\input texinfo @c -*-texinfo-*- @c %**start of header @setfilename guix.info @documentencoding UTF-8 @settitle GNU Guix Reference Manual @c %**end of header @include version.texi @set YEARS 2012, 2013 @dircategory Package management @direntry * guix: (guix). Guix, the functional package manager. * guix package: (guix)Invoking guix package Managing packages with Guix. * guix build: (guix)Invoking guix build Building packages with Guix. @end direntry @titlepage @title GNU Guix Reference Manual @subtitle Using the GNU Guix Functional Package Manager @author Ludovic Courtès @author Nikita Karetnikov @page @vskip 0pt plus 1filll Edition @value{EDITION} @* @value{UPDATED} @* Copyright @copyright{} @value{YEARS} Ludovic Court@`es @quotation Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. @end quotation @end titlepage @copying This manual documents GNU Guix version @value{VERSION}. Copyright @copyright{} @value{YEARS} Ludovic Courtès Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License.'' @end copying @contents @c ********************************************************************* @node Top @top GNU Guix This document describes GNU Guix version @value{VERSION}, a functional package management tool written for the GNU system. @quotation Copyright @copyright{} @value{YEARS} Ludovic Courtès Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License.'' @end quotation @menu * Introduction:: What is Guix about? * Installation:: Installing Guix. * Package Management:: Package installation, upgrade, etc. * Programming Interface:: Using Guix in Scheme. * Utilities:: Package management commands. * GNU Distribution:: Software for your friendly GNU system. * Contributing:: Your help needed! * Acknowledgments:: Thanks! * GNU Free Documentation License:: The license of this manual. * Concept Index:: Concepts. * Function Index:: Functions. @end menu @c ********************************************************************* @node Introduction @chapter Introduction GNU Guix@footnote{``Guix'' is pronounced like ``geeks'', or ``ɡiːks'' using the international phonetic alphabet (IPA).} is a functional package management tool for the GNU system. Package management consists of all activities that relate to building packages from sources, honoring their build-time and run-time dependencies, installing packages in user environments, upgrading installed packages to new versions or rolling back to a previous set, removing unused software packages, etc. @cindex functional package management The term @dfn{functional} refers to a specific package management discipline. In Guix, the package build and installation process is seen as a function, in the mathematical sense. That function takes inputs, such as build scripts, a compiler, and libraries, and returns an installed package. As a pure function, its result depends solely on its inputs---for instance, it cannot refer to software or scripts that were not explicitly passed as inputs. A build function always produces the same result when passed a given set of inputs. It cannot alter the system's environment in any way; for instance, it cannot create, modify, or delete files outside of its build and installation directories. This is achieved by running build processes in isolated environments (or @dfn{chroots}), where only their explicit inputs are visible. @cindex store The result of package build functions is @dfn{cached} in the file system, in a special directory called @dfn{the store} (@pxref{The Store}). Each package is installed in a directory of its own, in the store---by default under @file{/nix/store}. The directory name contains a hash of all the inputs used to build that package; thus, changing an input yields a different directory name. This approach is the foundation of Guix's salient features: support for transactional package upgrade and rollback, per-user installation, and garbage collection of packages (@pxref{Features}). Guix has a command-line interface, which allows users to build, install, upgrade, and remove packages, as well as a Scheme programming interface. Last but not least, Guix is used to build a distribution of the GNU system, with many GNU and non-GNU free software packages. @xref{GNU Distribution}. @c ********************************************************************* @node Installation @chapter Installation GNU Guix is available for download from its website at @url{http://www.gnu.org/software/guix/}. This section describes the software requirements of Guix, as well as how to install it and get ready to use it. The build procedure for Guix is the same as for other GNU software, and is not covered here. Please see the files @file{README} and @file{INSTALL} in the Guix source tree for additional details. @menu * Requirements:: Software needed to build and run Guix. * Setting Up the Daemon:: Preparing the build daemon's environment. * Invoking guix-daemon:: Running the build daemon. @end menu @node Requirements @section Requirements GNU Guix depends on the following packages: @itemize @item @url{http://gnu.org/software/guile/, GNU Guile}, version 2.0.5 or later; @item @url{http://gnupg.org/, GNU libgcrypt} @end itemize Unless @code{--disable-daemon} was passed to @command{configure}, the following packages are also needed: @itemize @item @url{http://sqlite.org, SQLite 3} @item @url{http://www.bzip.org, libbz2} @item @url{http://gcc.gnu.org, GCC's g++} @end itemize When a working installation of @url{http://nixos.org/nix/, the Nix package manager} is available, you can instead configure Guix with @code{--disable-daemon}. In that case, Nix replaces the three dependencies above. Guix is compatible with Nix, so it is possible to share the same store between both. To do so, you must pass @command{configure} not only the same @code{--with-store-dir} value, but also the same @code{--localstatedir} value. The latter is essential because it specifies where the database that stores metadata about the store is located, among other things. The default values are @code{--with-store-dir=/nix/store} and @code{--localstatedir=/nix/var}. Note that @code{--disable-daemon} is not required if your goal is to share the store with Nix. @node Setting Up the Daemon @section Setting Up the Daemon @cindex daemon Operations such as building a package or running the garbage collector are all performed by a specialized process, the @dfn{Guix daemon}, on behalf of clients. Only the daemon may access the store and its associated database. Thus, any operation that manipulates the store goes through the daemon. For instance, command-line tools such as @command{guix package} and @command{guix build} communicate with the daemon (@i{via} remote procedure calls) to instruct it what to do. In a standard multi-user setup, Guix and its daemon---the @command{guix-daemon} program---are installed by the system administrator; @file{/nix/store} is owned by @code{root} and @command{guix-daemon} runs as @code{root}. Unprivileged users may use Guix tools to build packages or otherwise access the store, and the daemon will do it on their behalf, ensuring that the store is kept in a consistent state, and allowing built packages to be shared among users. @cindex build users When @command{guix-daemon} runs as @code{root}, you may not want package build processes themselves to run as @code{root} too, for obvious security reasons. To avoid that, a special pool of @dfn{build users} should be created for use by build processes started by the daemon. These build users need not have a shell and a home directory: they will just be used when the daemon drops @code{root} privileges in build processes. Having several such users allows the daemon to launch distinct build processes under separate UIDs, which guarantees that they do not interfere with each other---an essential feature since builds are regarded as pure functions (@pxref{Introduction}). On a GNU/Linux system, a build user pool may be created like this (using Bash syntax and the @code{shadow} commands): @c See http://lists.gnu.org/archive/html/bug-guix/2013-01/msg00239.html @c for why `-G' is needed. @example # groupadd guix-builder # for i in `seq 1 10`; do useradd -g guix-builder -G guix-builder \ -d /var/empty -s `which nologin` \ -c "Guix build user $i" guix-builder$i; done @end example @noindent The @code{guix-daemon} program may then be run as @code{root} with: @example # guix-daemon --build-users-group=guix-builder @end example Guix may also be used in a single-user setup, with @command{guix-daemon} running as an unprivileged user. However, to maximize non-interference of build processes, the daemon still needs to perform certain operations that are restricted to @code{root} on GNU/Linux: it should be able to run build processes in a chroot, and to run them under different UIDs. To that end, the @command{nix-setuid-helper} program is provided; it is a small C program (less than 300 lines) that, if it is made setuid @code{root}, can be executed by the daemon to perform these operations on its behalf. The @code{root}-owned @file{/etc/nix-setuid.conf} file is read by @command{nix-setuid-helper}; it should contain exactly two words: the user name under which the authorized @command{guix-daemon} runs, and the name of the build users group. If you are installing Guix as an unprivileged user and do not have the ability to make @file{nix-setuid-helper} setuid-@code{root}, it is still possible to run @command{guix-daemon}. However, build processes will not be isolated from one another, and not from the rest of the system. Thus, build processes may interfere with each other, and may access programs, libraries, and other files available on the system---making it much harder to view them as @emph{pure} functions. @node Invoking guix-daemon @section Invoking @command{guix-daemon} The @command{guix-daemon} program implements all the functionality to access the store. This includes launching build processes, running the garbage collector, querying the availability of a build result, etc. It is normally run as @code{root} like this: @example # guix-daemon --build-users-group=guix-builder @end example @noindent For details on how to set it up, @ref{Setting Up the Daemon}. By default, @command{guix-daemon} launches build processes under different UIDs, taken from the build group specified with @code{--build-users-group}. In addition, each build process is run in a chroot environment that only contains the subset of the store that the build process depends on, as specified by its derivation (@pxref{Programming Interface, derivation}), plus a set of specific system directories. By default, the latter contains @file{/dev} and @file{/dev/pts}. The following command-line options are supported: @table @code @item --build-users-group=@var{group} Take users from @var{group} to run build processes (@pxref{Setting Up the Daemon, build users}). @item --no-substitutes Do not use substitutes for build products. That is, always build things locally instead of allowing downloads of pre-built binaries. @item --cache-failures Cache build failures. By default, only successful builds are cached. @item --cores=@var{n} @itemx -c @var{n} Use @var{n} CPU cores to build each derivation; @code{0} means as many as available. The default value is @code{1}, but it may be overridden by clients, such as the @code{--cores} option of @command{guix build} (@pxref{Invoking guix build}). The effect is to define the @code{NIX_BUILD_CORES} environment variable in the build process, which can then use it to exploit internal parallelism---for instance, by running @code{make -j$NIX_BUILD_CORES}. @item --max-jobs=@var{n} @itemx -M @var{n} Allow at most @var{n} build jobs in parallel. The default value is @code{1}. @item --debug Produce debugging output. This is useful to debug daemon start-up issues, but then it may be overridden by clients, for example the @code{--verbosity} option of @command{guix build} (@pxref{Invoking guix build}). @item --chroot-directory=@var{dir} Add @var{dir} to the build chroot. Doing this may change the result of build processes---for instance if they use optional dependencies found in @var{dir} when it is available, and not otherwise. For that reason, it is not recommended to do so. Instead, make sure that each derivation declares all the inputs that it needs. @item --disable-chroot Disable chroot builds. Using this option is not recommended since, again, it would allow build processes to gain access to undeclared dependencies. @item --disable-log-compression Disable compression of the build logs. Unless @code{--lose-logs} is used, all the build logs are kept in the @var{localstatedir}. To save space, the daemon automatically compresses them with bzip2 by default. This option disables that. @item --disable-store-optimization Disable automatic file ``deduplication'' in the store. By default, files added to the store are automatically ``deduplicated'': if a newly added file is identical as another one found in the store, the daemon makes the new file a hard link to the other file. This slightly increases the input/output load at the end of a build process. This option disables this. @item --impersonate-linux-2.6 On Linux-based systems, impersonate Linux 2.6. This means that the kernel's @code{uname} system call will report 2.6 as the release number. This might be helpful to build programs that (usually wrongfully) depend on the kernel version number. @item --lose-logs Do not keep build logs. By default they are kept under @code{@var{localstatedir}/nix/log}. @item --system=@var{system} Assume @var{system} as the current system type. By default it is the architecture/kernel pair found at configure time, such as @code{x86_64-linux}. @item --listen=@var{socket} Listen for connections on @var{socket}, the file name of a Unix-domain socket. The default socket is @file{@var{localstatedir}/daemon-socket/socket}. This option is only useful in exceptional circumstances, such as if you need to run several daemons on the same machine. @end table @c ********************************************************************* @node Package Management @chapter Package Management The purpose of GNU Guix is to allow users to easily install, upgrade, and remove software packages, without having to know about their build procedure or dependencies. Guix also goes beyond this obvious set of features. This chapter describes the main features of Guix, as well as the package management tools it provides. @menu * Features:: How Guix will make your life brighter. * Invoking guix package:: Package installation, removal, etc. * Packages with Multiple Outputs:: Single source package, multiple outputs. * Invoking guix gc:: Running the garbage collector. * Invoking guix pull:: Fetching the latest Guix and distribution. @end menu @node Features @section Features When using Guix, each package ends up in the @dfn{package store}, in its own directory---something that resembles @file{/nix/store/xxx-package-1.2}, where @code{xxx} is a base32 string. Instead of referring to these directories, users have their own @dfn{profile}, which points to the packages that they actually want to use. These profiles are stored within each user's home directory, at @code{$HOME/.guix-profile}. For example, @code{alice} installs GCC 4.7.2. As a result, @file{/home/alice/.guix-profile/bin/gcc} points to @file{/nix/store/@dots{}-gcc-4.7.2/bin/gcc}. Now, on the same machine, @code{bob} had already installed GCC 4.8.0. The profile of @code{bob} simply continues to point to @file{/nix/store/@dots{}-gcc-4.8.0/bin/gcc}---i.e., both versions of GCC coexist on the same system without any interference. The @command{guix package} command is the central tool to manage packages (@pxref{Invoking guix package}). It operates on those per-user profiles, and can be used @emph{with normal user privileges}. The command provides the obvious install, remove, and upgrade operations. Each invocation is actually a @emph{transaction}: either the specified operation succeeds, or nothing happens. Thus, if the @command{guix package} process is terminated during the transaction, or if a power outage occurs during the transaction, then the user's profile remains in its previous state, and remains usable. In addition, any package transaction may be @emph{rolled back}. So, if, for example, an upgrade installs a new version of a package that turns out to have a serious bug, users may roll back to the previous instance of their profile, which was known to work well. All those packages in the package store may be @emph{garbage-collected}. Guix can determine which packages are still referenced by the user profiles, and remove those that are provably no longer referenced (@pxref{Invoking guix gc}). Users may also explicitly remove old generations of their profile so that the packages they refer to can be collected. Finally, Guix takes a @dfn{purely functional} approach to package management, as described in the introduction (@pxref{Introduction}). Each @file{/nix/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, and helps maximize @dfn{reproducibility}. This foundation allows Guix to support @dfn{transparent binary/source deployment}. When a pre-built binary for a @file{/nix/store} path is available from an external source, Guix just downloads it; otherwise, it builds the package from source, locally. @node Invoking guix package @section Invoking @command{guix package} The @command{guix package} command is the tool that allows users to install, upgrade, and remove packages, as well as rolling back to previous configurations. It operates only on the user's own profile, and works with normal user privileges (@pxref{Features}). Its syntax is: @example guix package @var{options} @end example Primarily, @var{options} specifies the operations to be performed during the transaction. Upon completion, a new profile is created, but previous generations of the profile remain available, should the user want to roll back. For each user, a symlink to the user's default profile is automatically created in @file{$HOME/.guix-profile}. This symlink always points to the current generation of the user's default profile. Thus, users can add @file{$HOME/.guix-profile/bin} to their @code{PATH} environment variable, and so on. In a multi-user setup, user profiles must be stored in a place registered as a @dfn{garbage-collector root}, which @file{$HOME/.guix-profile} points to (@pxref{Invoking guix gc}). That directory is normally @code{@var{localstatedir}/profiles/per-user/@var{user}}, where @var{localstatedir} is the value passed to @code{configure} as @code{--localstatedir}, and @var{user} is the user name. It must be created by @code{root}, with @var{user} as the owner. When it does not exist, or is not owned by @var{user}, @command{guix package} emits an error about it. The @var{options} can be among the following: @table @code @item --install=@var{package} @itemx -i @var{package} Install @var{package}. @var{package} may specify either a simple package name, such as @code{guile}, or a package name followed by a hyphen and version number, such as @code{guile-1.8.8}. If no version number is specified, the newest available version will be selected. In addition, @var{package} may contain a colon, followed by the name of one of the outputs of the package, as in @code{gcc:doc} or @code{binutils-2.22:lib} (@pxref{Packages with Multiple Outputs}). @cindex propagated inputs Sometimes packages have @dfn{propagated inputs}: these are dependencies that automatically get installed along with the required package. An example is the GNU MPC library: its C header files refer to those of the GNU MPFR library, which in turn refer to those of the GMP library. Thus, when installing MPC, the MPFR and GMP libraries also get installed in the profile; removing MPC also removes MPFR and GMP---unless they had also been explicitly installed independently. Besides, packages sometime rely on the definition of environment variables for their search paths (see explanation of @code{--search-paths} below.) Any missing or possibly incorrect environment variable definitions are reported here. @c XXX: keep me up-to-date Finally, when installing a GNU package, the tool reports the availability of a newer upstream version. In the future, it may provide the option of installing directly from the upstream version, even if that version is not yet in the distribution. @item --install-from-expression=@var{exp} @itemx -e @var{exp} Install the package @var{exp} evaluates to. @var{exp} must be a Scheme expression that evaluates to a @code{} object. This option is notably useful to disambiguate between same-named variants of a package, with expressions such as @code{(@@ (gnu packages base) guile-final)}. Note that this option installs the first output of the specified package, which may be insufficient when needing a specific output of a multiple-output package. @item --remove=@var{package} @itemx -r @var{package} Remove @var{package}. @item --upgrade[=@var{regexp}] @itemx -u [@var{regexp}] Upgrade all the installed packages. When @var{regexp} is specified, upgrade only installed packages whose name matches @var{regexp}. Note that this upgrades package to the latest version of packages found in the distribution currently installed. To update your distribution, you should regularly run @command{guix pull} (@pxref{Invoking guix pull}). @item --roll-back Roll back to the previous @dfn{generation} of the profile---i.e., undo the last transaction. When combined with options such as @code{--install}, roll back occurs before any other actions. When rolling back from the first generation that actually contains installed packages, the profile is made to point to the @dfn{empty profile}, also known as @dfn{profile zero}---i.e., it contains no files apart from its own meta-data. Installing, removing, or upgrading packages from a generation that has been rolled back to overwrites previous future generations. Thus, the history of a profile's generations is always linear. @item --search-paths @cindex search paths Report environment variable definitions, in Bash syntax, that may be needed in order to use the set of installed packages. These environment variables are used to specify @dfn{search paths} for files used by some of the installed packages. For example, GCC needs the @code{CPATH} and @code{LIBRARY_PATH} environment variables to be defined so it can look for headers and libraries in the user's profile (@pxref{Environment Variables,,, gcc, Using the GNU Compiler Collection (GCC)}). If GCC and, say, the C library are installed in the profile, then @code{--search-paths} will suggest setting these variables to @code{@var{profile}/include} and @code{@var{profile}/lib}, respectively. @item --profile=@var{profile} @itemx -p @var{profile} Use @var{profile} instead of the user's default profile. @item --dry-run @itemx -n Show what would be done without actually doing it. @item --fallback When substituting a pre-built binary fails, fall back to building packages locally. @item --no-substitutes @itemx --max-silent-time=@var{seconds} Same as for @command{guix build} (@pxref{Invoking guix build}). @item --verbose Produce verbose output. In particular, emit the environment's build log on the standard error port. @item --bootstrap Use the bootstrap Guile to build the profile. This option is only useful to distribution developers. @end table In addition to these actions @command{guix package} supports the following options to query the current state of a profile, or the availability of packages: @table @option @item --search=@var{regexp} @itemx -s @var{regexp} List the available packages whose synopsis or description matches @var{regexp}. Print all the meta-data of matching packages in @code{recutils} format (@pxref{Top, GNU recutils databases,, recutils, GNU recutils manual}). This allows specific fields to be extracted using the @command{recsel} command, for instance: @example $ guix package -s malloc | recsel -p name,version name: glibc version: 2.17 name: libgc version: 7.2alpha6 @end example @item --list-installed[=@var{regexp}] @itemx -I [@var{regexp}] List currently installed packages in the specified profile. When @var{regexp} is specified, list only installed packages whose name matches @var{regexp}. For each installed package, print the following items, separated by tabs: the package name, its version string, the part of the package that is installed (for instance, @code{out} for the default output, @code{include} for its headers, etc.), and the path of this package in the store. @item --list-available[=@var{regexp}] @itemx -A [@var{regexp}] List packages currently available in the software distribution (@pxref{GNU Distribution}). When @var{regexp} is specified, list only installed packages whose name matches @var{regexp}. For each package, print the following items separated by tabs: its name, its version string, the parts of the package (@pxref{Packages with Multiple Outputs}), and the source location of its definition. @end table @node Packages with Multiple Outputs @section Packages with Multiple Outputs @cindex multiple-output packages @cindex package outputs Often, packages defined in Guix have a single @dfn{output}---i.e., the source package leads exactly one directory in the store. When running @command{guix package -i glibc}, one installs the default output of the GNU libc package; the default output is called @code{out}, but its name can be omitted as shown in this command. In this particular case, the default output of @code{glibc} contains all the C header files, shared libraries, static libraries, Info documentation, and other supporting files. Sometimes it is more appropriate to separate the various types of files produced from a single source package into separate outputs. For instance, the GLib C library (used by GTK+ and related packages) installs more than 20 MiB of reference documentation as HTML pages. To save space for users who do not need it, the documentation goes to a separate output, called @code{doc}. To install the main GLib output, which contains everything but the documentation, one would run: @example guix package -i glib @end example The command to install its documentation is: @example guix package -i glib:doc @end example Some packages install programs with different ``dependency footprints''. For instance, the WordNet package install both command-line tools and graphical user interfaces (GUIs). The former depend solely on the C library, whereas the latter depend on Tcl/Tk and the underlying X libraries. In this case, we leave the command-line tools in the default output, whereas the GUIs are in a separate output. This allows users who do not need the GUIs to save space. There are several such multiple-output packages in the GNU distribution. Other conventional output names include @code{lib} for libraries and possibly header files, @code{bin} for stand-alone programs, and @code{debug} for debugging information (@pxref{Installing Debugging Files}). The outputs of a packages are listed in the third column of the output of @command{guix package --list-available} (@pxref{Invoking guix package}). @node Invoking guix gc @section Invoking @command{guix gc} @cindex garbage collector Packages that are installed but not used may be @dfn{garbage-collected}. The @command{guix gc} command allows users to explicitly run the garbage collector to reclaim space from the @file{/nix/store} directory. The garbage collector has a set of known @dfn{roots}: any file under @file{/nix/store} reachable from a root is considered @dfn{live} and cannot be deleted; any other file is considered @dfn{dead} and may be deleted. The set of garbage collector roots includes default user profiles, and may be augmented with @command{guix build --root}, for example (@pxref{Invoking guix build}). The @command{guix gc} command has three modes of operation: it can be used to garbage-collect any dead files (the default), to delete specific files (the @code{--delete} option), or to print garbage-collector information. The available options are listed below: @table @code @item --collect-garbage[=@var{min}] @itemx -C [@var{min}] Collect garbage---i.e., unreachable @file{/nix/store} files and sub-directories. This is the default operation when no option is specified. When @var{min} is given, stop once @var{min} bytes have been collected. @var{min} may be a number of bytes, or it may include a unit as a suffix, such as @code{MiB} for mebibytes and @code{GB} for gigabytes. When @var{min} is omitted, collect all the garbage. @item --delete @itemx -d Attempt to delete all the store files and directories specified as arguments. This fails if some of the files are not in the store, or if they are still live. @item --list-dead Show the list of dead files and directories still present in the store---i.e., files and directories no longer reachable from any root. @item --list-live Show the list of live store files and directories. @end table In addition, the references among existing store files can be queried: @table @code @item --references @itemx --referrers List the references (respectively, the referrers) of store files given as arguments. @item --requisites @itemx -R List the requisites of the store files passed as arguments. Requisites include the store files themselves, their references, and the references of these, recursively. In other words, the returned list is the @dfn{transitive closure} of the store files. @end table @node Invoking guix pull @section Invoking @command{guix 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. On completion, @command{guix package} will use packages and package versions from this just-retrieved copy of Guix. Not only that, but all the Guix commands and Scheme modules will also be taken from that latest version. New @command{guix} sub-commands added by the update also become available. The @command{guix pull} command is usually invoked with no arguments, but it supports the following options: @table @code @item --verbose Produce verbose output, writing build logs to the standard error output. @item --bootstrap Use the bootstrap Guile to build the latest Guix. This option is only useful to Guix developers. @end table @c ********************************************************************* @node Programming Interface @chapter Programming Interface 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{/nix/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 derivation 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. This chapter describes all these APIs in turn, starting from high-level package definitions. @menu * Defining Packages:: Defining new packages. * The Store:: Manipulating the package store. * Derivations:: Low-level interface to package derivations. @end menu @node Defining Packages @section Defining Packages 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 (use-modules (guix packages) (guix download) (guix build-system gnu) (guix licenses)) (define hello (package (name "hello") (version "2.8") (source (origin (method url-fetch) (uri (string-append "mirror://gnu/hello/hello-" version ".tar.gz")) (sha256 (base32 "0wqd8sjmxfskrflaxywc7gqw7sfawrfvdxd9skxawzfgyy0pzdz6")))) (build-system gnu-build-system) (inputs `(("gawk" ,gawk))) (synopsis "GNU Hello") (description "Yeah...") (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 variable @var{hello} to a @code{} 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"}. There are a few points worth noting in the above package definition: @itemize @item The @code{source} field of the package is an @code{} object. 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{Invoking guix download}) and @code{guix hash} (@pxref{Invoking guix hash}). @item @cindex GNU Build System The @code{build-system} field is set to @var{gnu-build-system}. The @var{gnu-build-system} variable is defined in the @code{(guix build-system gnu)} module, and is bound to a @code{} object. Naturally, @var{gnu-build-system} represents the familiar GNU Build System, and variants thereof (@pxref{Configuration, configuration and makefile conventions,, standards, GNU Coding Standards}). In a nutshell, packages using the GNU Build System may be configured, built, and installed with the usual @code{./configure && make && make check && make install} command sequence. This is what @var{gnu-build-system} does. In addition, @var{gnu-build-system} ensures that the ``standard'' environment for GNU packages is available. This includes tools such as GCC, Coreutils, Bash, Make, Diffutils, and Patch. @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{} object. 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. 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 There are other fields that package definitions may provide. Of particular interest is the @code{arguments} field. When specified, it must be bound to a list of additional arguments to be passed to the build system. For instance, the above definition could be augmented with the following field initializer: @example (arguments `(#:tests? #f #:configure-flags '("--enable-silent-rules"))) @end example @noindent These are keyword arguments (@pxref{Optional Arguments, keyword arguments in Guile,, guile, GNU Guile Reference Manual}). They are passed to @var{gnu-build-system}, which interprets them as meaning ``do not run @code{make check}'', and ``run @file{configure} with the @code{--enable-silent-rules} flag''. The value of these keyword parameters is actually evaluated in the @dfn{build stratum}---i.e., by a Guile process launched by the daemon (@pxref{Derivations}). Once a package definition is in place@footnote{Simple package definitions like the one above may be automatically converted from the Nixpkgs distribution using the @command{guix import} command.}, the package may actually be built using the @code{guix build} command-line tool (@pxref{Invoking guix build}). Eventually, updating the package definition to a new upstream version can be partly automated by the @command{guix refresh} command (@pxref{Invoking guix refresh}). Behind the scenes, a derivation corresponding to the @code{} object is first computed by the @code{package-derivation} procedure. That derivation is stored in a @code{.drv} file under @file{/nix/store}. The build actions it prescribes may then be realized by using the @code{build-derivations} procedure (@pxref{The Store}). @deffn {Scheme Procedure} package-derivation @var{store} @var{package} [@var{system}] Return the derivation path and corresponding @code{} object of @var{package} for @var{system} (@pxref{Derivations}). @var{package} must be a valid @code{} 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{The 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 derivation path and corresponding @code{} 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 @node The Store @section The Store @cindex store @cindex store paths Conceptually, the @dfn{store} is where derivations that have been successfully built are stored---by default, under @file{/nix/store}. Sub-directories in the store are referred to as @dfn{store paths}. The store has an associated database that contains information such has the store paths referred to by each store path, and the list of @emph{valid} store paths---paths that result from a successful build. The store is always accessed by the daemon on behalf of its clients (@pxref{Invoking guix-daemon}). To manipulate the store, clients connect to the daemon over a Unix-domain socket, send it requests, and read the result---these are remote procedure calls, or RPCs. The @code{(guix store)} module provides procedures to connect to the daemon, and to perform RPCs. These are described below. @deffn {Scheme Procedure} open-connection [@var{file}] [#:reserve-space? #t] Connect to the daemon over the Unix-domain socket at @var{file}. 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} Return @code{#t} when @var{path} is a valid store path. @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 derivation paths), and return when the worker is done building them. Return @code{#t} on success. @end deffn @c FIXME @i{This section is currently incomplete.} @node Derivations @section Derivations @cindex derivations Low-level build actions and the environment in which they are performed are represented by @dfn{derivations}. A derivation contain 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{The Store}). 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{system} @var{builder} @var{args} @var{env-vars} @var{inputs} [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] [#:hash-mode #f] Build a derivation with the given arguments. Return the resulting store path and @code{} object. When @var{hash}, @var{hash-algo}, and @var{hash-mode} are given, a @dfn{fixed-output derivation} is created---i.e., one whose result is known in advance, such as a file download. @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)) (call-with-values (lambda () (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" (%current-system) bash `("-e" ,builder) '(("HOME" . "/homeless")) '()))) list) @result{} ("/nix/store/@dots{}-foo.drv" #< @dots{}>) @end lisp As can be guessed, this primitive is cumbersome to use directly. An improved variant is @code{build-expression->derivation}, which allows the caller to directly pass a Guile expression as the build script: @deffn {Scheme Procedure} build-expression->derivation @var{store} @var{name} @var{system} @var{exp} @var{inputs} [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] [#:env-vars '()] [#:modules '()] [#: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. @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 /nix/store/@dots{}-goo (call-with-output-file (string-append out "/test") (lambda (p) (display '(hello guix) p)))))) (build-expression->derivation store "goo" (%current-system) builder '())) @result{} "/nix/store/@dots{}-goo.drv" @result{} #< @dots{}> @end lisp @cindex strata of code Remember that the build expression passed to @code{build-expression->derivation} is run by a separate Guile process than the one that calls @code{build-expression->derivation}: it is run by a Guile process launched by the daemon, typically in a chroot. So, while there is a single language for both the @dfn{host} and the build side, there are really two @dfn{strata} of code: the host-side, and the build-side code@footnote{The term @dfn{stratum} in this context was coined by Manuel Serrano et al. in the context of their work on Hop.}. This distinction is important to keep in mind, notably when using higher-level constructs such as @var{gnu-build-system} (@pxref{Defining Packages}). For this reason, Guix modules that are meant to be used in the build stratum are kept in the @code{(guix build @dots{})} name space. @c ********************************************************************* @node Utilities @chapter Utilities This section describes tools primarily targeted at developers and users who write new package definitions. They complement the Scheme programming interface of Guix in a convenient way. @menu * Invoking guix build:: Building packages from the command line. * Invoking guix download:: Downloading a file and printing its hash. * Invoking guix hash:: Computing the cryptographic hash of a file. * Invoking guix refresh:: Updating package definitions. @end menu @node Invoking guix build @section Invoking @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{Invoking 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 @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{/nix/store/@dots{}-coreutils-8.19.drv}. Alternatively, the @code{--expression} option may be used to specify a Scheme expression that evaluates to a package; this is useful when disambiguation among several same-named packages or package variants is needed. The @var{options} may be zero or more of the following: @table @code @item --expression=@var{expr} @itemx -e @var{expr} Build the package @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. @item --source @itemx -S Build the packages' source derivations, rather than the packages themselves. For instance, @code{guix build -S gcc} returns something like @file{/nix/store/@dots{}-gcc-4.7.2.tar.bz2}, which is GCC's source tarball. @item --system=@var{system} @itemx -s @var{system} Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of the host's system type. 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 allows users to build packages in a complete 32-bit environment. @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{Configuration Names, GNU configuration triplets,, configure, GNU Configure and Build System}). @item --derivations @itemx -d Return the derivation paths, not the output paths, of the given packages. @item --keep-failed @itemx -K Keep the build tree of failed builds. Thus, if a build fail, 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. @item --dry-run @itemx -n Do not build the derivations. @item --fallback When substituting a pre-built binary fails, fall back to building packages locally. @item --no-substitutes Build instead of resorting to pre-built substitutes. @item --max-silent-time=@var{seconds} When the build or substitution process remains silent for more than @var{seconds}, terminate it and report a build failure. @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 --root=@var{file} @itemx -r @var{file} Make @var{file} a symlink to the result, and register it as a garbage collector root. @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. @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 store)} module. @node Invoking guix download @section Invoking @command{guix download} When writing a package definition, developers typically need to download the package's source tarball, compute its SHA256 hash, and write that hash in the package definition (@pxref{Defining Packages}). 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{Invoking 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. The following option is 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}, @ref{Invoking guix hash}. @end table @node Invoking guix hash @section Invoking @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{Defining Packages}). The general syntax is: @example guix hash @var{option} @var{file} @end example @command{guix hash} has the following option: @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. @end table @node Invoking guix refresh @section Invoking @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 It does so by browsing each package's FTP directory and determining the highest version number of the source tarballs therein@footnote{Currently, this only works for GNU packages.}. When passed @code{--update}, it modifies distribution source files to update the version numbers and source tarball hashes of those packages' recipes (@pxref{Defining Packages}). 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 it's 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 --update @itemx -u Update distribution source files (package recipes) in place. @ref{Defining Packages}, 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. @end table In addition, @command{guix refresh} can be passed one or more package names, as in this example: @example guix refresh -u emacs idutils @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. The following options can be used to customize GnuPG operation: @table @code @item --key-server=@var{host} Use @var{host} as the OpenPGP key server when importing a public key. @item --gpg=@var{command} Use @var{command} as the GnuPG 2.x command. @var{command} is searched for in @code{$PATH}. @end table @c ********************************************************************* @node GNU Distribution @chapter GNU Distribution Guix comes with a distribution 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}.} that form the basis of the GNU system. This includes 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 seen by running @command{guix package} (@pxref{Invoking guix package}): @example guix package --list-available @end example Our goal is to build 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. @menu * Packaging Guidelines:: What goes into the distribution. * Installing Debugging Files:: Feeding the debugger. * Package Modules:: Packages from the programmer's viewpoint. * Bootstrapping:: GNU/Linux built from scratch. * Porting:: Targeting another platform or kernel. @end menu Building this distribution is a cooperative effort, and you are invited to join! @ref{Contributing}, for information about how you can help. @node Packaging Guidelines @section Packaging Guidelines @c Adapted from http://www.gnu.org/philosophy/philosophy.html. 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. @node Installing Debugging Files @section Installing 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{Packages with Multiple Outputs}). 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 -i 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}. @c XXX: keep me up-to-date The @code{debug} output mechanism in Guix is implemented by the @code{gnu-build-system} (@pxref{Defining Packages}). Currently, it is opt-in---debugging information is available only for those packages whose definition explicitly declares 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{Invoking guix package}). @node Package Modules @section Package Modules From a programming viewpoint, the package definitions of the distribution are provided by Guile modules in the @code{(gnu packages ...)} name space---for instance, the @code{(gnu packages emacs)} module exports a variable named @code{emacs}, which is bound to a @code{} object (@pxref{Defining Packages}). The @code{(gnu packages)} module provides facilities for searching for packages. 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. More on this in the next section. @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{Introduction}). 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{Derivations}). 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,,,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. 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{The 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{Derivations}). 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 @c TODO: Add a package-level dependency graph generated from (gnu @c packages base). 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{/nix/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 base)} module. @c See . The first tool that gets built with the bootstrap binaries is GNU Make, 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 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} variables of the @code{(gnu packages base)} module, and are implicitly used by any package that uses @code{gnu-build-system} (@pxref{Defining Packages}). @unnumberedsubsec Building the 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. @node Porting @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 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 ********************************************************************* @node Contributing @chapter Contributing This project is a cooperative effort, and we need your help to make it grow! Please get in touch with us on @email{guix-devel@@gnu.org}. We welcome ideas, bug reports, patches, and anything that may be helpful to the project. Please see the @url{http://git.savannah.gnu.org/cgit/guix.git/tree/HACKING, @file{HACKING} file} that comes with the Guix source code for practical details about contributions. @c ********************************************************************* @node Acknowledgments @chapter Acknowledgments Guix is based on the Nix package manager, which was designed and implemented by Eelco Dolstra. 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. @c ********************************************************************* @node GNU Free Documentation License @appendix GNU Free Documentation License @include fdl-1.3.texi @c ********************************************************************* @node Concept Index @unnumbered Concept Index @printindex cp @node Function Index @unnumbered Function Index @printindex fn @bye @c Local Variables: @c ispell-local-dictionary: "american"; @c End: