~/.dico} file to make
@code{localhost} the default server for @command{dico} client
(@pxref{Initialization File,,, dico, GNU Dico Manual}).
@end deffn

@deftp {Data Type} dicod-configuration
Data type representing the configuration of dicod.

@table @asis
@item @code{dico} (default: @var{dico})
Package object of the GNU Dico dictionary server.

@item @code{interfaces} (default: @var{'("localhost")})
This is the list of IP addresses and ports and possibly socket file names to
listen to (@pxref{Server Settings, @code{listen} directive,, dico, GNU Dico
Manual}).

@item @code{handlers} (default: @var{'()})
List of @code{<dicod-handler>} objects denoting handlers (module instances).

@item @code{databases} (default: @var{(list %dicod-database:gcide)})
List of @code{<dicod-database>} objects denoting dictionaries to be served.
@end table
@end deftp

@deftp {Data Type} dicod-handler
Data type representing a dictionary handler (module instance).

@table @asis
@item @code{name}
Name of the handler (module instance).

@item @code{module} (default: @var{#f})
Name of the dicod module of the handler (instance).  If it is @code{#f}, the
module has the same name as the handler.  (@pxref{Module,,, dico, GNU Dico
Manual}).

@item @code{options}
List of strings or gexps representing the arguments for the module handler
@end table
@end deftp

@deftp {Data Type} dicod-database
Data type representing a dictionary database.

@table @asis
@item @code{name}
Name of the database, will be used in DICT commands.

@item @code{handler}
Name of the dicod handler (module instance) used by this database
(@pxref{Handlers,,, dico, GNU Dico Manual}).

@item @code{complex?} (default: @var{#f})
Whether the database configuration complex.  The complex configuration will
need a corresponding @code{<dicod-handler>} object, otherwise not.

@item @code{options}
List of strings or gexps representing the arguments for the database
(@pxref{Databases,,, dico, GNU Dico Manual}).
@end table
@end deftp

@defvr {Scheme Variable} %dicod-database:gcide
A @code{<dicod-database>} object serving the GNU Collaborative International
Dictionary of English using the @code{gcide} package.
@end defvr

The following is an example @code{dicod-service} configuration.

@example
(dicod-service #:config
  (dicod-configuration
   (handlers (list (dicod-handler
                    (name "wordnet")
                    (module "dictorg")
                    (options
                     (list #~(string-append "dbdir=" #$wordnet))))))
   (databases (list (dicod-database
                     (name "wordnet")
                     (complex? #t)
                     (handler "wordnet")
                     (options '("database=wn")))
                    %dicod-database:gcide))))
@end example

@node Setuid-Programme
@subsection Setuid-Programme

@cindex setuid programs
Some programs need to run with ``root'' privileges, even when they are
launched by unprivileged users.  A notorious example is the @command{passwd}
program, which users can run to change their password, and which needs to
access the @file{/etc/passwd} and @file{/etc/shadow} files---something
normally restricted to root, for obvious security reasons.  To address that,
these executables are @dfn{setuid-root}, meaning that they always run with
root privileges (@pxref{How Change Persona,,, libc, The GNU C Library
Reference Manual}, for more info about the setuid mechanism.)

The store itself @emph{cannot} contain setuid programs: that would be a
security issue since any user on the system can write derivations that
populate the store (@pxref{Der Store}).  Thus, a different mechanism is
used: instead of changing the setuid bit directly on files that are in the
store, we let the system administrator @emph{declare} which programs should
be setuid root.

The @code{setuid-programs} field of an @code{operating-system} declaration
contains a list of G-expressions denoting the names of programs to be
setuid-root (@pxref{Das Konfigurationssystems nutzen}).  For instance, the
@command{passwd} program, which is part of the Shadow package, can be
designated by this G-expression (@pxref{G-Ausdrücke}):

@example
#~(string-append #$shadow "/bin/passwd")
@end example

A default set of setuid programs is defined by the @code{%setuid-programs}
variable of the @code{(gnu system)} module.

@defvr {Scheme Variable} %setuid-programs
A list of G-expressions denoting common programs that are setuid-root.

The list includes commands such as @command{passwd}, @command{ping},
@command{su}, and @command{sudo}.
@end defvr

Under the hood, the actual setuid programs are created in the
@file{/run/setuid-programs} directory at system activation time.  The files
in this directory refer to the ``real'' binaries, which are in the store.

@node X.509-Zertifikate
@subsection X.509-Zertifikate

@cindex HTTPS, certificates
@cindex X.509 certificates
@cindex TLS
Web servers available over HTTPS (that is, HTTP over the transport-layer
security mechanism, TLS) send client programs an @dfn{X.509 certificate}
that the client can then use to @emph{authenticate} the server.  To do that,
clients verify that the server's certificate is signed by a so-called
@dfn{certificate authority} (CA).  But to verify the CA's signature, clients
must have first acquired the CA's certificate.

Web browsers such as GNU@tie{}IceCat include their own set of CA
certificates, such that they are able to verify CA signatures
out-of-the-box.

However, most other programs that can talk HTTPS---@command{wget},
@command{git}, @command{w3m}, etc.---need to be told where CA certificates
can be found.

@cindex @code{nss-certs}
In GuixSD, this is done by adding a package that provides certificates to
the @code{packages} field of the @code{operating-system} declaration
(@pxref{„operating-system“-Referenz}).  GuixSD includes one such package,
@code{nss-certs}, which is a set of CA certificates provided as part of
Mozilla's Network Security Services.

Note that it is @emph{not} part of @var{%base-packages}, so you need to
explicitly add it.  The @file{/etc/ssl/certs} directory, which is where most
applications and libraries look for certificates by default, points to the
certificates installed globally.

Unprivileged users, including users of Guix on a foreign distro, can also
install their own certificate package in their profile.  A number of
environment variables need to be defined so that applications and libraries
know where to find them.  Namely, the OpenSSL library honors the
@code{SSL_CERT_DIR} and @code{SSL_CERT_FILE} variables.  Some applications
add their own environment variables; for instance, the Git version control
system honors the certificate bundle pointed to by the @code{GIT_SSL_CAINFO}
environment variable.  Thus, you would typically run something like:

@example
$ guix package -i nss-certs
$ export SSL_CERT_DIR="$HOME/.guix-profile/etc/ssl/certs"
$ export SSL_CERT_FILE="$HOME/.guix-profile/etc/ssl/certs/ca-certificates.crt"
$ export GIT_SSL_CAINFO="$SSL_CERT_FILE"
@end example

As another example, R requires the @code{CURL_CA_BUNDLE} environment
variable to point to a certificate bundle, so you would have to run
something like this:

@example
$ guix package -i nss-certs
$ export CURL_CA_BUNDLE="$HOME/.guix-profile/etc/ssl/certs/ca-certificates.crt"
@end example

For other applications you may want to look up the required environment
variable in the relevant documentation.


@node Name Service Switch
@subsection Name Service Switch

@cindex name service switch
@cindex NSS
The @code{(gnu system nss)} module provides bindings to the configuration
file of the libc @dfn{name service switch} or @dfn{NSS} (@pxref{NSS
Configuration File,,, libc, The GNU C Library Reference Manual}).  In a
nutshell, the NSS is a mechanism that allows libc to be extended with new
``name'' lookup methods for system databases, which includes host names,
service names, user accounts, and more (@pxref{Name Service Switch, System
Databases and Name Service Switch,, libc, The GNU C Library Reference
Manual}).

The NSS configuration specifies, for each system database, which lookup
method is to be used, and how the various methods are chained together---for
instance, under which circumstances NSS should try the next method in the
list.  The NSS configuration is given in the @code{name-service-switch}
field of @code{operating-system} declarations (@pxref{„operating-system“-Referenz, @code{name-service-switch}}).

@cindex nss-mdns
@cindex .local, host name lookup
As an example, the declaration below configures the NSS to use the
@uref{http://0pointer.de/lennart/projects/nss-mdns/, @code{nss-mdns}
back-end}, which supports host name lookups over multicast DNS (mDNS)  for
host names ending in @code{.local}:

@example
(name-service-switch
   (hosts (list %files    ;first, check /etc/hosts

                ;; If the above did not succeed, try
                ;; with 'mdns_minimal'.
                (name-service
                  (name "mdns_minimal")

                  ;; 'mdns_minimal' is authoritative for
                  ;; '.local'.  When it returns "not found",
                  ;; no need to try the next methods.
                  (reaction (lookup-specification
                             (not-found => return))))

                ;; Then fall back to DNS.
                (name-service
                  (name "dns"))

                ;; Finally, try with the "full" 'mdns'.
                (name-service
                  (name "mdns")))))
@end example

Do not worry: the @code{%mdns-host-lookup-nss} variable (see below)
contains this configuration, so you will not have to type it if all you want
is to have @code{.local} host lookup working.

Note that, in this case, in addition to setting the
@code{name-service-switch} of the @code{operating-system} declaration, you
also need to use @code{avahi-service} (@pxref{Netzwerkdienste,
@code{avahi-service}}), or @var{%desktop-services}, which includes it
(@pxref{Desktop-Dienste}).  Doing this makes @code{nss-mdns} accessible to
the name service cache daemon (@pxref{Basisdienste, @code{nscd-service}}).

For convenience, the following variables provide typical NSS configurations.

@defvr {Scheme Variable} %default-nss
This is the default name service switch configuration, a
@code{name-service-switch} object.
@end defvr

@defvr {Scheme Variable} %mdns-host-lookup-nss
This is the name service switch configuration with support for host name
lookup over multicast DNS (mDNS) for host names ending in @code{.local}.
@end defvr

The reference for name service switch configuration is given below.  It is a
direct mapping of the configuration file format of the C library , so please
refer to the C library manual for more information (@pxref{NSS Configuration
File,,, libc, The GNU C Library Reference Manual}).  Compared to the
configuration file format of libc NSS, it has the advantage not only of
adding this warm parenthetic feel that we like, but also static checks: you
will know about syntax errors and typos as soon as you run @command{guix
system}.

@deftp {Data Type} name-service-switch

This is the data type representation the configuration of libc's name
service switch (NSS).  Each field below represents one of the supported
system databases.

@table @code
@item aliases
@itemx ethers
@itemx group
@itemx gshadow
@itemx hosts
@itemx initgroups
@itemx netgroup
@itemx networks
@itemx password
@itemx public-key
@itemx rpc
@itemx services
@itemx shadow
The system databases handled by the NSS.  Each of these fields must be a
list of @code{<name-service>} objects (see below).
@end table
@end deftp

@deftp {Data Type} name-service

This is the data type representing an actual name service and the associated
lookup action.

@table @code
@item name
A string denoting the name service (@pxref{Services in the NSS
configuration,,, libc, The GNU C Library Reference Manual}).

Note that name services listed here must be visible to nscd.  This is
achieved by passing the @code{#:name-services} argument to
@code{nscd-service} the list of packages providing the needed name services
(@pxref{Basisdienste, @code{nscd-service}}).

@item reaction
An action specified using the @code{lookup-specification} macro
(@pxref{Actions in the NSS configuration,,, libc, The GNU C Library
Reference Manual}).  For example:

@example
(lookup-specification (unavailable => continue)
                      (success => return))
@end example
@end table
@end deftp

@node Initiale RAM-Disk
@subsection Initiale RAM-Disk

@cindex initrd
@cindex initial RAM disk
For bootstrapping purposes, the Linux-Libre kernel is passed an @dfn{initial
RAM disk}, or @dfn{initrd}.  An initrd contains a temporary root file system
as well as an initialization script.  The latter is responsible for mounting
the real root file system, and for loading any kernel modules that may be
needed to achieve that.

The @code{initrd-modules} field of an @code{operating-system} declaration
allows you to specify Linux-libre kernel modules that must be available in
the initrd.  In particular, this is where you would list modules needed to
actually drive the hard disk where your root partition is---although the
default value of @code{initrd-modules} should cover most use cases.  For
example, assuming you need the @code{megaraid_sas} module in addition to the
default modules to be able to access your root file system, you would write:

@example
(operating-system
  ;; @dots{}
  (initrd-modules (cons "megaraid_sas" %base-initrd-modules)))
@end example

@defvr {Scheme Variable} %base-initrd-modules
This is the list of kernel modules included in the initrd by default.
@end defvr

Furthermore, if you need lower-level customization, the @code{initrd} field
of an @code{operating-system} declaration allows you to specify which initrd
you would like to use.  The @code{(gnu system linux-initrd)} module provides
three ways to build an initrd: the high-level @code{base-initrd} procedure
and the low-level @code{raw-initrd} and @code{expression->initrd}
procedures.

The @code{base-initrd} procedure is intended to cover most common uses.  For
example, if you want to add a bunch of kernel modules to be loaded at boot
time, you can define the @code{initrd} field of the operating system
declaration like this:

@example
(initrd (lambda (file-systems . rest)
          ;; Create a standard initrd but set up networking
          ;; with the parameters QEMU expects by default.
          (apply base-initrd file-systems
                 #:qemu-networking? #t
                 rest)))
@end example

The @code{base-initrd} procedure also handles common use cases that involves
using the system as a QEMU guest, or as a ``live'' system with volatile root
file system.

The @code{base-initrd} procedure is built from @code{raw-initrd} procedure.
Unlike @code{base-initrd}, @code{raw-initrd} doesn't do anything high-level,
such as trying to guess which kernel modules and packages should be included
to the initrd. An example use of @code{raw-initrd} is when a user has a
custom Linux kernel configuration and default kernel modules included by
@code{base-initrd} are not available.

The initial RAM disk produced by @code{base-initrd} or @code{raw-initrd}
honors several options passed on the Linux kernel command line (that is,
arguments passed @i{via} the @code{linux} command of GRUB, or the
@code{-append} option of QEMU), notably:

@table @code
@item --load=@var{boot}
Tell the initial RAM disk to load @var{boot}, a file containing a Scheme
program, once it has mounted the root file system.

GuixSD uses this option to yield control to a boot program that runs the
service activation programs and then spawns the GNU@tie{}Shepherd, the
initialization system.

@item --root=@var{root}
Mount @var{root} as the root file system.  @var{root} can be a device name
like @code{/dev/sda1}, a file system label, or a file system UUID.

@item --system=@var{System}
Have @file{/run/booted-system} and @file{/run/current-system} point to
@var{system}.

@item modprobe.blacklist=@var{modules}@dots{}
@cindex module, black-listing
@cindex black list, of kernel modules
Instruct the initial RAM disk as well as the @command{modprobe} command
(from the kmod package) to refuse to load @var{modules}.  @var{modules} must
be a comma-separated list of module names---e.g., @code{usbkbd,9pnet}.

@item --repl
Start a read-eval-print loop (REPL) from the initial RAM disk before it
tries to load kernel modules and to mount the root file system.  Our
marketing team calls it @dfn{boot-to-Guile}.  The Schemer in you will love
it.  @xref{Using Guile Interactively,,, guile, GNU Guile Reference Manual},
for more information on Guile's REPL.

@end table

Now that you know all the features that initial RAM disks produced by
@code{base-initrd} and @code{raw-initrd} provide, here is how to use it and
customize it further.

@cindex initrd
@cindex initial RAM disk
@deffn {Monadic Procedure} raw-initrd @var{file-systems} @
       [#:linux-modules '()] [#:mapped-devices '()] @ [#:helper-packages '()]
[#:qemu-networking? #f] [#:volatile-root? #f] Return a monadic derivation
that builds a raw initrd.  @var{file-systems} is a list of file systems to
be mounted by the initrd, possibly in addition to the root file system
specified on the kernel command line via @code{--root}.  @var{linux-modules}
is a list of kernel modules to be loaded at boot time.  @var{mapped-devices}
is a list of device mappings to realize before @var{file-systems} are
mounted (@pxref{Abgebildete Geräte}).  @var{helper-packages} is a list of
packages to be copied in the initrd. It may include @code{e2fsck/static} or
other packages needed by the initrd to check the root file system.

When @var{qemu-networking?} is true, set up networking with the standard
QEMU parameters.  When @var{virtio?} is true, load additional modules so
that the initrd can be used as a QEMU guest with para-virtualized I/O
drivers.

When @var{volatile-root?} is true, the root file system is writable but any
changes to it are lost.
@end deffn

@deffn {Monadic Procedure} base-initrd @var{file-systems} @
       [#:mapped-devices '()] [#:qemu-networking? #f] [#:volatile-root? #f]@
[#:linux-modules '()] Return a monadic derivation that builds a generic
initrd, with kernel modules taken from @var{linux}.  @var{file-systems} is a
list of file-systems to be mounted by the initrd, possibly in addition to
the root file system specified on the kernel command line via
@code{--root}.  @var{mapped-devices} is a list of device mappings to realize
before @var{file-systems} are mounted.

@var{qemu-networking?} and @var{volatile-root?} behaves as in
@code{raw-initrd}.

The initrd is automatically populated with all the kernel modules necessary
for @var{file-systems} and for the given options.  Additional kernel modules
can be listed in @var{linux-modules}.  They will be added to the initrd, and
loaded at boot time in the order in which they appear.
@end deffn

Needless to say, the initrds we produce and use embed a statically-linked
Guile, and the initialization program is a Guile program.  That gives a lot
of flexibility.  The @code{expression->initrd} procedure builds such an
initrd, given the program to run in that initrd.

@deffn {Monadic Procedure} expression->initrd @var{exp} @
       [#:guile %guile-static-stripped] [#:name "guile-initrd"] Return a derivation
that builds a Linux initrd (a gzipped cpio archive)  containing @var{guile}
and that evaluates @var{exp}, a G-expression, upon booting.  All the
derivations referenced by @var{exp} are automatically copied to the initrd.
@end deffn

@node Bootloader-Konfiguration
@subsection Bootloader-Konfiguration

@cindex bootloader
@cindex boot loader

The operating system supports multiple bootloaders.  The bootloader is
configured using @code{bootloader-configuration} declaration.  All the
fields of this structure are bootloader agnostic except for one field,
@code{bootloader} that indicates the bootloader to be configured and
installed.

Some of the bootloaders do not honor every field of
@code{bootloader-configuration}.  For instance, the extlinux bootloader does
not support themes and thus ignores the @code{theme} field.

@deftp {Data Type} bootloader-configuration
The type of a bootloader configuration declaration.

@table @asis

@item @code{bootloader}
@cindex EFI, bootloader
@cindex UEFI, bootloader
@cindex BIOS, bootloader
The bootloader to use, as a @code{bootloader} object. For now
@code{grub-bootloader}, @code{grub-efi-bootloader},
@code{extlinux-bootloader} and @code{u-boot-bootloader} are supported.

@vindex grub-efi-bootloader
@code{grub-efi-bootloader} allows to boot on modern systems using the
@dfn{Unified Extensible Firmware Interface} (UEFI).  This is what you should
use if the installation image contains a @file{/sys/firmware/efi} directory
when you boot it on your system.

@vindex grub-bootloader
@code{grub-bootloader} allows you to boot in particular Intel-based machines
in ``legacy'' BIOS mode.

@cindex ARM, bootloaders
@cindex AArch64, bootloaders
Available bootloaders are described in @code{(gnu bootloader @dots{})}
modules.  In particular, @code{(gnu bootloader u-boot)} contains definitions
of bootloaders for a wide range of ARM and AArch64 systems, using the
@uref{http://www.denx.de/wiki/U-Boot/, U-Boot bootloader}.

@item @code{target}
This is a string denoting the target onto which to install the bootloader.

The interpretation depends on the bootloader in question.  For
@code{grub-bootloader}, for example, it should be a device name understood
by the bootloader @command{installer} command, such as @code{/dev/sda} or
@code{(hd0)} (@pxref{Invoking grub-install,,, grub, GNU GRUB Manual}).  For
@code{grub-efi-bootloader}, it should be the mount point of the EFI file
system, usually @file{/boot/efi}.

@item @code{menu-entries} (default: @code{()})
A possibly empty list of @code{menu-entry} objects (see below), denoting
entries to appear in the bootloader menu, in addition to the current system
entry and the entry pointing to previous system generations.

@item @code{default-entry} (default: @code{0})
The index of the default boot menu entry.  Index 0 is for the entry of the
current system.

@item @code{timeout} (default: @code{5})
The number of seconds to wait for keyboard input before booting.  Set to 0
to boot immediately, and to -1 to wait indefinitely.

@item @code{theme} (default: @var{#f})
The bootloader theme object describing the theme to use.  If no theme is
provided, some bootloaders might use a default theme, that's true for GRUB.

@item @code{terminal-outputs} (default: @code{'gfxterm})
The output terminals used for the bootloader boot menu, as a list of
symbols.  GRUB accepts the values: @code{console}, @code{serial},
@code{serial_@{0-3@}}, @code{gfxterm}, @code{vga_text}, @code{mda_text},
@code{morse}, and @code{pkmodem}.  This field corresponds to the GRUB
variable @code{GRUB_TERMINAL_OUTPUT} (@pxref{Simple configuration,,,
grub,GNU GRUB manual}).

@item @code{terminal-inputs} (default: @code{'()})
The input terminals used for the bootloader boot menu, as a list of
symbols.  For GRUB, the default is the native platform terminal as
determined at run-time.  GRUB accepts the values: @code{console},
@code{serial}, @code{serial_@{0-3@}}, @code{at_keyboard}, and
@code{usb_keyboard}.  This field corresponds to the GRUB variable
@code{GRUB_TERMINAL_INPUT} (@pxref{Simple configuration,,, grub,GNU GRUB
manual}).

@item @code{serial-unit} (default: @code{#f})
The serial unit used by the bootloader, as an integer from 0 to 3.  For
GRUB, it is chosen at run-time; currently GRUB chooses 0, which corresponds
to COM1 (@pxref{Serial terminal,,, grub,GNU GRUB manual}).

@item @code{serial-speed} (default: @code{#f})
The speed of the serial interface, as an integer.  For GRUB, the default
value is chosen at run-time; currently GRUB chooses 9600@tie{}bps
(@pxref{Serial terminal,,, grub,GNU GRUB manual}).
@end table

@end deftp

@cindex dual boot
@cindex boot menu
Should you want to list additional boot menu entries @i{via} the
@code{menu-entries} field above, you will need to create them with the
@code{menu-entry} form.  For example, imagine you want to be able to boot
another distro (hard to imagine!), you can define a menu entry along these
lines:

@example
(menu-entry
  (label "The Other Distro")
  (linux "/boot/old/vmlinux-2.6.32")
  (linux-arguments '("root=/dev/sda2"))
  (initrd "/boot/old/initrd"))
@end example

Details below.

@deftp {Data Type} menu-entry
The type of an entry in the bootloader menu.

@table @asis

@item @code{label}
The label to show in the menu---e.g., @code{"GNU"}.

@item @code{linux}
The Linux kernel image to boot, for example:

@example
(file-append linux-libre "/bzImage")
@end example

For GRUB, it is also possible to specify a device explicitly in the file
path using GRUB's device naming convention (@pxref{Naming convention,,,
grub, GNU GRUB manual}), for example:

@example
"(hd0,msdos1)/boot/vmlinuz"
@end example

If the device is specified explicitly as above, then the @code{device} field
is ignored entirely.

@item @code{linux-arguments} (default: @code{()})
The list of extra Linux kernel command-line arguments---e.g.,
@code{("console=ttyS0")}.

@item @code{initrd}
A G-Expression or string denoting the file name of the initial RAM disk to
use (@pxref{G-Ausdrücke}).
@item @code{device} (default: @code{#f})
The device where the kernel and initrd are to be found---i.e., for GRUB,
@dfn{root} for this menu entry (@pxref{root,,, grub, GNU GRUB manual}).

This may be a file system label (a string), a file system UUID (a
bytevector, @pxref{Dateisysteme}), or @code{#f}, in which case the
bootloader will search the device containing the file specified by the
@code{linux} field (@pxref{search,,, grub, GNU GRUB manual}).  It must
@emph{not} be an OS device name such as @file{/dev/sda1}.

@end table
@end deftp

@c FIXME: Write documentation once it's stable.
Fow now only GRUB has theme support. GRUB themes are created using the
@code{grub-theme} form, which is not documented yet.

@defvr {Scheme Variable} %default-theme
This is the default GRUB theme used by the operating system if no
@code{theme} field is specified in @code{bootloader-configuration} record.

It comes with a fancy background image displaying the GNU and Guix logos.
@end defvr


@node Aufruf von guix system
@subsection Invoking @code{guix system}

Once you have written an operating system declaration as seen in the
previous section, it can be @dfn{instantiated} using the @command{guix
system} command.  The synopsis is:

@example
guix system @var{options}@dots{} @var{action} @var{file}
@end example

@var{file} must be the name of a file containing an @code{operating-system}
declaration.  @var{action} specifies how the operating system is
instantiated.  Currently the following values are supported:

@table @code
@item search
Display available service type definitions that match the given regular
expressions, sorted by relevance:

@example
$ guix system search console font
name: console-fonts
location: gnu/services/base.scm:729:2
extends: shepherd-root
description: Install the given fonts on the specified ttys (fonts are
+ per virtual console on GNU/Linux).  The value of this service is a list
+ of tty/font pairs like:
+ 
+      '(("tty1" . "LatGrkCyr-8x16"))
relevance: 20

name: mingetty
location: gnu/services/base.scm:1048:2
extends: shepherd-root
description: Provide console login using the `mingetty' program.
relevance: 2

name: login
location: gnu/services/base.scm:775:2
extends: pam
description: Provide a console log-in service as specified by its
+ configuration value, a `login-configuration' object.
relevance: 2

@dots{}
@end example

As for @command{guix package --search}, the result is written in
@code{recutils} format, which makes it easy to filter the output
(@pxref{Top, GNU recutils databases,, recutils, GNU recutils manual}).

@item reconfigure
Build the operating system described in @var{file}, activate it, and switch
to it@footnote{This action (and the related actions @code{switch-generation}
and @code{roll-back}) are usable only on systems already running GuixSD.}.

This effects all the configuration specified in @var{file}: user accounts,
system services, global package list, setuid programs, etc.  The command
starts system services specified in @var{file} that are not currently
running; if a service is currently running this command will arrange for it
to be upgraded the next time it is stopped (eg. by @code{herd stop X} or
@code{herd restart X}).

This command creates a new generation whose number is one greater than the
current generation (as reported by @command{guix system list-generations}).
If that generation already exists, it will be overwritten.  This behavior
mirrors that of @command{guix package} (@pxref{Aufruf von guix package}).

It also adds a bootloader menu entry for the new OS configuration, ---unless
@option{--no-bootloader} is passed.  For GRUB, it moves entries for older
configurations to a submenu, allowing you to choose an older system
generation at boot time should you need it.

@quotation Anmerkung
@c The paragraph below refers to the problem discussed at
@c <http://lists.gnu.org/archive/html/guix-devel/2014-08/msg00057.html>.
It is highly recommended to run @command{guix pull} once before you run
@command{guix system reconfigure} for the first time (@pxref{Aufruf von guix pull}).  Failing to do that you would see an older version of Guix once
@command{reconfigure} has completed.
@end quotation

@item switch-generation
@cindex Generationen
Switch to an existing system generation.  This action atomically switches
the system profile to the specified system generation.  It also rearranges
the system's existing bootloader menu entries.  It makes the menu entry for
the specified system generation the default, and it moves the entries for
the other generatiors to a submenu, if supported by the bootloader being
used.  The next time the system boots, it will use the specified system
generation.

The bootloader itself is not being reinstalled when using this command.
Thus, the installed bootloader is used with an updated configuration file.

The target generation can be specified explicitly by its generation number.
For example, the following invocation would switch to system generation 7:

@example
guix system switch-generation 7
@end example

The target generation can also be specified relative to the current
generation with the form @code{+N} or @code{-N}, where @code{+3} means ``3
generations ahead of the current generation,'' and @code{-1} means ``1
generation prior to the current generation.'' When specifying a negative
value such as @code{-1}, you must precede it with @code{--} to prevent it
from being parsed as an option.  For example:

@example
guix system switch-generation -- -1
@end example

Currently, the effect of invoking this action is @emph{only} to switch the
system profile to an existing generation and rearrange the bootloader menu
entries.  To actually start using the target system generation, you must
reboot after running this action.  In the future, it will be updated to do
the same things as @command{reconfigure}, like activating and deactivating
services.

This action will fail if the specified generation does not exist.

@item roll-back
@cindex rücksetzen
Switch to the preceding system generation.  The next time the system boots,
it will use the preceding system generation.  This is the inverse of
@command{reconfigure}, and it is exactly the same as invoking
@command{switch-generation} with an argument of @code{-1}.

Currently, as with @command{switch-generation}, you must reboot after
running this action to actually start using the preceding system generation.

@item build
Build the derivation of the operating system, which includes all the
configuration files and programs needed to boot and run the system.  This
action does not actually install anything.

@item init
Populate the given directory with all the files necessary to run the
operating system specified in @var{file}.  This is useful for first-time
installations of GuixSD.  For instance:

@example
guix system init my-os-config.scm /mnt
@end example

copies to @file{/mnt} all the store items required by the configuration
specified in @file{my-os-config.scm}.  This includes configuration files,
packages, and so on.  It also creates other essential files needed for the
system to operate correctly---e.g., the @file{/etc}, @file{/var}, and
@file{/run} directories, and the @file{/bin/sh} file.

This command also installs bootloader on the target specified in
@file{my-os-config}, unless the @option{--no-bootloader} option was passed.

@item vm
@cindex virtual machine
@cindex VM
@anchor{guix system vm}
Build a virtual machine that contains the operating system declared in
@var{file}, and return a script to run that virtual machine (VM).  Arguments
given to the script are passed to QEMU as in the example below, which
enables networking and requests 1@tie{}GiB of RAM for the emulated machine:

@example
$ /gnu/store/@dots{}-run-vm.sh -m 1024 -net user
@end example

The VM shares its store with the host system.

Additional file systems can be shared between the host and the VM using the
@code{--share} and @code{--expose} command-line options: the former
specifies a directory to be shared with write access, while the latter
provides read-only access to the shared directory.

The example below creates a VM in which the user's home directory is
accessible read-only, and where the @file{/exchange} directory is a
read-write mapping of @file{$HOME/tmp} on the host:

@example
guix system vm my-config.scm \
   --expose=$HOME --share=$HOME/tmp=/exchange
@end example

On GNU/Linux, the default is to boot directly to the kernel; this has the
advantage of requiring only a very tiny root disk image since the store of
the host can then be mounted.

The @code{--full-boot} option forces a complete boot sequence, starting with
the bootloader.  This requires more disk space since a root image containing
at least the kernel, initrd, and bootloader data files must be created.  The
@code{--image-size} option can be used to specify the size of the image.

@cindex System images, creation in various formats
@cindex Creating system images in various formats
@item vm-image
@itemx disk-image
@itemx docker-image
Return a virtual machine, disk image, or Docker image of the operating
system declared in @var{file} that stands alone.  By default, @command{guix
system} estimates the size of the image needed to store the system, but you
can use the @option{--image-size} option to specify a value.  Docker images
are built to contain exactly what they need, so the @option{--image-size}
option is ignored in the case of @code{docker-image}.

You can specify the root file system type by using the
@option{--file-system-type} option.  It defaults to @code{ext4}.

When using @code{vm-image}, the returned image is in qcow2 format, which the
QEMU emulator can efficiently use. @xref{GuixSD in einer VM starten}, for more
information on how to run the image in a virtual machine.

When using @code{disk-image}, a raw disk image is produced; it can be copied
as is to a USB stick, for instance.  Assuming @code{/dev/sdc} is the device
corresponding to a USB stick, one can copy the image to it using the
following command:

@example
# dd if=$(guix system disk-image my-os.scm) of=/dev/sdc
@end example

When using @code{docker-image}, a Docker image is produced.  Guix builds the
image from scratch, not from a pre-existing Docker base image.  As a result,
it contains @emph{exactly} what you define in the operating system
configuration file.  You can then load the image and launch a Docker
container using commands like the following:

@example
image_id="$(docker load < guixsd-docker-image.tar.gz)"
docker run -e GUIX_NEW_SYSTEM=/var/guix/profiles/system \\
    --entrypoint /var/guix/profiles/system/profile/bin/guile \\
    $image_id /var/guix/profiles/system/boot
@end example

This command starts a new Docker container from the specified image.  It
will boot the GuixSD system in the usual manner, which means it will start
any services you have defined in the operating system configuration.
Depending on what you run in the Docker container, it may be necessary to
give the container additional permissions.  For example, if you intend to
build software using Guix inside of the Docker container, you may need to
pass the @option{--privileged} option to @code{docker run}.

@item container
Return a script to run the operating system declared in @var{file} within a
container.  Containers are a set of lightweight isolation mechanisms
provided by the kernel Linux-libre.  Containers are substantially less
resource-demanding than full virtual machines since the kernel, shared
objects, and other resources can be shared with the host system; this also
means they provide thinner isolation.

Currently, the script must be run as root in order to support more than a
single user and group.  The container shares its store with the host system.

As with the @code{vm} action (@pxref{guix system vm}), additional file
systems to be shared between the host and container can be specified using
the @option{--share} and @option{--expose} options:

@example
guix system container my-config.scm \
   --expose=$HOME --share=$HOME/tmp=/exchange
@end example

@quotation Anmerkung
This option requires Linux-libre 3.19 or newer.
@end quotation

@end table

@var{options} can contain any of the common build options (@pxref{Gemeinsame Erstellungsoptionen}).  In addition, @var{options} can contain one of the
following:

@table @option
@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the operating-system @var{expr} evaluates to.  This is an
alternative to specifying a file which evaluates to an operating system.
This is used to generate the GuixSD installer @pxref{Ein Abbild zur Installation erstellen}).

@item --system=@var{System}
@itemx -s @var{system}
Attempt to build for @var{system} instead of the host system type.  This
works as per @command{guix build} (@pxref{Aufruf von guix build}).

@item --derivation
@itemx -d
Return the derivation file name of the given operating system without
building anything.

@item --file-system-type=@var{type}
@itemx -t @var{type}
For the @code{disk-image} action, create a file system of the given
@var{type} on the image.

When this option is omitted, @command{guix system} uses @code{ext4}.

@cindex ISO-9660 format
@cindex CD image format
@cindex DVD image format
@code{--file-system-type=iso9660} produces an ISO-9660 image, suitable for
burning on CDs and DVDs.

@item --image-size=@var{size}
For the @code{vm-image} and @code{disk-image} actions, create an image of
the given @var{size}.  @var{size} may be a number of bytes, or it may
include a unit as a suffix (@pxref{Block size, size specifications,,
coreutils, GNU Coreutils}).

When this option is omitted, @command{guix system} computes an estimate of
the image size as a function of the size of the system declared in
@var{file}.

@item --root=@var{file}
@itemx -r @var{file}
Make @var{file} a symlink to the result, and register it as a garbage
collector root.

@item --skip-checks
Skip pre-installation safety checks.

By default, @command{guix system init} and @command{guix system reconfigure}
perform safety checks: they make sure the file systems that appear in the
@code{operating-system} declaration actually exist (@pxref{Dateisysteme}),
and that any Linux kernel modules that may be needed at boot time are listed
in @code{initrd-modules} (@pxref{Initiale RAM-Disk}).  Passing this option
skips these tests altogether.

@item --on-error=@var{strategy}
Apply @var{strategy} when an error occurs when reading @var{file}.
@var{strategy} may be one of the following:

@table @code
@item nothing-special
Report the error concisely and exit.  This is the default strategy.

@item backtrace
Likewise, but also display a backtrace.

@item debug
Report the error and enter Guile's debugger.  From there, you can run
commands such as @code{,bt} to get a backtrace, @code{,locals} to display
local variable values, and more generally inspect the state of the program.
@xref{Debug Commands,,, guile, GNU Guile Reference Manual}, for a list of
available debugging commands.
@end table
@end table

@quotation Anmerkung
All the actions above, except @code{build} and @code{init}, can use KVM
support in the Linux-libre kernel.  Specifically, if the machine has
hardware virtualization support, the corresponding KVM kernel module should
be loaded, and the @file{/dev/kvm} device node must exist and be readable
and writable by the user and by the build users of the daemon (@pxref{Einrichten der Erstellungsumgebung}).
@end quotation

Once you have built, configured, re-configured, and re-re-configured your
GuixSD installation, you may find it useful to list the operating system
generations available on disk---and that you can choose from the bootloader
boot menu:

@table @code

@item list-generations
List a summary of each generation of the operating system available on disk,
in a human-readable way.  This is similar to the @option{--list-generations}
option of @command{guix package} (@pxref{Aufruf von guix package}).

Optionally, one can specify a pattern, with the same syntax that is used in
@command{guix package --list-generations}, to restrict the list of
generations displayed.  For instance, the following command displays
generations that are up to 10 days old:

@example
$ guix system list-generations 10d
@end example

@end table

The @command{guix system} command has even more to offer! The following
sub-commands allow you to visualize how your system services relate to each
other:

@anchor{system-extension-graph}
@table @code

@item extension-graph
Emit in Dot/Graphviz format to standard output the @dfn{service extension
graph} of the operating system defined in @var{file} (@pxref{Dienstkompositionen}, for more information on service extensions.)

The command:

@example
$ guix system extension-graph @var{file} | dot -Tpdf > services.pdf
@end example

produces a PDF file showing the extension relations among services.

@anchor{system-shepherd-graph}
@item shepherd-graph
Emit in Dot/Graphviz format to standard output the @dfn{dependency graph} of
shepherd services of the operating system defined in @var{file}.
@xref{Shepherd-Dienste}, for more information and for an example graph.

@end table

@node GuixSD in einer VM starten
@subsection Running GuixSD in a Virtual Machine

@cindex virtual machine
To run GuixSD in a virtual machine (VM), one can either use the pre-built
GuixSD VM image distributed at
@indicateurl{https://alpha.gnu.org/gnu/guix/guixsd-vm-image-@value{VERSION}.@var{system}.xz}
, or build their own virtual machine image using @command{guix system
vm-image} (@pxref{Aufruf von guix system}).  The returned image is in qcow2
format, which the @uref{http://qemu.org/, QEMU emulator} can efficiently
use.

@cindex QEMU
If you built your own image, you must copy it out of the store (@pxref{Der Store}) and give yourself permission to write to the copy before you can use
it.  When invoking QEMU, you must choose a system emulator that is suitable
for your hardware platform.  Here is a minimal QEMU invocation that will
boot the result of @command{guix system vm-image} on x86_64 hardware:

@example
$ qemu-system-x86_64 \
   -net user -net nic,model=virtio \
   -enable-kvm -m 256 /tmp/qemu-image
@end example

Here is what each of these options means:

@table @code
@item qemu-system-x86_64
This specifies the hardware platform to emulate.  This should match the
host.

@item -net user
Enable the unprivileged user-mode network stack.  The guest OS can access
the host but not vice versa.  This is the simplest way to get the guest OS
online.

@item -net nic,model=virtio
You must create a network interface of a given model.  If you do not create
a NIC, the boot will fail.  Assuming your hardware platform is x86_64, you
can get a list of available NIC models by running
@command{qemu-system-x86_64 -net nic,model=help}.

@item -enable-kvm
If your system has hardware virtualization extensions, enabling the virtual
machine support (KVM) of the Linux kernel will make things run faster.

@item -m 256
RAM available to the guest OS, in mebibytes.  Defaults to 128@tie{}MiB,
which may be insufficient for some operations.

@item /tmp/qemu-image
The file name of the qcow2 image.
@end table

The default @command{run-vm.sh} script that is returned by an invocation of
@command{guix system vm} does not add a @command{-net user} flag by
default.  To get network access from within the vm add the
@code{(dhcp-client-service)} to your system definition and start the VM
using @command{`guix system vm config.scm` -net user}.  An important caveat
of using @command{-net user} for networking is that @command{ping} will not
work, because it uses the ICMP protocol.  You'll have to use a different
command to check for network connectivity, for example @command{guix
download}.

@subsubsection Connecting Through SSH

@cindex SSH
@cindex SSH server
To enable SSH inside a VM you need to add a SSH server like
@code{(dropbear-service)} or @code{(lsh-service)} to your VM.  The
@code{(lsh-service}) doesn't currently boot unsupervised.  It requires you
to type some characters to initialize the randomness generator.  In addition
you need to forward the SSH port, 22 by default, to the host.  You can do
this with

@example
`guix system vm config.scm` -net user,hostfwd=tcp::10022-:22
@end example

To connect to the VM you can run

@example
ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -p 10022
@end example

The @command{-p} tells @command{ssh} the port you want to connect to.
@command{-o UserKnownHostsFile=/dev/null} prevents @command{ssh} from
complaining every time you modify your @command{config.scm} file and the
@command{-o StrictHostKeyChecking=no} prevents you from having to allow a
connection to an unknown host every time you connect.

@subsubsection Using @command{virt-viewer} with Spice

As an alternative to the default @command{qemu} graphical client you can use
the @command{remote-viewer} from the @command{virt-viewer} package.  To
connect pass the @command{-spice port=5930,disable-ticketing} flag to
@command{qemu}.  See previous section for further information on how to do
this.

Spice also allows you to do some nice stuff like share your clipboard with
your VM.  To enable that you'll also have to pass the following flags to
@command{qemu}:

@example
-device virtio-serial-pci,id=virtio-serial0,max_ports=16,bus=pci.0,addr=0x5
-chardev spicevmc,name=vdagent,id=vdagent
-device virtserialport,nr=1,bus=virtio-serial0.0,chardev=vdagent,
name=com.redhat.spice.0
@end example

You'll also need to add the @pxref{Verschiedene Dienste, Spice service}.

@node Dienste definieren
@subsection Dienste definieren

The previous sections show the available services and how one can combine
them in an @code{operating-system} declaration.  But how do we define them
in the first place? And what is a service anyway?

@menu
* Dienstkompositionen::      Wie Dienste zusammengestellt werden.
* Diensttypen und Dienste::  Typen und Dienste.
* Service-Referenz::         Referenz zur Programmierschnittstelle
* Shepherd-Dienste::         Eine spezielle Art von Dienst.
@end menu

@node Dienstkompositionen
@subsubsection Dienstkompositionen

@cindex services
@cindex daemons
Here we define a @dfn{service} as, broadly, something that extends the
functionality of the operating system.  Often a service is a process---a
@dfn{daemon}---started when the system boots: a secure shell server, a Web
server, the Guix build daemon, etc.  Sometimes a service is a daemon whose
execution can be triggered by another daemon---e.g., an FTP server started
by @command{inetd} or a D-Bus service activated by @command{dbus-daemon}.
Occasionally, a service does not map to a daemon.  For instance, the
``account'' service collects user accounts and makes sure they exist when
the system runs; the ``udev'' service collects device management rules and
makes them available to the eudev daemon; the @file{/etc} service populates
the @file{/etc} directory of the system.

@cindex service extensions
GuixSD services are connected by @dfn{extensions}.  For instance, the secure
shell service @emph{extends} the Shepherd---the GuixSD initialization
system, running as PID@tie{}1---by giving it the command lines to start and
stop the secure shell daemon (@pxref{Netzwerkdienste,
@code{lsh-service}}); the UPower service extends the D-Bus service by
passing it its @file{.service} specification, and extends the udev service
by passing it device management rules (@pxref{Desktop-Dienste,
@code{upower-service}}); the Guix daemon service extends the Shepherd by
passing it the command lines to start and stop the daemon, and extends the
account service by passing it a list of required build user accounts
(@pxref{Basisdienste}).

All in all, services and their ``extends'' relations form a directed acyclic
graph (DAG).  If we represent services as boxes and extensions as arrows, a
typical system might provide something like this:

@image{images/service-graph,,5in,Typical service extension graph.}

@cindex system service
At the bottom, we see the @dfn{system service}, which produces the directory
containing everything to run and boot the system, as returned by the
@command{guix system build} command.  @xref{Service-Referenz}, to learn
about the other service types shown here.  @xref{system-extension-graph, the
@command{guix system extension-graph} command}, for information on how to
generate this representation for a particular operating system definition.

@cindex service types
Technically, developers can define @dfn{service types} to express these
relations.  There can be any number of services of a given type on the
system---for instance, a system running two instances of the GNU secure
shell server (lsh) has two instances of @var{lsh-service-type}, with
different parameters.

The following section describes the programming interface for service types
and services.

@node Diensttypen und Dienste
@subsubsection Diensttypen und Dienste

A @dfn{service type} is a node in the DAG described above.  Let us start
with a simple example, the service type for the Guix build daemon
(@pxref{Aufruf des guix-daemon}):

@example
(define guix-service-type
  (service-type
   (name 'guix)
   (extensions
    (list (service-extension shepherd-root-service-type guix-shepherd-service)
          (service-extension account-service-type guix-accounts)
          (service-extension activation-service-type guix-activation)))
   (default-value (guix-configuration))))
@end example

@noindent
It defines three things:

@enumerate
@item
A name, whose sole purpose is to make inspection and debugging easier.

@item
A list of @dfn{service extensions}, where each extension designates the
target service type and a procedure that, given the parameters of the
service, returns a list of objects to extend the service of that type.

Every service type has at least one service extension.  The only exception
is the @dfn{boot service type}, which is the ultimate service.

@item
Optionally, a default value for instances of this type.
@end enumerate

In this example, @var{guix-service-type} extends three services:

@table @var
@item shepherd-root-service-type
The @var{guix-shepherd-service} procedure defines how the Shepherd service
is extended.  Namely, it returns a @code{<shepherd-service>} object that
defines how @command{guix-daemon} is started and stopped (@pxref{Shepherd-Dienste}).

@item account-service-type
This extension for this service is computed by @var{guix-accounts}, which
returns a list of @code{user-group} and @code{user-account} objects
representing the build user accounts (@pxref{Aufruf des guix-daemon}).

@item activation-service-type
Here @var{guix-activation} is a procedure that returns a gexp, which is a
code snippet to run at ``activation time''---e.g., when the service is
booted.
@end table

A service of this type is instantiated like this:

@example
(service guix-service-type
         (guix-configuration
           (build-accounts 5)
           (use-substitutes? #f)))
@end example

The second argument to the @code{service} form is a value representing the
parameters of this specific service instance.
@xref{guix-configuration-type, @code{guix-configuration}}, for information
about the @code{guix-configuration} data type.  When the value is omitted,
the default value specified by @code{guix-service-type} is used:

@example
(service guix-service-type)
@end example

@var{guix-service-type} is quite simple because it extends other services
but is not extensible itself.

@c @subsubsubsection Extensible Service Types

The service type for an @emph{extensible} service looks like this:

@example
(define udev-service-type
  (service-type (name 'udev)
                (extensions
                 (list (service-extension shepherd-root-service-type
                                          udev-shepherd-service)))

                (compose concatenate)       ;concatenate the list of rules
                (extend (lambda (config rules)
                          (match config
                            (($ <udev-configuration> udev initial-rules)
                             (udev-configuration
                              (udev udev)   ;the udev package to use
                              (rules (append initial-rules rules)))))))))
@end example

This is the service type for the
@uref{https://wiki.gentoo.org/wiki/Project:Eudev, eudev device management
daemon}.  Compared to the previous example, in addition to an extension of
@var{shepherd-root-service-type}, we see two new fields:

@table @code
@item compose
This is the procedure to @dfn{compose} the list of extensions to services of
this type.

Services can extend the udev service by passing it lists of rules; we
compose those extensions simply by concatenating them.

@item extend
This procedure defines how the value of the service is @dfn{extended} with
the composition of the extensions.

Udev extensions are composed into a list of rules, but the udev service
value is itself a @code{<udev-configuration>} record.  So here, we extend
that record by appending the list of rules it contains to the list of
contributed rules.

@item description
This is a string giving an overview of the service type.  The string can
contain Texinfo markup (@pxref{Overview,,, texinfo, GNU Texinfo}).  The
@command{guix system search} command searches these strings and displays
them (@pxref{Aufruf von guix system}).
@end table

There can be only one instance of an extensible service type such as
@var{udev-service-type}.  If there were more, the @code{service-extension}
specifications would be ambiguous.

Still here? The next section provides a reference of the programming
interface for services.

@node Service-Referenz
@subsubsection Service-Referenz

We have seen an overview of service types (@pxref{Diensttypen und Dienste}).  This section provides a reference on how to manipulate services
and service types.  This interface is provided by the @code{(gnu services)}
module.

@deffn {Scheme Procedure} service @var{type} [@var{value}]
Return a new service of @var{type}, a @code{<service-type>} object (see
below.)  @var{value} can be any object; it represents the parameters of this
particular service instance.

When @var{value} is omitted, the default value specified by @var{type} is
used; if @var{type} does not specify a default value, an error is raised.

For instance, this:

@example
(service openssh-service-type)
@end example

@noindent
is equivalent to this:

@example
(service openssh-service-type
         (openssh-configuration))
@end example

In both cases the result is an instance of @code{openssh-service-type} with
the default configuration.
@end deffn

@deffn {Scheme Procedure} service? @var{obj}
Return true if @var{obj} is a service.
@end deffn

@deffn {Scheme Procedure} service-kind @var{service}
Return the type of @var{service}---i.e., a @code{<service-type>} object.
@end deffn

@deffn {Scheme Procedure} service-value @var{service}
Return the value associated with @var{service}.  It represents its
parameters.
@end deffn

Here is an example of how a service is created and manipulated:

@example
(define s
  (service nginx-service-type
           (nginx-configuration
            (nginx nginx)
            (log-directory log-directory)
            (run-directory run-directory)
            (file config-file))))

(service? s)
@result{} #t

(eq? (service-kind s) nginx-service-type)
@result{} #t
@end example

The @code{modify-services} form provides a handy way to change the
parameters of some of the services of a list such as @var{%base-services}
(@pxref{Basisdienste, @code{%base-services}}).  It evaluates to a list of
services.  Of course, you could always use standard list combinators such as
@code{map} and @code{fold} to do that (@pxref{SRFI-1, List Library,, guile,
GNU Guile Reference Manual}); @code{modify-services} simply provides a more
concise form for this common pattern.

@deffn {Scheme Syntax} modify-services @var{services} @
  (@var{type} @var{variable} => @var{body}) @dots{}

Modify the services listed in @var{services} according to the given
clauses.  Each clause has the form:

@example
(@var{type} @var{variable} => @var{body})
@end example

where @var{type} is a service type---e.g., @code{guix-service-type}---and
@var{variable} is an identifier that is bound within the @var{body} to the
service parameters---e.g., a @code{guix-configuration} instance---of the
original service of that @var{type}.

The @var{body} should evaluate to the new service parameters, which will be
used to configure the new service.  This new service will replace the
original in the resulting list.  Because a service's service parameters are
created using @code{define-record-type*}, you can write a succinct
@var{body} that evaluates to the new service parameters by using the
@code{inherit} feature that @code{define-record-type*} provides.

@xref{Das Konfigurationssystems nutzen}, for example usage.

@end deffn

Next comes the programming interface for service types.  This is something
you want to know when writing new service definitions, but not necessarily
when simply looking for ways to customize your @code{operating-system}
declaration.

@deftp {Data Type} service-type
@cindex service type
This is the representation of a @dfn{service type} (@pxref{Diensttypen und Dienste}).

@table @asis
@item @code{name}
This is a symbol, used only to simplify inspection and debugging.

@item @code{extensions}
A non-empty list of @code{<service-extension>} objects (see below).

@item @code{compose} (default: @code{#f})
If this is @code{#f}, then the service type denotes services that cannot be
extended---i.e., services that do not receive ``values'' from other
services.

Otherwise, it must be a one-argument procedure.  The procedure is called by
@code{fold-services} and is passed a list of values collected from
extensions.  It may return any single value.

@item @code{extend} (default: @code{#f})
If this is @code{#f}, services of this type cannot be extended.

Otherwise, it must be a two-argument procedure: @code{fold-services} calls
it, passing it the initial value of the service as the first argument and
the result of applying @code{compose} to the extension values as the second
argument.  It must return a value that is a valid parameter value for the
service instance.
@end table

@xref{Diensttypen und Dienste}, for examples.
@end deftp

@deffn {Scheme Procedure} service-extension @var{target-type} @
                              @var{compute} Return a new extension for services of type
@var{target-type}.  @var{compute} must be a one-argument procedure:
@code{fold-services} calls it, passing it the value associated with the
service that provides the extension; it must return a valid value for the
target service.
@end deffn

@deffn {Scheme Procedure} service-extension? @var{obj}
Return true if @var{obj} is a service extension.
@end deffn

Occasionally, you might want to simply extend an existing service.  This
involves creating a new service type and specifying the extension of
interest, which can be verbose; the @code{simple-service} procedure provides
a shorthand for this.

@deffn {Scheme Procedure} simple-service @var{name} @var{target} @var{value}
Return a service that extends @var{target} with @var{value}.  This works by
creating a singleton service type @var{name}, of which the returned service
is an instance.

For example, this extends mcron (@pxref{Geplante Auftragsausführung}) with an
additional job:

@example
(simple-service 'my-mcron-job mcron-service-type
                #~(job '(next-hour (3)) "guix gc -F 2G"))
@end example
@end deffn

At the core of the service abstraction lies the @code{fold-services}
procedure, which is responsible for ``compiling'' a list of services down to
a single directory that contains everything needed to boot and run the
system---the directory shown by the @command{guix system build} command
(@pxref{Aufruf von guix system}).  In essence, it propagates service
extensions down the service graph, updating each node parameters on the way,
until it reaches the root node.

@deffn {Scheme Procedure} fold-services @var{services} @
                            [#:target-type @var{system-service-type}] Fold @var{services} by propagating
their extensions down to the root of type @var{target-type}; return the root
service adjusted accordingly.
@end deffn

Lastly, the @code{(gnu services)} module also defines several essential
service types, some of which are listed below.

@defvr {Scheme Variable} system-service-type
This is the root of the service graph.  It produces the system directory as
returned by the @command{guix system build} command.
@end defvr

@defvr {Scheme Variable} boot-service-type
The type of the ``boot service'', which produces the @dfn{boot script}.  The
boot script is what the initial RAM disk runs when booting.
@end defvr

@defvr {Scheme Variable} etc-service-type
The type of the @file{/etc} service.  This service is used to create files
under @file{/etc} and can be extended by passing it name/file tuples such
as:

@example
(list `("issue" ,(plain-file "issue" "Welcome!\n")))
@end example

In this example, the effect would be to add an @file{/etc/issue} file
pointing to the given file.
@end defvr

@defvr {Scheme Variable} setuid-program-service-type
Type for the ``setuid-program service''.  This service collects lists of
executable file names, passed as gexps, and adds them to the set of
setuid-root programs on the system (@pxref{Setuid-Programme}).
@end defvr

@defvr {Scheme Variable} profile-service-type
Type of the service that populates the @dfn{system profile}---i.e., the
programs under @file{/run/current-system/profile}.  Other services can
extend it by passing it lists of packages to add to the system profile.
@end defvr


@node Shepherd-Dienste
@subsubsection Shepherd-Dienste

@cindex shepherd services
@cindex PID 1
@cindex init system
The @code{(gnu services shepherd)} module provides a way to define services
managed by the GNU@tie{}Shepherd, which is the GuixSD initialization
system---the first process that is started when the system boots, also known
as PID@tie{}1 (@pxref{Einführung,,, shepherd, The GNU Shepherd Manual}).

Services in the Shepherd can depend on each other.  For instance, the SSH
daemon may need to be started after the syslog daemon has been started,
which in turn can only happen once all the file systems have been mounted.
The simple operating system defined earlier (@pxref{Das Konfigurationssystems nutzen}) results in a service graph like this:

@image{images/shepherd-graph,,5in,Typical shepherd service graph.}

You can actually generate such a graph for any operating system definition
using the @command{guix system shepherd-graph} command
(@pxref{system-shepherd-graph, @command{guix system shepherd-graph}}).

The @var{%shepherd-root-service} is a service object representing
PID@tie{}1, of type @var{shepherd-root-service-type}; it can be extended by
passing it lists of @code{<shepherd-service>} objects.

@deftp {Data Type} shepherd-service
The data type representing a service managed by the Shepherd.

@table @asis
@item @code{provision}
This is a list of symbols denoting what the service provides.

These are the names that may be passed to @command{herd start},
@command{herd status}, and similar commands (@pxref{Invoking herd,,,
shepherd, The GNU Shepherd Manual}).  @xref{Slots of services, the
@code{provides} slot,, shepherd, The GNU Shepherd Manual}, for details.

@item @code{requirements} (default: @code{'()})
List of symbols denoting the Shepherd services this one depends on.

@item @code{respawn?} (default: @code{#t})
Whether to restart the service when it stops, for instance when the
underlying process dies.

@item @code{start}
@itemx @code{stop} (default: @code{#~(const #f)})
The @code{start} and @code{stop} fields refer to the Shepherd's facilities
to start and stop processes (@pxref{Service De- and Constructors,,,
shepherd, The GNU Shepherd Manual}).  They are given as G-expressions that
get expanded in the Shepherd configuration file (@pxref{G-Ausdrücke}).

@item @code{actions} (default: @code{'()})
@cindex actions, of Shepherd services
This is a list of @code{shepherd-action} objects (see below) defining
@dfn{actions} supported by the service, in addition to the standard
@code{start} and @code{stop} actions.  Actions listed here become available
as @command{herd} sub-commands:

@example
herd @var{action} @var{service} [@var{arguments}@dots{}]
@end example

@item @code{Dokumentation}
A documentation string, as shown when running:

@example
herd doc @var{service-name}
@end example

where @var{service-name} is one of the symbols in @var{provision}
(@pxref{Invoking herd,,, shepherd, The GNU Shepherd Manual}).

@item @code{modules} (default: @var{%default-modules})
This is the list of modules that must be in scope when @code{start} and
@code{stop} are evaluated.

@end table
@end deftp

@deftp {Data Type} shepherd-action
This is the data type that defines additional actions implemented by a
Shepherd service (see above).

@table @code
@item name
Symbol naming the action.

@item Dokumentation
This is a documentation string for the action.  It can be viewed by running:

@example
herd doc @var{service} action @var{action}
@end example

@item procedure
This should be a gexp that evaluates to a procedure of at least one
argument, which is the ``running value'' of the service (@pxref{Slots of
services,,, shepherd, The GNU Shepherd Manual}).
@end table

The following example defines an action called @code{say-hello} that kindly
greets the user:

@example
(shepherd-action
  (name 'say-hello)
  (documentation "Say hi!")
  (procedure #~(lambda (running . args)
                 (format #t "Hello, friend! arguments: ~s\n"
                         args)
                 #t)))
@end example

Assuming this action is added to the @code{example} service, then you can
do:

@example
# herd say-hello example
Hello, friend! arguments: ()
# herd say-hello example a b c
Hello, friend! arguments: ("a" "b" "c")
@end example

This, as you can see, is a fairly sophisticated way to say hello.
@xref{Service Convenience,,, shepherd, The GNU Shepherd Manual}, for more
info on actions.
@end deftp

@defvr {Scheme Variable} shepherd-root-service-type
The service type for the Shepherd ``root service''---i.e., PID@tie{}1.

This is the service type that extensions target when they want to create
shepherd services (@pxref{Diensttypen und Dienste}, for an example).
Each extension must pass a list of @code{<shepherd-service>}.
@end defvr

@defvr {Scheme Variable} %shepherd-root-service
This service represents PID@tie{}1.
@end defvr


@node Dokumentation
@section Dokumentation

@cindex documentation, searching for
@cindex searching for documentation
@cindex Info, documentation format
@cindex man pages
@cindex manual pages
In most cases packages installed with Guix come with documentation.  There
are two main documentation formats: ``Info'', a browseable hypertext format
used for GNU software, and ``manual pages'' (or ``man pages''), the linear
documentation format traditionally found on Unix.  Info manuals are accessed
with the @command{info} command or with Emacs, and man pages are accessed
using @command{man}.

You can look for documentation of software installed on your system by
keyword.  For example, the following command searches for information about
``TLS'' in Info manuals:

@example
$ info -k TLS
"(emacs)Network Security" -- STARTTLS
"(emacs)Network Security" -- TLS
"(gnutls)Core TLS API" -- gnutls_certificate_set_verify_flags
"(gnutls)Core TLS API" -- gnutls_certificate_set_verify_function
@dots{}
@end example

@noindent
The command below searches for the same keyword in man pages:

@example
$ man -k TLS
SSL (7)              - OpenSSL SSL/TLS library
certtool (1)         - GnuTLS certificate tool
@dots {}
@end example

These searches are purely local to your computer so you have the guarantee
that documentation you find corresponds to what you have actually installed,
you can access it off-line, and your privacy is respected.

Once you have these results, you can view the relevant documentation by
running, say:

@example
$ info "(gnutls)Core TLS API"
@end example

@noindent
or:

@example
$ man certtool
@end example

Info manuals contain sections and indices as well as hyperlinks like those
found in Web pages.  The @command{info} reader (@pxref{Top, Info reader,,
info-stnd, Stand-alone GNU Info}) and its Emacs counterpart (@pxref{Misc
Help,,, emacs, The GNU Emacs Manual}) provide intuitive key bindings to
navigate manuals.  @xref{Getting Started,,, info, Info: An Introduction},
for an introduction to Info navigation.

@node Dateien zur Fehlersuche installieren
@section Dateien zur Fehlersuche installieren

@cindex debugging files
Program binaries, as produced by the GCC compilers for instance, are
typically written in the ELF format, with a section containing
@dfn{debugging information}.  Debugging information is what allows the
debugger, GDB, to map binary code to source code; it is required to debug a
compiled program in good conditions.

The problem with debugging information is that is takes up a fair amount of
disk space.  For example, debugging information for the GNU C Library weighs
in at more than 60 MiB.  Thus, as a user, keeping all the debugging info of
all the installed programs is usually not an option.  Yet, space savings
should not come at the cost of an impediment to debugging---especially in
the GNU system, which should make it easier for users to exert their
computing freedom (@pxref{GNU-Distribution}).

Thankfully, the GNU Binary Utilities (Binutils) and GDB provide a mechanism
that allows users to get the best of both worlds: debugging information can
be stripped from the binaries and stored in separate files.  GDB is then
able to load debugging information from those files, when they are available
(@pxref{Separate Debug Files,,, gdb, Debugging with GDB}).

The GNU distribution takes advantage of this by storing debugging
information in the @code{lib/debug} sub-directory of a separate package
output unimaginatively called @code{debug} (@pxref{Pakete mit mehreren Ausgaben.}).  Users can choose to install the @code{debug} output of a package
when they need it.  For instance, the following command installs the
debugging information for the GNU C Library and for GNU Guile:

@example
guix package -i glibc:debug guile:debug
@end example

GDB must then be told to look for debug files in the user's profile, by
setting the @code{debug-file-directory} variable (consider setting it from
the @file{~/.gdbinit} file, @pxref{Startup,,, gdb, Debugging with GDB}):

@example
(gdb) set debug-file-directory ~/.guix-profile/lib/debug
@end example

From there on, GDB will pick up debugging information from the @code{.debug}
files under @file{~/.guix-profile/lib/debug}.

In addition, you will most likely want GDB to be able to show the source
code being debugged.  To do that, you will have to unpack the source code of
the package of interest (obtained with @code{guix build --source},
@pxref{Aufruf von guix build}), and to point GDB to that source directory
using the @code{directory} command (@pxref{Source Path, @code{directory},,
gdb, Debugging with GDB}).

@c XXX: keep me up-to-date
The @code{debug} output mechanism in Guix is implemented by the
@code{gnu-build-system} (@pxref{Erstellungssysteme}).  Currently, it is
opt-in---debugging information is available only for the packages with
definitions explicitly declaring a @code{debug} output.  This may be changed
to opt-out in the future if our build farm servers can handle the load.  To
check whether a package has a @code{debug} output, use @command{guix package
--list-available} (@pxref{Aufruf von guix package}).


@node Sicherheitsaktualisierungen
@section Sicherheitsaktualisierungen

@cindex security updates
@cindex security vulnerabilities
Occasionally, important security vulnerabilities are discovered in software
packages and must be patched.  Guix developers try hard to keep track of
known vulnerabilities and to apply fixes as soon as possible in the
@code{master} branch of Guix (we do not yet provide a ``stable'' branch
containing only security updates.)  The @command{guix lint} tool helps
developers find out about vulnerable versions of software packages in the
distribution:

@smallexample
$ guix lint -c cve
gnu/packages/base.scm:652:2: glibc@@2.21: probably vulnerable to CVE-2015-1781, CVE-2015-7547
gnu/packages/gcc.scm:334:2: gcc@@4.9.3: probably vulnerable to CVE-2015-5276
gnu/packages/image.scm:312:2: openjpeg@@2.1.0: probably vulnerable to CVE-2016-1923, CVE-2016-1924
@dots{}
@end smallexample

@xref{Aufruf von guix lint}, for more information.

@quotation Anmerkung
As of version @value{VERSION}, the feature described below is considered
``beta''.
@end quotation

Guix follows a functional package management discipline
(@pxref{Einführung}), which implies that, when a package is changed,
@emph{every package that depends on it} must be rebuilt.  This can
significantly slow down the deployment of fixes in core packages such as
libc or Bash, since basically the whole distribution would need to be
rebuilt.  Using pre-built binaries helps (@pxref{Substitute}), but
deployment may still take more time than desired.

@cindex grafts
To address this, Guix implements @dfn{grafts}, a mechanism that allows for
fast deployment of critical updates without the costs associated with a
whole-distribution rebuild.  The idea is to rebuild only the package that
needs to be patched, and then to ``graft'' it onto packages explicitly
installed by the user and that were previously referring to the original
package.  The cost of grafting is typically very low, and order of
magnitudes lower than a full rebuild of the dependency chain.

@cindex replacements of packages, for grafts
For instance, suppose a security update needs to be applied to Bash.  Guix
developers will provide a package definition for the ``fixed'' Bash, say
@var{bash-fixed}, in the usual way (@pxref{Pakete definieren}).  Then, the
original package definition is augmented with a @code{replacement} field
pointing to the package containing the bug fix:

@example
(define bash
  (package
    (name "bash")
    ;; @dots{}
    (replacement bash-fixed)))
@end example

From there on, any package depending directly or indirectly on Bash---as
reported by @command{guix gc --requisites} (@pxref{Aufruf von guix gc})---that
is installed is automatically ``rewritten'' to refer to @var{bash-fixed}
instead of @var{bash}.  This grafting process takes time proportional to the
size of the package, usually less than a minute for an ``average'' package
on a recent machine.  Grafting is recursive: when an indirect dependency
requires grafting, then grafting ``propagates'' up to the package that the
user is installing.

Currently, the length of the name and version of the graft and that of the
package it replaces (@var{bash-fixed} and @var{bash} in the example above)
must be equal.  This restriction mostly comes from the fact that grafting
works by patching files, including binary files, directly.  Other
restrictions may apply: for instance, when adding a graft to a package
providing a shared library, the original shared library and its replacement
must have the same @code{SONAME} and be binary-compatible.

The @option{--no-grafts} command-line option allows you to forcefully avoid
grafting (@pxref{Gemeinsame Erstellungsoptionen, @option{--no-grafts}}).  Thus, the
command:

@example
guix build bash --no-grafts
@end example

@noindent
returns the store file name of the original Bash, whereas:

@example
guix build bash
@end example

@noindent
returns the store file name of the ``fixed'', replacement Bash.  This allows
you to distinguish between the two variants of Bash.

To verify which Bash your whole profile refers to, you can run
(@pxref{Aufruf von guix gc}):

@example
guix gc -R `readlink -f ~/.guix-profile` | grep bash
@end example

@noindent
@dots{} and compare the store file names that you get with those above.
Likewise for a complete GuixSD system generation:

@example
guix gc -R `guix system build my-config.scm` | grep bash
@end example

Lastly, to check which Bash running processes are using, you can use the
@command{lsof} command:

@example
lsof | grep /gnu/store/.*bash
@end example


@node Paketmodule
@section Paketmodule

From a programming viewpoint, the package definitions of the GNU
distribution are provided by Guile modules in the @code{(gnu packages
@dots{})} name space@footnote{Note that packages under the @code{(gnu
packages @dots{})} module name space are not necessarily ``GNU packages''.
This module naming scheme follows the usual Guile module naming convention:
@code{gnu} means that these modules are distributed as part of the GNU
system, and @code{packages} identifies modules that define packages.}
(@pxref{Module, Guile modules,, guile, GNU Guile Reference Manual}).  For
instance, the @code{(gnu packages emacs)} module exports a variable named
@code{emacs}, which is bound to a @code{<package>} object (@pxref{Pakete definieren}).

The @code{(gnu packages @dots{})} module name space is automatically scanned
for packages by the command-line tools.  For instance, when running
@code{guix package -i emacs}, all the @code{(gnu packages @dots{})} modules
are scanned until one that exports a package object whose name is
@code{emacs} is found.  This package search facility is implemented in the
@code{(gnu packages)} module.

@cindex Anpassung, von Paketen
@cindex package module search path
Users can store package definitions in modules with different names---e.g.,
@code{(my-packages emacs)}@footnote{Note that the file name and module name
must match.  For instance, the @code{(my-packages emacs)} module must be
stored in a @file{my-packages/emacs.scm} file relative to the load path
specified with @option{--load-path} or @code{GUIX_PACKAGE_PATH}.
@xref{Modules and the File System,,, guile, GNU Guile Reference Manual}, for
details.}.  There are two ways to make these package definitions visible to
the user interfaces:

@enumerate
@item
By adding the directory containing your package modules to the search path
with the @code{-L} flag of @command{guix package} and other commands
(@pxref{Gemeinsame Erstellungsoptionen}), or by setting the @code{GUIX_PACKAGE_PATH}
environment variable described below.

@item
By defining a @dfn{channel} and configuring @command{guix pull} so that it
pulls from it.  A channel is essentially a Git repository containing package
modules.  @xref{Channels}, for more information on how to define and use
channels.
@end enumerate

@code{GUIX_PACKAGE_PATH} works similarly to other search path variables:

@defvr {Environment Variable} GUIX_PACKAGE_PATH
This is a colon-separated list of directories to search for additional
package modules.  Directories listed in this variable take precedence over
the own modules of the distribution.
@end defvr

The distribution is fully @dfn{bootstrapped} and @dfn{self-contained}: each
package is built based solely on other packages in the distribution.  The
root of this dependency graph is a small set of @dfn{bootstrap binaries},
provided by the @code{(gnu packages bootstrap)} module.  For more
information on bootstrapping, @pxref{Bootstrapping}.

@node Paketrichtlinien
@section Paketrichtlinien

@cindex packages, creating
The GNU distribution is nascent and may well lack some of your favorite
packages.  This section describes how you can help make the distribution
grow.  @xref{Mitwirken}, for additional information on how you can help.

Free software packages are usually distributed in the form of @dfn{source
code tarballs}---typically @file{tar.gz} files that contain all the source
files.  Adding a package to the distribution means essentially two things:
adding a @dfn{recipe} that describes how to build the package, including a
list of other packages required to build it, and adding @dfn{package
metadata} along with that recipe, such as a description and licensing
information.

In Guix all this information is embodied in @dfn{package definitions}.
Package definitions provide a high-level view of the package.  They are
written using the syntax of the Scheme programming language; in fact, for
each package we define a variable bound to the package definition, and
export that variable from a module (@pxref{Paketmodule}).  However,
in-depth Scheme knowledge is @emph{not} a prerequisite for creating
packages.  For more information on package definitions, @pxref{Pakete definieren}.

Once a package definition is in place, stored in a file in the Guix source
tree, it can be tested using the @command{guix build} command
(@pxref{Aufruf von guix build}).  For example, assuming the new package is
called @code{gnew}, you may run this command from the Guix build tree
(@pxref{Guix vor der Installation ausführen}):

@example
./pre-inst-env guix build gnew --keep-failed
@end example

Using @code{--keep-failed} makes it easier to debug build failures since it
provides access to the failed build tree.  Another useful command-line
option when debugging is @code{--log-file}, to access the build log.

If the package is unknown to the @command{guix} command, it may be that the
source file contains a syntax error, or lacks a @code{define-public} clause
to export the package variable.  To figure it out, you may load the module
from Guile to get more information about the actual error:

@example
./pre-inst-env guile -c '(use-modules (gnu packages gnew))'
@end example

Once your package builds correctly, please send us a patch
(@pxref{Mitwirken}).  Well, if you need help, we will be happy to help
you too.  Once the patch is committed in the Guix repository, the new
package automatically gets built on the supported platforms by
@url{http://hydra.gnu.org/jobset/gnu/master, our continuous integration
system}.

@cindex substituter
Users can obtain the new package definition simply by running @command{guix
pull} (@pxref{Aufruf von guix pull}).  When @code{hydra.gnu.org} is done
building the package, installing the package automatically downloads
binaries from there (@pxref{Substitute}).  The only place where human
intervention is needed is to review and apply the patch.


@menu
* Software-Freiheit::        Was in die Distribution aufgenommen werden 
                               darf.
* Paketbenennung::           Was macht einen Namen aus?
* Versionsnummern::          Wenn der Name noch nicht genug ist.
* Zusammenfassungen und Beschreibungen::  Den Nutzern helfen, das richtige 
                                            Paket zu finden.
* Python-Module::            Ein Touch britischer Comedy.
* Perl-Module::              Kleine Perlen.
* Java-Pakete::              Kaffeepause.
* Schriftarten::             Schriften verschriftlicht.
@end menu

@node Software-Freiheit
@subsection Software-Freiheit

@c Adapted from http://www.gnu.org/philosophy/philosophy.html.
@cindex free software
The GNU operating system has been developed so that users can have freedom
in their computing.  GNU is @dfn{free software}, meaning that users have the
@url{http://www.gnu.org/philosophy/free-sw.html,four essential freedoms}: to
run the program, to study and change the program in source code form, to
redistribute exact copies, and to distribute modified versions.  Packages
found in the GNU distribution provide only software that conveys these four
freedoms.

In addition, the GNU distribution follow the
@url{http://www.gnu.org/distros/free-system-distribution-guidelines.html,free
software distribution guidelines}.  Among other things, these guidelines
reject non-free firmware, recommendations of non-free software, and discuss
ways to deal with trademarks and patents.

Some otherwise free upstream package sources contain a small and optional
subset that violates the above guidelines, for instance because this subset
is itself non-free code.  When that happens, the offending items are removed
with appropriate patches or code snippets in the @code{origin} form of the
package (@pxref{Pakete definieren}).  This way, @code{guix build --source}
returns the ``freed'' source rather than the unmodified upstream source.


@node Paketbenennung
@subsection Paketbenennung

@cindex package name
A package has actually two names associated with it: First, there is the
name of the @emph{Scheme variable}, the one following @code{define-public}.
By this name, the package can be made known in the Scheme code, for instance
as input to another package.  Second, there is the string in the @code{name}
field of a package definition.  This name is used by package management
commands such as @command{guix package} and @command{guix build}.

Both are usually the same and correspond to the lowercase conversion of the
project name chosen upstream, with underscores replaced with hyphens.  For
instance, GNUnet is available as @code{gnunet}, and SDL_net as
@code{sdl-net}.

We do not add @code{lib} prefixes for library packages, unless these are
already part of the official project name.  But @pxref{Python-Module} and
@ref{Perl-Module} for special rules concerning modules for the Python and
Perl languages.

Font package names are handled differently, @pxref{Schriftarten}.


@node Versionsnummern
@subsection Versionsnummern

@cindex package version
We usually package only the latest version of a given free software
project.  But sometimes, for instance for incompatible library versions, two
(or more) versions of the same package are needed.  These require different
Scheme variable names.  We use the name as defined in @ref{Paketbenennung}
for the most recent version; previous versions use the same name, suffixed
by @code{-} and the smallest prefix of the version number that may
distinguish the two versions.

The name inside the package definition is the same for all versions of a
package and does not contain any version number.

For instance, the versions 2.24.20 and 3.9.12 of GTK+ may be packaged as
follows:

@example
(define-public gtk+
  (package
    (name "gtk+")
    (version "3.9.12")
    ...))
(define-public gtk+-2
  (package
    (name "gtk+")
    (version "2.24.20")
    ...))
@end example
If we also wanted GTK+ 3.8.2, this would be packaged as
@example
(define-public gtk+-3.8
  (package
    (name "gtk+")
    (version "3.8.2")
    ...))
@end example

@c See <https://lists.gnu.org/archive/html/guix-devel/2016-01/msg00425.html>,
@c for a discussion of what follows.
@cindex version number, for VCS snapshots
Occasionally, we package snapshots of upstream's version control system
(VCS) instead of formal releases.  This should remain exceptional, because
it is up to upstream developers to clarify what the stable release is.  Yet,
it is sometimes necessary.  So, what should we put in the @code{version}
field?

Clearly, we need to make the commit identifier of the VCS snapshot visible
in the version string, but we also need to make sure that the version string
is monotonically increasing so that @command{guix package --upgrade} can
determine which version is newer.  Since commit identifiers, notably with
Git, are not monotonically increasing, we add a revision number that we
increase each time we upgrade to a newer snapshot.  The resulting version
string looks like this:

@example
2.0.11-3.cabba9e
  ^    ^    ^
  |    |    `-- upstream commit ID
  |    |
  |    `--- Guix package revision
  |
latest upstream version
@end example

It is a good idea to strip commit identifiers in the @code{version} field
to, say, 7 digits.  It avoids an aesthetic annoyance (assuming aesthetics
have a role to play here) as well as problems related to OS limits such as
the maximum shebang length (127 bytes for the Linux kernel.)  It is best to
use the full commit identifiers in @code{origin}s, though, to avoid
ambiguities.  A typical package definition may look like this:

@example
(define my-package
  (let ((commit "c3f29bc928d5900971f65965feaae59e1272a3f7")
        (revision "1"))          ;Guix package revision
    (package
      (version (git-version "0.9" revision commit))
      (source (origin
                (method git-fetch)
                (uri (git-reference
                      (url "git://example.org/my-package.git")
                      (commit commit)))
                (sha256 (base32 "1mbikn@dots{}"))
                (file-name (git-file-name name version))))
      ;; @dots{}
      )))
@end example

@node Zusammenfassungen und Beschreibungen
@subsection Zusammenfassungen und Beschreibungen

@cindex package description
@cindex package synopsis
As we have seen before, each package in GNU@tie{}Guix includes a synopsis
and a description (@pxref{Pakete definieren}).  Synopses and descriptions
are important: They are what @command{guix package --search} searches, and a
crucial piece of information to help users determine whether a given package
suits their needs.  Consequently, packagers should pay attention to what
goes into them.

Synopses must start with a capital letter and must not end with a period.
They must not start with ``a'' or ``the'', which usually does not bring
anything; for instance, prefer ``File-frobbing tool'' over ``A tool that
frobs files''.  The synopsis should say what the package is---e.g., ``Core
GNU utilities (file, text, shell)''---or what it is used for---e.g., the
synopsis for GNU@tie{}grep is ``Print lines matching a pattern''.

Keep in mind that the synopsis must be meaningful for a very wide audience.
For example, ``Manipulate alignments in the SAM format'' might make sense
for a seasoned bioinformatics researcher, but might be fairly unhelpful or
even misleading to a non-specialized audience.  It is a good idea to come up
with a synopsis that gives an idea of the application domain of the
package.  In this example, this might give something like ``Manipulate
nucleotide sequence alignments'', which hopefully gives the user a better
idea of whether this is what they are looking for.

Descriptions should take between five and ten lines.  Use full sentences,
and avoid using acronyms without first introducing them.  Please avoid
marketing phrases such as ``world-leading'', ``industrial-strength'', and
``next-generation'', and avoid superlatives like ``the most
advanced''---they are not helpful to users looking for a package and may
even sound suspicious.  Instead, try to be factual, mentioning use cases and
features.

@cindex Texinfo markup, in package descriptions
Descriptions can include Texinfo markup, which is useful to introduce
ornaments such as @code{@@code} or @code{@@dfn}, bullet lists, or hyperlinks
(@pxref{Overview,,, texinfo, GNU Texinfo}).  However you should be careful
when using some characters for example @samp{@@} and curly braces which are
the basic special characters in Texinfo (@pxref{Special Characters,,,
texinfo, GNU Texinfo}).  User interfaces such as @command{guix package
--show} take care of rendering it appropriately.

Synopses and descriptions are translated by volunteers
@uref{http://translationproject.org/domain/guix-packages.html, at the
Translation Project} so that as many users as possible can read them in
their native language.  User interfaces search them and display them in the
language specified by the current locale.

To allow @command{xgettext} to extract them as translatable strings,
synopses and descriptions @emph{must be literal strings}.  This means that
you cannot use @code{string-append} or @code{format} to construct these
strings:

@lisp
(package
  ;; @dots{}
  (synopsis "This is translatable")
  (description (string-append "This is " "*not*" " translatable.")))
@end lisp

Translation is a lot of work so, as a packager, please pay even more
attention to your synopses and descriptions as every change may entail
additional work for translators.  In order to help them, it is possible to
make recommendations or instructions visible to them by inserting special
comments like this (@pxref{xgettext Invocation,,, gettext, GNU Gettext}):

@example
;; TRANSLATORS: "X11 resize-and-rotate" should not be translated.
(description "ARandR is designed to provide a simple visual front end
for the X11 resize-and-rotate (RandR) extension. @dots{}")
@end example


@node Python-Module
@subsection Python-Module

@cindex python
We currently package Python 2 and Python 3, under the Scheme variable names
@code{python-2} and @code{python} as explained in @ref{Versionsnummern}.  To
avoid confusion and naming clashes with other programming languages, it
seems desirable that the name of a package for a Python module contains the
word @code{python}.

Some modules are compatible with only one version of Python, others with
both.  If the package Foo compiles only with Python 3, we name it
@code{python-foo}; if it compiles only with Python 2, we name it
@code{python2-foo}. If it is compatible with both versions, we create two
packages with the corresponding names.

If a project already contains the word @code{python}, we drop this; for
instance, the module python-dateutil is packaged under the names
@code{python-dateutil} and @code{python2-dateutil}.  If the project name
starts with @code{py} (e.g. @code{pytz}), we keep it and prefix it as
described above.

@subsubsection Specifying Dependencies
@cindex inputs, for Python packages

Dependency information for Python packages is usually available in the
package source tree, with varying degrees of accuracy: in the
@file{setup.py} file, in @file{requirements.txt}, or in @file{tox.ini}.

Your mission, when writing a recipe for a Python package, is to map these
dependencies to the appropriate type of ``input'' (@pxref{„package“-Referenz,
inputs}).  Although the @code{pypi} importer normally does a good job
(@pxref{Aufruf von guix import}), you may want to check the following check
list to determine which dependency goes where.

@itemize

@item
We currently package Python 2 with @code{setuptools} and @code{pip}
installed like Python 3.4 has per default.  Thus you don't need to specify
either of these as an input.  @command{guix lint} will warn you if you do.

@item
Python dependencies required at run time go into @code{propagated-inputs}.
They are typically defined with the @code{install_requires} keyword in
@file{setup.py}, or in the @file{requirements.txt} file.

@item
Python packages required only at build time---e.g., those listed with the
@code{setup_requires} keyword in @file{setup.py}---or only for
testing---e.g., those in @code{tests_require}---go into
@code{native-inputs}.  The rationale is that (1) they do not need to be
propagated because they are not needed at run time, and (2) in a
cross-compilation context, it's the ``native'' input that we'd want.

Examples are the @code{pytest}, @code{mock}, and @code{nose} test
frameworks.  Of course if any of these packages is also required at
run-time, it needs to go to @code{propagated-inputs}.

@item
Anything that does not fall in the previous categories goes to
@code{inputs}, for example programs or C libraries required for building
Python packages containing C extensions.

@item
If a Python package has optional dependencies (@code{extras_require}), it is
up to you to decide whether to add them or not, based on their
usefulness/overhead ratio (@pxref{Einreichen von Patches, @command{guix size}}).

@end itemize


@node Perl-Module
@subsection Perl-Module

@cindex perl
Perl programs standing for themselves are named as any other package, using
the lowercase upstream name.  For Perl packages containing a single class,
we use the lowercase class name, replace all occurrences of @code{::} by
dashes and prepend the prefix @code{perl-}.  So the class @code{XML::Parser}
becomes @code{perl-xml-parser}.  Modules containing several classes keep
their lowercase upstream name and are also prepended by @code{perl-}.  Such
modules tend to have the word @code{perl} somewhere in their name, which
gets dropped in favor of the prefix.  For instance, @code{libwww-perl}
becomes @code{perl-libwww}.


@node Java-Pakete
@subsection Java-Pakete

@cindex java
Java programs standing for themselves are named as any other package, using
the lowercase upstream name.

To avoid confusion and naming clashes with other programming languages, it
is desirable that the name of a package for a Java package is prefixed with
@code{java-}.  If a project already contains the word @code{java}, we drop
this; for instance, the package @code{ngsjava} is packaged under the name
@code{java-ngs}.

For Java packages containing a single class or a small class hierarchy, we
use the lowercase class name, replace all occurrences of @code{.} by dashes
and prepend the prefix @code{java-}.  So the class @code{apache.commons.cli}
becomes package @code{java-apache-commons-cli}.


@node Schriftarten
@subsection Schriftarten

@cindex Schriftarten
For fonts that are in general not installed by a user for typesetting
purposes, or that are distributed as part of a larger software package, we
rely on the general packaging rules for software; for instance, this applies
to the fonts delivered as part of the X.Org system or fonts that are part of
TeX Live.

To make it easier for a user to search for fonts, names for other packages
containing only fonts are constructed as follows, independently of the
upstream package name.

The name of a package containing only one font family starts with
@code{font-}; it is followed by the foundry name and a dash @code{-} if the
foundry is known, and the font family name, in which spaces are replaced by
dashes (and as usual, all upper case letters are transformed to lower
case).  For example, the Gentium font family by SIL is packaged under the
name @code{font-sil-gentium}.

For a package containing several font families, the name of the collection
is used in the place of the font family name.  For instance, the Liberation
fonts consist of three families, Liberation Sans, Liberation Serif and
Liberation Mono.  These could be packaged separately under the names
@code{font-liberation-sans} and so on; but as they are distributed together
under a common name, we prefer to package them together as
@code{font-liberation}.

In the case where several formats of the same font family or font collection
are packaged separately, a short form of the format, prepended by a dash, is
added to the package name.  We use @code{-ttf} for TrueType fonts,
@code{-otf} for OpenType fonts and @code{-type1} for PostScript Type 1
fonts.



@node Bootstrapping
@section Bootstrapping

@c Adapted from the ELS 2013 paper.

@cindex bootstrapping

Bootstrapping in our context refers to how the distribution gets built
``from nothing''.  Remember that the build environment of a derivation
contains nothing but its declared inputs (@pxref{Einführung}).  So there's
an obvious chicken-and-egg problem: how does the first package get built?
How does the first compiler get compiled? Note that this is a question of
interest only to the curious hacker, not to the regular user, so you can
shamelessly skip this section if you consider yourself a ``regular user''.

@cindex bootstrap binaries
The GNU system is primarily made of C code, with libc at its core.  The GNU
build system itself assumes the availability of a Bourne shell and
command-line tools provided by GNU Coreutils, Awk, Findutils, `sed', and
`grep'.  Furthermore, build programs---programs that run @code{./configure},
@code{make}, etc.---are written in Guile Scheme (@pxref{Ableitungen}).
Consequently, to be able to build anything at all, from scratch, Guix relies
on pre-built binaries of Guile, GCC, Binutils, libc, and the other packages
mentioned above---the @dfn{bootstrap binaries}.

These bootstrap binaries are ``taken for granted'', though we can also
re-create them if needed (more on that later).

@unnumberedsubsec Preparing to Use the Bootstrap Binaries

@c As of Emacs 24.3, Info-mode displays the image, but since it's a
@c large image, it's hard to scroll.  Oh well.
@image{images/bootstrap-graph,6in,,Dependency graph of the early bootstrap
derivations}

The figure above shows the very beginning of the dependency graph of the
distribution, corresponding to the package definitions of the @code{(gnu
packages bootstrap)} module.  A similar figure can be generated with
@command{guix graph} (@pxref{Aufruf von guix graph}), along the lines of:

@example
guix graph -t derivation \
  -e '(@@@@ (gnu packages bootstrap) %bootstrap-gcc)' \
  | dot -Tps > t.ps
@end example

At this level of detail, things are slightly complex.  First, Guile itself
consists of an ELF executable, along with many source and compiled Scheme
files that are dynamically loaded when it runs.  This gets stored in the
@file{guile-2.0.7.tar.xz} tarball shown in this graph.  This tarball is part
of Guix's ``source'' distribution, and gets inserted into the store with
@code{add-to-store} (@pxref{Der Store}).

But how do we write a derivation that unpacks this tarball and adds it to
the store? To solve this problem, the @code{guile-bootstrap-2.0.drv}
derivation---the first one that gets built---uses @code{bash} as its
builder, which runs @code{build-bootstrap-guile.sh}, which in turn calls
@code{tar} to unpack the tarball.  Thus, @file{bash}, @file{tar}, @file{xz},
and @file{mkdir} are statically-linked binaries, also part of the Guix
source distribution, whose sole purpose is to allow the Guile tarball to be
unpacked.

Once @code{guile-bootstrap-2.0.drv} is built, we have a functioning Guile
that can be used to run subsequent build programs.  Its first task is to
download tarballs containing the other pre-built binaries---this is what the
@code{.tar.xz.drv} derivations do.  Guix modules such as
@code{ftp-client.scm} are used for this purpose.  The
@code{module-import.drv} derivations import those modules in a directory in
the store, using the original layout.  The @code{module-import-compiled.drv}
derivations compile those modules, and write them in an output directory
with the right layout.  This corresponds to the @code{#:modules} argument of
@code{build-expression->derivation} (@pxref{Ableitungen}).

Finally, the various tarballs are unpacked by the derivations
@code{gcc-bootstrap-0.drv}, @code{glibc-bootstrap-0.drv}, etc., at which
point we have a working C tool chain.


@unnumberedsubsec Building the Build Tools

Bootstrapping is complete when we have a full tool chain that does not
depend on the pre-built bootstrap tools discussed above.  This no-dependency
requirement is verified by checking whether the files of the final tool
chain contain references to the @file{/gnu/store} directories of the
bootstrap inputs.  The process that leads to this ``final'' tool chain is
described by the package definitions found in the @code{(gnu packages
commencement)} module.

The @command{guix graph} command allows us to ``zoom out'' compared to the
graph above, by looking at the level of package objects instead of
individual derivations---remember that a package may translate to several
derivations, typically one derivation to download its source, one to build
the Guile modules it needs, and one to actually build the package from
source.  The command:

@example
guix graph -t bag \
  -e '(@@@@ (gnu packages commencement)
          glibc-final-with-bootstrap-bash)' | dot -Tps > t.ps
@end example

@noindent
produces the dependency graph leading to the ``final'' C
library@footnote{You may notice the @code{glibc-intermediate} label,
suggesting that it is not @emph{quite} final, but as a good approximation,
we will consider it final.}, depicted below.

@image{images/bootstrap-packages,6in,,Dependency graph of the early
packages}

@c See <http://lists.gnu.org/archive/html/gnu-system-discuss/2012-10/msg00000.html>.
The first tool that gets built with the bootstrap binaries is
GNU@tie{}Make---noted @code{make-boot0} above---which is a prerequisite for
all the following packages.  From there Findutils and Diffutils get built.

Then come the first-stage Binutils and GCC, built as pseudo cross
tools---i.e., with @code{--target} equal to @code{--host}.  They are used to
build libc.  Thanks to this cross-build trick, this libc is guaranteed not
to hold any reference to the initial tool chain.

From there the final Binutils and GCC (not shown above) are built.  GCC uses
@code{ld} from the final Binutils, and links programs against the just-built
libc.  This tool chain is used to build the other packages used by Guix and
by the GNU Build System: Guile, Bash, Coreutils, etc.

And voilà! At this point we have the complete set of build tools that the
GNU Build System expects.  These are in the @code{%final-inputs} variable of
the @code{(gnu packages commencement)} module, and are implicitly used by
any package that uses @code{gnu-build-system} (@pxref{Erstellungssysteme,
@code{gnu-build-system}}).


@unnumberedsubsec Building the Bootstrap Binaries

@cindex bootstrap binaries
Because the final tool chain does not depend on the bootstrap binaries,
those rarely need to be updated.  Nevertheless, it is useful to have an
automated way to produce them, should an update occur, and this is what the
@code{(gnu packages make-bootstrap)} module provides.

The following command builds the tarballs containing the bootstrap binaries
(Guile, Binutils, GCC, libc, and a tarball containing a mixture of Coreutils
and other basic command-line tools):

@example
guix build bootstrap-tarballs
@end example

The generated tarballs are those that should be referred to in the
@code{(gnu packages bootstrap)} module mentioned at the beginning of this
section.

Still here? Then perhaps by now you've started to wonder: when do we reach a
fixed point? That is an interesting question! The answer is unknown, but if
you would like to investigate further (and have significant computational
and storage resources to do so), then let us know.

@unnumberedsubsec Reducing the Set of Bootstrap Binaries

Our bootstrap binaries currently include GCC, Guile, etc.  That's a lot of
binary code! Why is that a problem? It's a problem because these big chunks
of binary code are practically non-auditable, which makes it hard to
establish what source code produced them.  Every unauditable binary also
leaves us vulnerable to compiler backdoors as described by Ken Thompson in
the 1984 paper @emph{Reflections on Trusting Trust}.

This is mitigated by the fact that our bootstrap binaries were generated
from an earlier Guix revision.  Nevertheless it lacks the level of
transparency that we get in the rest of the package dependency graph, where
Guix always gives us a source-to-binary mapping.  Thus, our goal is to
reduce the set of bootstrap binaries to the bare minimum.

The @uref{http://bootstrappable.org, Bootstrappable.org web site} lists
on-going projects to do that.  One of these is about replacing the bootstrap
GCC with a sequence of assemblers, interpreters, and compilers of increasing
complexity, which could be built from source starting from a simple and
auditable assembler.  Your help is welcome!


@node Portierung
@section Porting to a New Platform

As discussed above, the GNU distribution is self-contained, and
self-containment is achieved by relying on pre-built ``bootstrap binaries''
(@pxref{Bootstrapping}).  These binaries are specific to an operating system
kernel, CPU architecture, and application binary interface (ABI).  Thus, to
port the distribution to a platform that is not yet supported, one must
build those bootstrap binaries, and update the @code{(gnu packages
bootstrap)} module to use them on that platform.

Fortunately, Guix can @emph{cross compile} those bootstrap binaries.  When
everything goes well, and assuming the GNU tool chain supports the target
platform, this can be as simple as running a command like this one:

@example
guix build --target=armv5tel-linux-gnueabi bootstrap-tarballs
@end example

For this to work, the @code{glibc-dynamic-linker} procedure in @code{(gnu
packages bootstrap)} must be augmented to return the right file name for
libc's dynamic linker on that platform; likewise,
@code{system->linux-architecture} in @code{(gnu packages linux)} must be
taught about the new platform.

Once these are built, the @code{(gnu packages bootstrap)} module needs to be
updated to refer to these binaries on the target platform.  That is, the
hashes and URLs of the bootstrap tarballs for the new platform must be added
alongside those of the currently supported platforms.  The bootstrap Guile
tarball is treated specially: it is expected to be available locally, and
@file{gnu/local.mk} has rules do download it for the supported
architectures; a rule for the new platform must be added as well.

In practice, there may be some complications.  First, it may be that the
extended GNU triplet that specifies an ABI (like the @code{eabi} suffix
above) is not recognized by all the GNU tools.  Typically, glibc recognizes
some of these, whereas GCC uses an extra @code{--with-abi} configure flag
(see @code{gcc.scm} for examples of how to handle this).  Second, some of
the required packages could fail to build for that platform.  Lastly, the
generated binaries could be broken for some reason.

@c *********************************************************************
@include contributing.de.texi

@c *********************************************************************
@node Danksagungen
@chapter Danksagungen

Guix is based on the @uref{http://nixos.org/nix/, Nix package manager},
which was designed and implemented by Eelco Dolstra, with contributions from
other people (see the @file{nix/AUTHORS} file in Guix.)  Nix pioneered
functional package management, and promoted unprecedented features, such as
transactional package upgrades and rollbacks, per-user profiles, and
referentially transparent build processes.  Without this work, Guix would
not exist.

The Nix-based software distributions, Nixpkgs and NixOS, have also been an
inspiration for Guix.

GNU@tie{}Guix itself is a collective work with contributions from a number
of people.  See the @file{AUTHORS} file in Guix for more information on
these fine people.  The @file{THANKS} file lists people who have helped by
reporting bugs, taking care of the infrastructure, providing artwork and
themes, making suggestions, and more---thank you!


@c *********************************************************************
@node GNU-Lizenz für freie Dokumentation
@appendix GNU-Lizenz für freie Dokumentation
@cindex license, GNU Free Documentation License
@include fdl-1.3.texi

@c *********************************************************************
@node Konzeptverzeichnis
@unnumbered Konzeptverzeichnis
@printindex cp

@node Programmierverzeichnis
@unnumbered Programmierverzeichnis
@syncodeindex tp fn
@syncodeindex vr fn
@printindex fn

@bye

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