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<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
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    <title>GNU Guix, package manager, system distribution and more</title>

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  <body>
    <div class="reveal">
      <div class="slides">
	<section>
          <img src="Guix.svg" style="background: unset; margin: unset; border: unset; box-shadow: unset;">
          <h1>GNU Guix</h1>
          <h2>Package manager,<br> system distribution<br> and more…</h2>

          <aside class="notes" data-markdown>
            Hello, my name is Chris, and we're going to take a look at
            a software project called GNU Guix.

            Before we begin, hands up if you're excited about package
            managers?

            I'd prefer to cover only some of the material I've got,
            really well, rather than cover all of it badly, so please
            interrupt, and jump in with questions as and when they
            come to you.

            I've not planned any live demos explicitly, but I'm using
            GuixSD on this laptop, and am happy to attempt to demo
            stuff.

            I first found out about Guix sometime in late 2015, early
            2016.

            I remember installing it the night before FOSDEM, a free
            software conference in Brussles, back in January 2016. At
            FOSDEM that year there were many talks about Guix in the
            GNU Guile devroom.

            I started using and contributing to Guix soon after.

            Maybe some of you are using Guix already, maybe some of
            you have heard of it, but don't know much about it, and
            maybe some of you haven't heard of Guix before freenode
            live.

            In any case, I hope most of you will learn something about
            Guix in the next hour.

            I'm going to try and cover:
            - some of the technical fundamentals
            - how you can use guix as a package manager
            - how you can use Guix to manage systems and services
            - and finally, ways in which you can extend Guix
        </section>

        <section>
          <h1>
            Guix...
          </h1>
          <h2>
            Why another package management tool?
          </h2>

          <aside class="notes" data-markdown>
            So, Guix is a package management tool. Something that you
            can use to get and use software.

            If you haven't heard of package management tools before,
            think of a package as a somewhat uniform way of dealing
            with different bits software.

            I'm imagining many of you use a package manager, maybe
            even more than one, so why might you want to use Guix?

            Now Guix is a project, involving quite a few people, and I
            imagine there are different views on this, but I've tried
            to sum it up as user control or user freedom.
          </aside>
        </section>

        <section>
          <h1>User<br>Control / Freedom</h1>

          <aside class="notes" data-markdown>
            Installing software is something which I think has been
            getting easier, and better.

            Package managers have helped a lot with this, but often
            there is still room for improvement.

            Sometimes, package managers have the option to install
            software without building it from source by fetching some
            corresponding binary package. But you may want to build
            the software from source anyway, and this can be tricky.

            There can be a few reasons for building from source. There
            might not be a corresponding binary package available, you
            might want to not have to trust the available binary
            packages, or you may want to modify the software, patching
            a security vulnerability for example.

            Also, when installing software, there can be issues with
            package conflicts.

            With some package managers, some packages may conflict
            with others, and some may conflict with different versions
            of the same package. Making it difficult to meet the needs
            of multiple pieces of software, or multiple users.
            
            Even if you make it through installing software, many
            people using software are stuck in a world where if they
            take the risk to remove or upgrade some software on there
            computer, then something may break.

            Now, of course, updating software may introduce bugs, but
            sometimes updating one bit of software can break a related
            bit of software that wasn't updated.

            The same goes for installing and removing software,
            sometimes, unfortunately, some other piece of software
            needed what was removed, or an existing piece of software
            conflicts with the newly installed software.

            On the whole, being able to install software from source,
            or using prebuilt binary packages, avoiding conflicts
            between packages, even multiple versions of the same
            package, and being able to remove or upgrade software,
            without worrying about causing problems are all issues of
            user control and user freedom.
            
            I think Guix is a tool that can help, so how does it work?
          </aside>
        </section>

        <section>
          <h1>How does Guix work?</h1>

          <aside class="notes" data-markdown>
            Before jumping straight in to Guix, there are some
            important concepts to cover first.

            These are not new concepts, to put things in perspective,
            here is a timeline. 
          </aside>
        </section>

        <section>
          <!-- https://codepen.io/Mhmdhasan/pen/mVjpVK -->
          <div class="timeline">
            <div class="timeline-block timeline-block-left" style="height: 50%;">
              <div class="marker"></div>
              <div class="timeline-content">
                <h3>1993</h3>
                First Debian release
                <!-- https://www.debian.org/doc/manuals/project-history/ch-releases.en.html -->
              </div>
            </div>

            <div class="timeline-block timeline-block-right" style="height: 36%;">
              <div class="marker"></div>
              <div class="timeline-content">
                <h3>2004</h3> Nix: A Safe and Policy-Free System for
                Software Deployment
              </div>
            </div>

            <div class="timeline-block timeline-block-left" style="height: 22%;">
              <div class="marker"></div>
              <div class="timeline-content">
                <h3>2012</h3>
                Guix announced
              </div>
            </div>
          </div>

          <div class="timeline-block timeline-block-right">
            <div class="marker"></div>
            <div class="timeline-content">
              <h3>2017</h3>
              freenode #live
            </div>
          </div>

          <aside class="notes" data-markdown>
            At the top, we have Debian. Which started in 1993, and has
            grown to be a very popular free software distribution.

            I love Debian. I've used it quite a bit, including writing
            packages for software and services.

            If I make any comparisons to it, its not because I think
            its bad, just that its what I was using, before I began
            using Guix more and more.

            A while after the Debian project started, and quite a long
            time ago now, back in 2004, the first paper on a piece of
            software called Nix was published.

            I didn't find out about Nix until I found out about Guix,
            but Nix is important to mention, as some of the key
            concepts underlying Guix come from Nix.

            Around 5 years ago now, the Guix project was started bu
            Ludovic Courtès, using some of the key ideas from Nix, and
            adding some more.
          </aside>
        </section>

        <section data-background-color="white">
          <a href="https://nixos.org/~eelco/pubs/nspfssd-lisa2004-final.pdf">
            <img class="noborder" src="nix-paper-2004.png">
          </a>

          <aside class="notes" data-markdown>
            As I said before, the first paper was published in 2004,
            but there is a more detailed description of Nix in Eelco
            Dolstra's PhD thesis, "The Purely Functional Software
            Deployment Model", which was published later in 2006.

            I'm going to have a go at explaining what I think is
            useful to know for understanding how Guix works, but if
            you want a more original and comprehensive description,
            then these papers are the ones to read.
          </aside>
        </section>

        <section>
          <h2>The store</h2>

          <pre class="fragment">/gnu/store/<span class="fragment highlight-current-green">wf65hjwqwpz4wllasn63zysi5irql2sx</span>-hello-2.10
├── bin
│   └── hello
└── share
    ├── info
    │   └── ...
    ├── locale
    │   └── ...
    └── man
        └── ...
</pre>

          <aside class="notes" data-markdown>
            We start with the store, a special directory where files,
            and the outputs from derivations that have been built
            successfully are stored.

            When using Guix, the location of the store is /gnu/store.

            The store contains store items, and there is a database
            that contains information on these, such as how the store
            items refer to each other.

            (Next)

            Shown here is an example store item.

            In this case, its a directory, containing GNU Hello.

            Operations on the store should be performed by the build
            daemon, which helps ensure that the store is maintained
            correctly. To protect the integrity of the store, it is
            useful to make it read only, to everything but the build
            daemon.

            (Next)

            The hash here is really important, and that comes from the
            derivation which is used to create the store item.
          </aside>
        </section>

        <section data-transition="fade-out">
          <code>
            <pre>$ guix build --derivations hello
/gnu/store/1drc59xkcvgdphzgylxm41ln9p5dwbgn-hello-2.10.drv</pre>
          </code>

          <code>
            <small><pre>Derive(
  [("out",<span class="fragment highlight-current-green" data-fragment-index="1">"/gnu/store/<span class="fragment highlight-current-green">wf65hjwqwpz4wllasn63zysi5irql2sx</span>-hello-2.10"</span>,"","")],
  [("/gnu/store/0gabs9i1zawd406rkkr7l15ifg61s34r-glibc-2.25.drv",["out"]),
   ("/gnu/store/1lqw4mz8xzjhnb65kc1nvk8wg39spv5j-hello-2.10.tar.gz.drv",["out"]),
   ("/gnu/store/1vmhamqwgs3qa7rw28am5rm3b9fjs163-file-5.30.drv",["out"]),
   ("/gnu/store/23h9fzinl5j1s5x7r2i155f1m7ify9wl-ld-wrapper-0.drv",["out"]),
   ("/gnu/store/3li1y3cc8rkr4d0q9h8bkvl4h3macnf6-bash-minimal-4.4.12.drv",["out"]),
   ("/gnu/store/6y5h0pbqci67ql1ij5crkchjzmxkafbv-gawk-4.1.4.drv",["out"]),
   ("/gnu/store/8xmbpyfnh5cdrk9fmx8j67894bq9vl1r-module-import.drv",["out"]),
   ("/gnu/store/9sahk6fh2p5k631rxl6amx0cd4z8jn0s-diffutils-3.6.drv",["out"]),
   ("/gnu/store/cm2f8yxfpy353kxbq5gl7whzvmkl9niv-make-4.2.1.drv",["out"]),
   ("/gnu/store/fqx5lcb8lhdxkw1dwcgahnqaxgaycgb1-tar-1.29.drv",["out"]),
   ("/gnu/store/i5fzg4cq88yvl2i7bsnqprzgq494bpdm-patch-2.7.5.drv",["out"]),
   ("/gnu/store/iwzysdzl3yphqa0c0km8liiimcsrxmvd-glibc-utf8-locales-2.25.drv",["out"]),
   ("/gnu/store/jwsvpyyxkmyg0wk3cic3b9q9wgimphkz-findutils-4.6.0.drv",["out"]),
   ("/gnu/store/m5kd44n51ns8zlc8mvii497xc2siydpb-coreutils-8.27.drv",["out"]),
   ("/gnu/store/pjgbs80jhzpm7lfpsa5dp6jgxkcv6n56-bzip2-1.0.6.drv",["out"]),
   ("/gnu/store/qgcr4gp3qz098yh6zsnn97dg4h8d2nbn-sed-4.4.drv",["out"]),
   ("/gnu/store/r49cqbngzhn8q1qr6cjsm4vs85vwzl9i-xz-5.2.2.drv",["out"]),
   ("/gnu/store/rkjydj936a096s70bxq7sz77bbxzfqvd-gzip-1.8.drv",["out"]),
   ("/gnu/store/vk9xdybvknvnnaxavdk2q43yvdq5h47r-binutils-2.28.drv",["out"]),
   ("/gnu/store/wrlssahrl79njwzwv8clcq8vdh2syppx-module-import-compiled.drv",["out"]),
   ("/gnu/store/xz5ikvwa6pyz11h0a5hmzf9rxyi5xjzw-guile-2.2.2.drv",["out"]),
   ("/gnu/store/zb0wzrfgiydmr8gbxywyrmg6yp68w4fj-linux-libre-headers-4.4.47.drv",["out"]),
   ("/gnu/store/zxiy6cnd05p90hmyk1mvr30lm17ghwim-grep-3.0.drv",["out"]),
   ("/gnu/store/zxkwsk4g0m7j2p54l7xp2gblb6v4zddf-gcc-5.4.0.drv",["out"])],
  ["/gnu/store/hqlhinp4gsfym9l5bq63c7g8y1j14ynz-hello-2.10-guile-builder"],
   "x86_64-linux",
   "/gnu/store/d8gkn84yqacjr80pzicz1ka3y2s1f2x0-guile-2.2.2/bin/guile",
  ["--no-auto-compile",
   "-L",
   "/gnu/store/xhwmxry8kkmq7897558qmcmfsx8r1z45-module-import",
   "/gnu/store/hqlhinp4gsfym9l5bq63c7g8y1j14ynz-hello-2.10-guile-builder"],
  [("GUILE_LOAD_COMPILED_PATH","/gnu/store/r7sf4w2wwrbxbcf04pi9a5gkdhzaya2g-module-import-compiled"),
   ("out",<span class="fragment highlight-current-green" data-fragment-index="1">"/gnu/store/wf65hjwqwpz4wllasn63zysi5irql2sx-hello-2.10"</span>)]
)</pre></small>
          </code>

          <aside class="notes" data-markdown>
            This is an example derivation for the GNU hello package.

            Normally, there is no formatting or highlighting, but I've
            added some here to make it more understandable.

            (Next)
            
            The first thing to notice is the output file, highlighted
            here in green. It appears twice, the first time is for the
            build daemon, so it knows what to expect, and the second
            time is for the builder, so it knows where to put the
            output.

            The hash part of the filename is computed by hashing
            something which looks like this, but not containing the
            output file, as you haven't computed the hash yet.
            
            So lets remove the output file, and look at what goes in
            to the hash.
          </aside>
        </section>

        <section data-transition="fade">
          <pre>$ guix build --derivations hello
/gnu/store/1drc59xkcvgdphzgylxm41ln9p5dwbgn-hello-2.10.drv</pre>

          <small><pre>Derive(
  [("out",<span class="fragment highlight-current-red" data-fragment-index="1">""</span>,"","")],
  <span class="fragment highlight-current-green">[("/gnu/store/0gabs9i1zawd406rkkr7l15ifg61s34r-glibc-2.25.drv",["out"]),
   ("/gnu/store/1lqw4mz8xzjhnb65kc1nvk8wg39spv5j-hello-2.10.tar.gz.drv",["out"]),
   ("/gnu/store/1vmhamqwgs3qa7rw28am5rm3b9fjs163-file-5.30.drv",["out"]),
   ("/gnu/store/23h9fzinl5j1s5x7r2i155f1m7ify9wl-ld-wrapper-0.drv",["out"]),
   ("/gnu/store/3li1y3cc8rkr4d0q9h8bkvl4h3macnf6-bash-minimal-4.4.12.drv",["out"]),
   ("/gnu/store/6y5h0pbqci67ql1ij5crkchjzmxkafbv-gawk-4.1.4.drv",["out"]),
   ("/gnu/store/8xmbpyfnh5cdrk9fmx8j67894bq9vl1r-module-import.drv",["out"]),
   ("/gnu/store/9sahk6fh2p5k631rxl6amx0cd4z8jn0s-diffutils-3.6.drv",["out"]),
   ("/gnu/store/cm2f8yxfpy353kxbq5gl7whzvmkl9niv-make-4.2.1.drv",["out"]),
   ("/gnu/store/fqx5lcb8lhdxkw1dwcgahnqaxgaycgb1-tar-1.29.drv",["out"]),
   ("/gnu/store/i5fzg4cq88yvl2i7bsnqprzgq494bpdm-patch-2.7.5.drv",["out"]),
   ("/gnu/store/iwzysdzl3yphqa0c0km8liiimcsrxmvd-glibc-utf8-locales-2.25.drv",["out"]),
   ("/gnu/store/jwsvpyyxkmyg0wk3cic3b9q9wgimphkz-findutils-4.6.0.drv",["out"]),
   ("/gnu/store/m5kd44n51ns8zlc8mvii497xc2siydpb-coreutils-8.27.drv",["out"]),
   ("/gnu/store/pjgbs80jhzpm7lfpsa5dp6jgxkcv6n56-bzip2-1.0.6.drv",["out"]),
   ("/gnu/store/qgcr4gp3qz098yh6zsnn97dg4h8d2nbn-sed-4.4.drv",["out"]),
   ("/gnu/store/r49cqbngzhn8q1qr6cjsm4vs85vwzl9i-xz-5.2.2.drv",["out"]),
   ("/gnu/store/rkjydj936a096s70bxq7sz77bbxzfqvd-gzip-1.8.drv",["out"]),
   ("/gnu/store/vk9xdybvknvnnaxavdk2q43yvdq5h47r-binutils-2.28.drv",["out"]),
   ("/gnu/store/wrlssahrl79njwzwv8clcq8vdh2syppx-module-import-compiled.drv",["out"]),
   ("/gnu/store/xz5ikvwa6pyz11h0a5hmzf9rxyi5xjzw-guile-2.2.2.drv",["out"]),
   ("/gnu/store/zb0wzrfgiydmr8gbxywyrmg6yp68w4fj-linux-libre-headers-4.4.47.drv",["out"]),
   ("/gnu/store/zxiy6cnd05p90hmyk1mvr30lm17ghwim-grep-3.0.drv",["out"]),
   ("/gnu/store/zxkwsk4g0m7j2p54l7xp2gblb6v4zddf-gcc-5.4.0.drv",["out"])]</span>,
  ["/gnu/store/hqlhinp4gsfym9l5bq63c7g8y1j14ynz-hello-2.10-guile-builder"],
   "x86_64-linux",
   "/gnu/store/d8gkn84yqacjr80pzicz1ka3y2s1f2x0-guile-2.2.2/bin/guile",
  ["--no-auto-compile",
   "-L",
   "/gnu/store/xhwmxry8kkmq7897558qmcmfsx8r1z45-module-import",
   "/gnu/store/hqlhinp4gsfym9l5bq63c7g8y1j14ynz-hello-2.10-guile-builder"],
  [("GUILE_LOAD_COMPILED_PATH","/gnu/store/r7sf4w2wwrbxbcf04pi9a5gkdhzaya2g-module-import-compiled"),
   ("out",<span class="fragment highlight-current-red" data-fragment-index="1">""</span>)]
)</pre></small>

          <aside class="notes" data-markdown>
            (Next)

            So the output file has now been removed, here highlighted
            in red.

            (Next)

            One more processing step takes place before this data in
            hashed. The input derivation files, shown in the green
            area are replaced with the hash for the corresponding
            derivation, computed through the same process that we are
            currently going through.
          </aside>
        </section>

        <section data-transition="fade-in">
          <pre>$ guix build --derivations hello
/gnu/store/1drc59xkcvgdphzgylxm41ln9p5dwbgn-hello-2.10.drv</pre>

          <small><pre>Derive(
  [("out","","","")],
  <span class="fragment highlight-current-green">[("04fb79c7338393b15562c5ffd222b40fb745683896789ad2b37659ac9d597540",["out"]),
   ("08a81b5317696b0ac342330b4561409db5db8273fee477c26cd2854499e4be1c",["out"]),
   ("0fcc386963a58070aacfc0cfb4fa5e67e676b25b6b038ed1aa61f12b933a39c3",["out"]),
   ("1b6c42938b2a02480294d8e89bf9fe94c77f392fd41f7cdb72b4c85071b3d197",["out"]),
   ("1e8dc40cc0593bae81806df0a1785582fb94ee07802b095ad521e7cb0dd16c41",["out"]),
   ("2e25667c193bed7410ca1f675ba717d5aec59123392d14b35d0918287de2fdf4",["out"]),
   ("3266b64f962b87ed7bb437ddd49c33a20d439e049a3829e2c10f5c2d8ae7d294",["out"]),
   ("39ea9f7baeee4ba446ebbaed88b5354adc088dae479e73a2825471c07088a86c",["out"]),
   ("522962e0ca0c7a5682ee561e618c9e08ce841d24468125c203e935ecd0e8da37",["out"]),
   ("523610101af5dc2481bdce53a050d680bbc516c64baf32463cf95ab3b18aa261",["out"]),
   ("5d7766754e92a0a96ca3b732ae0d9e3da892994961cee1500d7c689a0ddcb785",["out"]),
   ("61fd1308247835184ffe88140f9025117edb3210c47d617feafa33572ad8b8e3",["out"]),
   ("6ae6f3630665d92a495a4edb0f337fe1884fff9e6adcef65cf1c79131071d127",["out"]),
   ("7b8ef27665067602e4e27e801c6e8f385bd83b378037a60a4f5953a02b12c74f",["out"]),
   ("81c2221261670003975a89df35fba774c3871f4444c0d3a1eef6ef21e7aba678",["out"]),
   ("875b4153b80df041b31b6d0fb93b4bb8b62fbd3938320a8ce6ff263d01b3a536",["out"]),
   ("89e81aee370115bec522ad48de0f59030f227fe8a599bb409352a34e710669f8",["out"]),
   ("a127853978c101a2b52071108ed48834435c0bbaf1b707c13304ef9d8e70c3a6",["out"]),
   ("ab4bf18925deebcc80259b45cba39b348320a03f61d93e2246dcd6f5d28a1b68",["out"]),
   ("afe40de343b27326b5e6089c8adf8fdbdb105dcc35f671025c87de0bba965184",["out"]),
   ("bc726d150b4ba6aa8624eba59ad092d729705de4f0148391d33dac15a8aa5dbf",["out"]),
   ("bfb16f9021e341594cfce1c772ccd491599694460ac1df24a8bb77fadc2a4a04",["out"]),
   ("e226a8e968c6132524948d4fd0483a16603b57bddc92f97d6ce31580889754c2",["out"]),
   ("f662215314a37fcf8ae79e425bd197b3a3351bd8ff3d90506cc069c83c833b6d",["out"])],</span>
  ["/gnu/store/hqlhinp4gsfym9l5bq63c7g8y1j14ynz-hello-2.10-guile-builder"],
   "x86_64-linux",
   <span class="fragment highlight-current-green">"/gnu/store/d8gkn84yqacjr80pzicz1ka3y2s1f2x0-guile-2.2.2/bin/guile",
  ["--no-auto-compile",
   "-L",
   "/gnu/store/xhwmxry8kkmq7897558qmcmfsx8r1z45-module-import",
   "/gnu/store/hqlhinp4gsfym9l5bq63c7g8y1j14ynz-hello-2.10-guile-builder"]</span>,
  <span class="fragment highlight-current-green">[("GUILE_LOAD_COMPILED_PATH","/gnu/store/r7sf4w2wwrbxbcf04pi9a5gkdhzaya2g-module-import-compiled"),
   ("out","")]</span>
)</pre></small>
          <span class="fragment"><!-- Null fragment to end --></span>

          <aside class="notes" data-markdown>
            This is now what is actually hashed, just without any
            formatting.

            (Next)

            The key parts are the hashes of all the input derivations.

            (Next)

            The description of the build process.

            (Next)

            And finally, the environment variables.

            (Next)

            When this derivation is handed over to the build daemon,
            it will run the build process in an isolated
            environment. The build process will only be able to read
            from the areas of the store that are inputs to the
            derivation. It will also only be able to write to the
            specified output locations.

            Network access is disabled, to ensure that the process
            isn't able to access the network, avoiding the possibility
            that it depends on something via the network.
          </aside>
        </section>

        <section>
          <code>
            <pre>$ guix build --derivations hello
/gnu/store/1drc59xkcvgdphzgylxm41ln9p5dwbgn-hello-2.10.drv</pre>
          </code>

          <code>
            <small><pre>Derive(
  [("out","/gnu/store/wf65hjwqwpz4wllasn63zysi5irql2sx-hello-2.10","","")],
  [("/gnu/store/0gabs9i1zawd406rkkr7l15ifg61s34r-glibc-2.25.drv",["out"]),
   <span class="fragment highlight-green">("/gnu/store/1lqw4mz8xzjhnb65kc1nvk8wg39spv5j-hello-2.10.tar.gz.drv",["out"])</span>,
   ("/gnu/store/1vmhamqwgs3qa7rw28am5rm3b9fjs163-file-5.30.drv",["out"]),
   ("/gnu/store/23h9fzinl5j1s5x7r2i155f1m7ify9wl-ld-wrapper-0.drv",["out"]),
   ("/gnu/store/3li1y3cc8rkr4d0q9h8bkvl4h3macnf6-bash-minimal-4.4.12.drv",["out"]),
   ("/gnu/store/6y5h0pbqci67ql1ij5crkchjzmxkafbv-gawk-4.1.4.drv",["out"]),
   ("/gnu/store/8xmbpyfnh5cdrk9fmx8j67894bq9vl1r-module-import.drv",["out"]),
   ("/gnu/store/9sahk6fh2p5k631rxl6amx0cd4z8jn0s-diffutils-3.6.drv",["out"]),
   ("/gnu/store/cm2f8yxfpy353kxbq5gl7whzvmkl9niv-make-4.2.1.drv",["out"]),
   ("/gnu/store/fqx5lcb8lhdxkw1dwcgahnqaxgaycgb1-tar-1.29.drv",["out"]),
   ("/gnu/store/i5fzg4cq88yvl2i7bsnqprzgq494bpdm-patch-2.7.5.drv",["out"]),
   ("/gnu/store/iwzysdzl3yphqa0c0km8liiimcsrxmvd-glibc-utf8-locales-2.25.drv",["out"]),
   ("/gnu/store/jwsvpyyxkmyg0wk3cic3b9q9wgimphkz-findutils-4.6.0.drv",["out"]),
   ("/gnu/store/m5kd44n51ns8zlc8mvii497xc2siydpb-coreutils-8.27.drv",["out"]),
   ("/gnu/store/pjgbs80jhzpm7lfpsa5dp6jgxkcv6n56-bzip2-1.0.6.drv",["out"]),
   ("/gnu/store/qgcr4gp3qz098yh6zsnn97dg4h8d2nbn-sed-4.4.drv",["out"]),
   ("/gnu/store/r49cqbngzhn8q1qr6cjsm4vs85vwzl9i-xz-5.2.2.drv",["out"]),
   ("/gnu/store/rkjydj936a096s70bxq7sz77bbxzfqvd-gzip-1.8.drv",["out"]),
   ("/gnu/store/vk9xdybvknvnnaxavdk2q43yvdq5h47r-binutils-2.28.drv",["out"]),
   ("/gnu/store/wrlssahrl79njwzwv8clcq8vdh2syppx-module-import-compiled.drv",["out"]),
   ("/gnu/store/xz5ikvwa6pyz11h0a5hmzf9rxyi5xjzw-guile-2.2.2.drv",["out"]),
   ("/gnu/store/zb0wzrfgiydmr8gbxywyrmg6yp68w4fj-linux-libre-headers-4.4.47.drv",["out"]),
   ("/gnu/store/zxiy6cnd05p90hmyk1mvr30lm17ghwim-grep-3.0.drv",["out"]),
   ("/gnu/store/zxkwsk4g0m7j2p54l7xp2gblb6v4zddf-gcc-5.4.0.drv",["out"])],
  ["/gnu/store/hqlhinp4gsfym9l5bq63c7g8y1j14ynz-hello-2.10-guile-builder"],
   "x86_64-linux",
   "/gnu/store/d8gkn84yqacjr80pzicz1ka3y2s1f2x0-guile-2.2.2/bin/guile",
  ["--no-auto-compile",
   "-L",
   "/gnu/store/xhwmxry8kkmq7897558qmcmfsx8r1z45-module-import",
   "/gnu/store/hqlhinp4gsfym9l5bq63c7g8y1j14ynz-hello-2.10-guile-builder"],
  [("GUILE_LOAD_COMPILED_PATH","/gnu/store/r7sf4w2wwrbxbcf04pi9a5gkdhzaya2g-module-import-compiled"),
   ("out","/gnu/store/wf65hjwqwpz4wllasn63zysi5irql2sx-hello-2.10")]
)</pre></small>
          </code>

          <aside class="notes" data-markdown>
            Going back to the original derivation, one of the inputs
            is the release of GNU Hello.

            (Next)

            It's shown here in green.
          </aside>
        </section>

        <section>
          <h2>Fixed-output derivation</h2>
          <pre>$ guix build -S -d hello
/gnu/store/1lqw4mz8xzjhnb65kc1nvk8wg39spv5j-hello-2.10.tar.gz.drv</pre>
          <small>
            <pre>Derive(
  [("out",
    <span class="fragment highlight-current-green">"/gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz",
    "sha256",
    "31e066137a962676e89f69d1b65382de95a7ef7d914b8cb956f41ea72e0f516b"</span>)],
  [],
  ["/gnu/store/qivc6nybj6mxa95h7h10hg7qv81rdfcm-mirrors",
   "/gnu/store/wvbspgpk15aq6kcf2f67xjai1fbkbyqc-content-addressed-mirrors"],
  "x86_64-linux",
  "builtin:download",
  [],
  [("content-addressed-mirrors","/gnu/store/wvbspgpk15aq6kcf2f67xjai1fbkbyqc-content-addressed-mirrors"),
   ("impureEnvVars","http_proxy https_proxy LC_ALL LC_MESSAGES LANG COLUMNS"),
   ("mirrors","/gnu/store/qivc6nybj6mxa95h7h10hg7qv81rdfcm-mirrors"),
   ("out","/gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz"),
   ("preferLocalBuild","1"),
   ("url","\"mirror://gnu/hello/hello-2.10.tar.gz\"")]
)</pre></small>

          <aside class="notes" data-markdown>
            The derivation for building the hello package that we've
            just looked at is one type of derivation, but there is
            another.

            This derivation is a fixed output derivation. Unlike the
            previous derivation, it can access the network.

            The compromise here is that the output must be known in
            advance.

            (Next)

            Here, highlighted in green is the file that this
            derivation will create, as well as the hash value and
            algorithm.

            Derivations and fixed output derivations are the building
            blocks that both Nix and Guix use to populate the store
            with software.
          </aside>
        </section>

        <section data-background-color="white">
          <img class="noborder" src="hello-derivation-graph.svg">
          <span class="caption">
            Derivation graph for the hello package
          </span>

          <aside class="notes" data-markdown>
            Here is the bigger picture. This is the graph of
            derivations, both with fixed output and non-fixed output
            derivations.

            If you can make it out, the fixed output derivations are
            in black, and the other derivations are in purple.

            The fixed output derivations tend to sit around the edge
            of the graph, as they describe the building blocks used in
            the other derivations.

            Fixed output derivations are used to describe the source
            code of software, e.g. a source tarball or git repository
            checkout.

            There are also bootstrap binaries in the graph. You can't
            just go from source code, with no compiler, to compiling a
            compiler, so Guix includes some bootstrap binaries to get
            started with.

            Other fixed output derivations include patches that are
            applied to source code, the build scripts, and Guile
            modules that are used in the build scripts.

            This graph also includes the Guix bootstraping process,
            for getting from the bootstrap binaries, to GNU hello, and
            everything in between.

            Also, thinking back to what goes in to the hash for the
            outout of a derivation, that is the hashes of the input
            derivations, the build process and environment variables
            for non-fixed output derivations, and the output name,
            hash algorithm and value for fixed output derivations, we
            can now start to look at when changes happen in this
            graph, what will happen to the outputs for derivations.

            For exapmle, if you were to change the source code for the
            hello package, that would mean that the hash would be
            different, therefore the hash of the fixed output
            derivation would be different. As that hash is part of the
            hash of the hello derivation, its hash would change as
            well.

            Comparing this with a Debian package for example, which
            would always produce /usr/bin/hello, regardless of the
            source code, the way that the derivations output is
            computed means that having hello in the store twice just
            works.

            While I think it can be useful to understand these low
            level details, Guix provides software and tooling to make
            it easy to manage and manipulate derivations, using higher
            level concepts like packages, build systems and more.
          </aside>
        </section>

        <section>
          <h2>The hello package</h2>

          <small class="stretch"><pre>
            <code class="scheme">(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)
    (synopsis "Hello, GNU world: An example GNU package")
    (description
     "GNU Hello prints the message \"Hello, world!\" and then exits.  It
serves as an example of standard GNU coding practices.  As such, it supports
command-line arguments, multiple languages, and so on.")
    (home-page "https://www.gnu.org/software/hello/")
    (license gpl3+)))</code></pre></small>

          <aside class="notes" data-markdown>
            This is the package for GNU hello, that corresponds to the
            derivation for GNU hello.

            Packages are the term used within Guix for an individual
            bit of software. For example, guix itself is available as
            a package.

            Unless you write some custom code for creating packages,
            this is as simple as they get.

            The complexity of building hello is hidden away entirely
            in the build system, the gnu-build-system in the case of
            GNU hello.
          </aside>
        </section>

        <section>
          <h1>What can you do with Guix?</h1>

          <aside class="notes" data-markdown>
            So far, we've covered the store and derivations.

            These are important, but not what you'd normally be
            concerned with if you're using Guix.
          </aside>
        </section>

        <section>
          <h2>Install a package in to your profile</h2>

          <code>
            guix package -i hello
          </code>

          <aside class="notes" data-markdown>
            So, lets look at how you might actually use the GNU hello
            package.

            Guix is usable as a package manager on an existing GNU +
            Linux system, and also even supports the Hurd I think.

            With Guix, the packages installed by each user are kept
            separate. However, the overhead for this is minimal, as
            everything is still kept in the store. Effectively it
            becomes a two step process, ensure that the package is
            present in the store, and then link to it from the users
            profile.

            This separation means that these commands just affect the
            user that runs them, and not other users on the system.
          </aside>
        </section>

        <section>
          <h2>Upgrade the packages in your profile</h2>

          <code>
            guix package -u
          </code>

          <aside class="notes" data-markdown>
            If you want to update the packages in your profile, you
            can use the -u flag to guix package.

            If you only want to upgrade specific packages, you can put
            them after -u.
          </aside>
        </section>

        <section>
          <h2>Roll back to the previous generation of your profile</h2>

          <code>
            guix package --roll-back
          </code>

          <aside class="notes" data-markdown>
            When you use the guix package command, the installation,
            upgrade and remove operations don't destroy any state.

            This means that you can roll back to previous states,
            providing you haven't explicitly removed them.

            To better explain how this all fits together, here are
            some useful diagrams.
          </aside>
        </section>

        <section data-transition="fade-out">
          <pre>guix package -i samtools bowtie</pre>
          <img class="stretch noborder" src="profile-0.svg">
          <a href="https://git.sv.gnu.org/cgit/guix/maintenance.git/tree/talks/bobkonf2017/profile-0.svg"
             class="caption">
            Modified, © Ricardo Wurmus
          </a>

          <aside class="notes" data-markdown>
            Obviously, knowing this isn't required to use the commands
            I just mentioned, but this is a technical talk, so lets go
            through the details.

            Normally, you'd have a .guix-profile symlink in your home
            directory.

            This symlink then points to a file in /var/guix
            representing the current version of the profile.

            This file is also a symlink, which links to a file in the
            same directory. The name of this file is a number, which
            is the generation of the profile.

            This numbered file, in this case 42, is yet another
            symlink. This symlink finally points to the profile within
            the store.

            Profiles in the store are a way of composing packages. A
            profile contains symlinks to other packages in the store,
            in a convenient directory structure, e.g. all of the files
            in the /bin directory within packages end up in the /bin
            directory of the profile.
          </aside>
        </section>

        <section data-transition="fade">
          <pre>guix package -r bowtie</pre>
          <img class="stretch noborder" src="profile-1.svg">
          <a href="https://git.sv.gnu.org/cgit/guix/maintenance.git/tree/talks/bobkonf2017/profile-1.svg"
             class="caption">
            Modified, © Ricardo Wurmus
          </a>

          <aside class="notes" data-markdown>
            When you tell guix to install, remove or upgrade some
            software, it generates a new generation of your profile,
            and then switches to using it.

            So here, removing the bowtie package means that a new
            profile is generated, without the bowtie package.

            The bowtie package is still in the store, and still
            referenced by the previous generation of the profile.

            The other change made is the guix-profile symlink in
            /var/guix. It changes to point to the new 43rd generation
            of your profile.
          </aside>
        </section>

        <section data-transition="fade-in">
          <pre>guix package --roll-back</pre>
          <img class="stretch noborder" src="rollback.svg">
          <a href="https://git.sv.gnu.org/cgit/guix/maintenance.git/tree/talks/bobkonf2017/rollback.svg"
             class="caption">
            Modified, © Ricardo Wurmus
          </a>

          <aside class="notes" data-markdown>
            If you decide that you didn't want to remove the bowtie
            package, you can roll back to the previous generation of
            your profile.

            Like upgrading, rolling back is atomic, all that is
            required is to make the change is to switch the
            guix-profile symlink in /var/guix to point at the file
            named 42 in that same directory.
          </aside>
        </section>

        <section>
          <h2>Wait a minute, what was installed?</h2>

          <aside class="notes" data-markdown>
            So, we've just covered some of the uses of the guix
            package commands.

            Lets go back to that first command, guix package -i hello.
          </aside>
        </section>

        <section data-background-color="white">
          <code>
            guix package -i hello
          </code>
          <img class="noborder fragment" src="hello-derivation-graph.svg">

          <aside class="notes" data-markdown>
            What did this actually install?

            While this may look ambiguous, just install hello, it
            actually ends up being rather specific.

            The instruction here to install hello will match a
            specific package. If there are multiple packages with the
            name hello, then the version can be used to
            disambiguate. By default, Guix will pick the highest
            version.

            The package describes everything about how to build that
            software, all the way down to the bootstrap binaries.

            (Next)

            When you install hello, you specify hello built through
            the process described in this diagram. Now I guess most
            users of guix will fetch a binary substitute for the hello
            package, and any dependencies they need, rather than going
            through the process of building it.
            
            All of this means that Guix gives you the means to get a
            high degree of reproducibility and determinism when using
            software.

            There is no guarantee that the output will be identical
            bit for bit, but that is something that the Guix project
            is working towards, along with other people and projects
            in the free software community.

            There is however a guarantee that the process will be
            identical.

            The hello package isn't a very good example of this, but
            imagine a more complicated scenario, some software with
            many more dependencies and complexity.

            There is a danger with some approaches that as you make
            changes, other changes occur because of a lack of
            reproducibility.

            With Debian for example, unless you are quite careful with
            the versioned dependency constraints and the available
            packages, there is a potential for new versions of
            software to creep in from repositories that you're using.

            With Guix, providing you are using the same package
            definitions, you'll get the same reproducible process when
            building your software.

            
            <!-- More than "have all the bits"

            Say, one day, you sit down, and have a moment of
            inspiration. You come up with a wonderful mathematical
            proof.

            Obviously, you need other people to be able to reproduce
            these amazing findings.

            You're not going to just take a copy of the final result,
            you're going to set out your workings in detail, so that
            someone else, maybe even you can take this description,
            and inspect it to work out how the proof works.

            If there turns out to be problems, or areas that could be
            improved, you can take your detailed workings, and improve
            them, working forward to generate the same, or an improved
            output.-->
          </aside>
        </section>

        <section>
          <code>
guix environment hello
          </code>

          <aside class="notes" data-markdown>
            The guix package command is one way of using guix, but
            there are other ways.

            The guix environment command is primarily aimed at
            developers working on software, but in general it allows
            you to create more temporary profiles.

            For this command, if you were to run it, a subshell would
            start, which includes all the inputs to the packages
            listed. Here, all the inputs for the hello package, like
            gcc for example.

            For another example, when working on guix itself, I often
            use the guix environment guix command, to get a
            environment in which I can build guix.
          </aside>
        </section>

        <section>
          <code>
            guix environment --ad-hoc hello guile
          </code>
          <br><br>
          <pre class="fragment">/gnu/store/5w8jk6p57l5an1d39lngw560r2bw2dx1-profile/bin
├── guild -> /gnu/store/yih…6fk-guile-2.2.2/bin/guild
├── guile -> /gnu/store/yih…6fk-guile-2.2.2/bin/guile
├── guile-config -> /gnu/store/yih…6fk-guile-2.2.2/bin/guile-config
├── guile-snarf -> /gnu/store/yih…6fk-guile-2.2.2/bin/guile-snarf
├── guile-tools -> /gnu/store/yih…6fk-guile-2.2.2/bin/guile-tools
└── hello -> /gnu/store/wf6…2sx-hello-2.10/bin/hello</pre>

          <aside class="notes" data-markdown>
            With the --ad-hoc argument, you can specify that you don't
            want the inputs for packages, but instead want the
            packages themselves to be in the environment.

            (Next)

            As before, the profile that this creates brings together
            the two packages, as shown here by the symlinks within the
            profile to individual packages.
          </aside>
        </section>

        <section>
          <code>
            guix environment --pure --ad-hoc hello
          </code>

          <aside class="notes" data-markdown>
            The guix environment command supports the --pure
            flag. This will mean that the subshell that you enter
            won't inherit environment variables.

            This can help make the behaviour more predictable, by
            isolating what you do in the environment.
          </aside>
        </section>

        <section>
          <code>
            guix environment --container --ad-hoc hello
          </code>

          <br>
          <pre>$ echo /gnu/store/*
/gnu/store/…-ncurses-6.0      /gnu/store/…-profile
/gnu/store/…-manual-database  /gnu/store/…-gcc-5.4.0-lib
/gnu/store/…-info-dir         /gnu/store/…-bash-4.4.12
/gnu/store/…-readline-7.0     /gnu/store/…-glibc-2.25
/gnu/store/…-hello-2.10       /gnu/store/…-bash-static-4.4.12</pre>

          <aside class="notes" data-markdown>
            You can do more for isolation through.

            The guix environment command has a neat --container
            argument.

            This means that the subshell you enter will be in a new
            mount, pid, ipc, uts, user and network namespace.

            The new mount namespace only gives the environment access
            to the store items that are needed, some default other
            directories, as well as the current working directory.

            Here, I'm using echo to show the files in the store. I
            can't use ls, but coreutils isn't in this
            environment. What is show here is the minimal set of
            packages required to run hello, and also the bash shell in
            which the echo command is running.

            Now, this is only possible because the information about
            the complete dependencies needed to run hello which are
            stored in the database accompanying the store.
          </aside>
        </section>

        <section data-background="white">
          <img src="hello-references-graph.svg">

          <span class="caption">Graph of the hello package references</span>

          <aside class="notes" data-markdown>
            If you graph the hello package references, you get this.

            The hello store item references two other store items
            directly, the lib output of the gcc package, and glibc.

            glibc also references bash-static, so that is included
            here also.
          </aside>
        </section>

        <section>
          <small><pre>$ ldd /gnu/store/wf65hjwqwpz4wllasn63zysi5irql2sx-hello-2.10/bin/hello

linux-vdso.so.1 (0x00007ffece166000)
libgcc_s.so.1 => /gnu/store/3x53yv4v144c9xp02rs64z7j597kkqax-gcc-5.4.0-lib/lib/libgcc_s.so.1 (0x00007fee83076000)
libc.so.6 => /gnu/store/n6nvxlk2j8ysffjh3jphn1k5silnakh6-glibc-2.25/lib/libc.so.6 (0x00007fee82cd7000)
/gnu/store/n6nvxlk2j8ysffjh3jphn1k5silnakh6-glibc-2.25/lib/ld-linux-x86-64.so.2 (0x00007fee8328d000)</pre></small>

          <aside class="notes" data-markdown>
            Lets take a deeper look.

            When the hello store item references the gcc and glibc
            store items, it literally contains references to those
            directories in the binary.

            If you use the ldd command to show the shared libraries
            that are linked against, then you see the exact paths
            being specified.

            This is good for a number of reasons.

            From a reliability point of view, this helps, as hello is
            going to be consistent in the shared libraries that it
            loads. This particular way of using shared libraries, as
            well as other approaches to have store items reference
            each other is one of the tools packages in guix use to
            make the software less vulnerable to change and breakages.

            Another benefit of this is that you are still doing
            dynamic linking. I've heard of people not using dynamic
            linking, and statically linking executables to get some of
            the same benefits that Guix provides, but statically
            linked binaries can consume more disk and memory space,
            Guix I think gives you the best of both worlds, reliable
            dynamic linking.
          </aside>
        </section>

        <section>
          <h2>Guix + Direnv</h2>
          <br><br>

          <code>
            use guix --ad-hoc gcc-toolchain python python-lxml
          </code>
          <br><br>

          <code>
            <pre>$ cd /tmp/foo
direnv: loading .envrc
direnv: using guix --ad-hoc gcc-toolchain python python-lxml
direnv: export +PAGER +PYTHONPATH ~CPLUS_INCLUDE_PATH
               ~C_INCLUDE_PATH ~LIBRARY_PATH ~PATH</pre>
          </code>

          <aside class="notes" data-markdown>
            This is a neat way that I use guix environment, and hook
            it up with another program called direnv.

            direnv is an environment switcher for the shell, and guix
            environment can specify environment variables to load a
            profile. Therefore, you can combine the two so that when
            you enter a directory, direnv will invoke guix to load the
            environment.

            Direnv is configured through using a file named .envrc in
            the directory you want it to be active in.

            The example I'm showing here is to create an environment
            containing gcc-toolchain, python and python-lxml when you
            enter the /tmp/foo directory.
          </aside>
        </section>

        <section>
          <h1>Managing systems and services with Guix</h1>

          <aside class="notes" data-markdown>
            So far, we've covered some of the underlying mechanisms
            that allow Guix to work how it does, and also some of the
            ways it can be used as a package manager, both the guix
            package and guix environment commands.

            This isn't all Guix can offer though, it also includes the
            capabilities to describe entire systems, and the services
            that run on them.

            When used in this way, it can be called GuixSD, the Guix
            system distribution. A distribution of GNU + Linux.
          </aside>
        </section>

        <section>
          <h2>Systems</h2>

          <small class="stretch"><pre><code class="scheme no-max-height">(use-modules (gnu))
(use-service-modules networking ssh)
(use-package-modules screen ssh)

(operating-system
  (host-name "komputilo")
  (timezone "Europe/Berlin")
  (locale "en_US.utf8")

  (bootloader (bootloader-configuration
                (bootloader grub-bootloader)
                (target "/dev/sdX")))
  (file-systems (cons (file-system
                        (device "my-root")
                        (title 'label)
                        (mount-point "/")
                        (type "ext4"))
                      %base-file-systems))

  (users (cons (user-account
                (name "alice")
                (comment "Bob's sister")
                (group "users")
                (supplementary-groups '("wheel"
                                        "audio" "video"))
                (home-directory "/home/alice"))
               %base-user-accounts))

  (packages (cons* screen openssh %base-packages))

  (services (cons* (dhcp-client-service)
                   (service openssh-service-type
                            (openssh-configuration
                              (port-number 2222)))
              %base-services)))</code></pre></small>
          
          <aside class="notes" data-markdown>
            Currently when using GuixSD, you'll probably be using a
            configuration file for the system. Here is a modified
            version of the bare bones example included within Guix.

            This specification allows you to declare a whole load of
            different things about your system, the filesystems,
            users, packages, services and more.

            When using GuixSD, the filesystem is a bit different from
            other distributions.

            You don't by default have a /usr directory. As Guix
            manages packages in per user profiles, with the addition
            of a system profile, managing a stateful /usr directory
            would possibly impact some of the advantages that Guix
            brings.

            That doesn't mean you can't have stateful files in /usr
            though, on this laptop I have /usr/bin/env and
            /usr/share/zoneinfo, as that helps with some software that
            I use.

            Another point to mention about GuixSD is how changes to
            this configuration work.

            Changes work similar to the changes to package profiles,
            there are generations of the system in /var/guix/profiles,
            and to apply a change in the configuration to a system,
            you reconfigure the system to use that configuration.

            This process generates the new system state, and then
            switches to it as atomically as possible. This, along with
            the ability to boot in to previous generations of the
            system make GuixSD very reliable.

            Generations of the system don't only include Linux, but
            other components of the system like services and file
            system configuration.

            I really like this. For example, I reconfigured this
            laptop yesterday, save in the knowledge that if anything
            went wrong, I could just boot in to the previous
            generation of my system.

            Compared to other ways I've managed systems, I think using
            Guix has a lot of advantages.

            The broad way in which Guix manages the system
            configuration, and does so as a proper feature set it
            apart from other systems I've used, like Ansible and
            Puppet, where you attempt to converge some system to the
            desired state, and usually specify more about what you
            want, than what you don't, which can leave room for
            systems to become inconsistent in bad ways.

            I'm also enjoying not having to convince apt to untangle
            Debian systems that I've broken when trying to upgrade.
          </aside>
        </section>

        <section>
          <h2>Services</h2>

          <pre><code class="scheme">...

  (services (cons* (dhcp-client-service)
                   (service openssh-service-type
                            (openssh-configuration
                              (port-number 2222)))
                   %base-services)))</code></pre>


          <aside class="notes" data-markdown>
            One important part of GuixSD is the services.

            Guix packages are usable on other systems, however
            services are specific to GuixSD.

            They are similar though, in that they are both described
            through values in Guile.

            I won't go in to writing service definitions here, though
            it is something that I quite enjoy doing.

            There are quite a few examples in Guix at the moment, so
            you might be able to get a feel for them by looking at the
            documentation and the source code.

            Guix services can cooperate together by a process called
            service extension. For example, services that describe a
            daemon extend the root shepherd service, passing across
            the details of the service they want to provide.
          </aside>
        </section>

        <section data-background-color="white">
          <img class="stretch noborder"
               src="bare-bones-extension-graph.svg">
          <span class="caption">Extension graph</span>

          <aside class="notes" data-markdown>
            Here is the extension graph for the system definition I
            showed previously.

            Note all of the services extending the shepherd-root
            service.
          </aside>
        </section>

        <section data-background-color="white">
          <img class="stretch noborder"
               src="bare-bones-shepherd-graph.svg">
          <span class="caption">Shepherd graph</span>

          <aside class="notes" data-markdown>
            Mostly just because it's easy, here is the graph of the
            shepherd services from the system definition I showed
            previously.

            For both these graphs, there are neater layouts, but these
            were the best layouts I came up with for fitting on a
            slide.
          </aside>
        </section>

        <section>
          <h1>
            Extending Guix
          </h1>

          <aside class="notes" data-markdown>
            One of the areas where I think Guix really excels is
            extensibility.

            Because most of the functionality is defined through code,
            you're already in an environment where you have a lot of
            control.
          </aside>
        </section>

        <section>
          <h2>Writing a package definition</h2>

          <p>
            Importers available for: gnu, nix, pypi, cpan, hackage,
            stackage, elpa, gem, cran, crate, texlive and json.
          </p>

          <aside class="notes" data-markdown>
            If you want to use something, and can't find a existing
            package for it, you could look at writing one.

            Guix has definitions for around six and a half thousand
            packages, but if you are used to the packages from Debian
            for example, there will be some stuff missing.

            Guix contains several importers, which can use existing
            metadata from some source, to construct a package
            definition.

            Depending on the importer, and how complete the
            information was that it got from the relevant source, you
            might be able to build this package straight away, or it
            might need some tweaking.
          </aside>
        </section>

        <section>
          <h2>Hello package definition</h2>

          <small class="stretch"><pre>
            <code class="scheme">(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)
    (synopsis "Hello, GNU world: An example GNU package")
    (description
     "GNU Hello prints the message \"Hello, world!\" and then exits.  It
serves as an example of standard GNU coding practices.  As such, it supports
command-line arguments, multiple languages, and so on.")
    (home-page "https://www.gnu.org/software/hello/")
    (license gpl3+)))</code></pre></small>

          <aside class="notes" data-markdown>
            For some packages, like hello here, the package definition
            is quite simple.

            There are definitely packages in Guix where this is not
            the case.

            If there is not an importer available, or if the importer
            does a poor job, the other practical way of writing a
            package definition is to find something similar, and adapt
            it.
          </aside>
        </section>

        <section>
          <h2>Inheritance</h2>

          <small class="stretch"><pre><code class="scheme">(define-public ruby-2.3
  (package
    (inherit ruby)
    (version "2.3.5")
    (source
     (origin
       (method url-fetch)
       (uri (string-append "http://cache.ruby-lang.org/pub/ruby/"
                           (version-major+minor version)
                           "/ruby-" version ".tar.xz"))
       (sha256
        (base32
         "1npzcnq5kh0f9y88w5gj4v6ln8csr91361k3r43dmhlhn6mpsfkx"))
       (modules '((guix build utils)))
       (snippet `(begin
                   ;; Remove bundled libffi
                   (delete-file-recursively "ext/fiddle/libffi-3.2.1")
                   #t))))))</code></pre></small>

          <aside class="notes" data-markdown>
            Inheritance can come in really useful if you end up
            extending Guix.
            
            Because Guix uses values, mostly records in Guile to
            describe things. You can create new records by inheriting
            from a record, and just overriding some of the fields.

            This is used within Guix for package definitions that are
            similar, here for example, ruby, which is inherited from
            is the 2.4.2 release of ruby, so to define the package for
            the 2.3 version, you just inherit, and override the
            version and source.

            This type of inheritance can be really useful when making
            Guix packages suit your needs.
          </aside>
        </section>

        <section>
          <h2>G-expressions, a way of staging code</h2>

          <pre><code class="scheme">(define build-exp
  #~(begin
      (mkdir #$output)
      (chdir #$output)
      (symlink (string-append #$coreutils "/bin/ls")
               "list-files")))</code></pre>

          <aside class="notes" data-markdown>
            G-expressions could easily be a whole talk on there own,
            so I won't go in to two much detail here, only to say that
            if you start trying to implement services, or do
            interesting stuff extending Guix, you'll probably be
            leveraging G-expressions.

            There a way of staging code to run as a derivation. Here
            for example, this G-expression describes creating some
            output directory, and then creating a symlink to the ls
            binary in the coreutils package.

            G-expressions make it really easy to do complicated things
            with Guix, mostly by providing an easy way to handle the
            representation of things that can end up as store items.
          </aside>
        </section>

        <section>
          <h1>What is Guix?</h1>

          <span class="fragment">
            Standalone package definitions<br>+ bootstrap binaries
          </span><br><br>
          <span class="fragment">Package management tool + library</span><br><br>
          <span class="fragment">
            GNU+Linux distribution, with declarative<br>configuration for
            the system and services
          </span><br><br>
          <span class="fragment">
            <small>
            Build packages from source, offload build tasks to other
            machines, copy store items to other machines, graph
            packages and systems, inspect the size of store items,
            publish substitutes, run the garbage collector, generate
            package definitions from various sources, update package
            definitions for new releases, build raw or ISO disk
            images...
            </small>
          </span>

          <aside class="notes" data-markdown>
            Given all of this, the question "what is Guix?" isn't very
            easy to give a single answer to.

            (Next fragment)

            One aspect of Guix is the standalone package definitions,
            and the bootstrap binaries. Together providing a stable,
            controllable and inspectable set of software which you can
            use directly, and also use as a stable foundation to build
            upon.

            (Next fragment)

            Along with this, Guix has tooling to make use of the
            package definitions, providing a number of different ways
            in which to use them.

            From the guix package command, to manage persistent
            profiles, to the guix environment command to create more
            temporary profiles and development environments, to the
            guix pack command, which allows you to take packages and
            pack them up in different ways, currently a tarball and
            Docker image also known as the Open Container Initiative
            image format.

            Even more functionality and flexibility is available if
            you need it, by directly using Guix as a library.

            (Next fragment)

            On top of all of this, Guix provides and brings together
            the software and tooling you need to setup a GNU+Linux
            distribution, a.k.a GuixSD, the Guix system distribution.

            The state of the system can be specified in a declarative
            way, from the user accounts, to the file systems, to the
            configuration for many services like PostgreSQL, OpenSSH,
            MongoDB, nginx, Dovecot and many more.

            Using the same approaches as for packages and profiles,
            this offers roll backs for the system profile, not only
            switching back to a previous version of Linux if
            applicable, but other parts of the system as well.

            To complement this, Guix includes the tooling for systems
            to generate disk images, system containers and virtual
            machines, all from a operating system definition.

            (Next fragment)

            And then come all the smaller features, that I think still
            make a big difference.

            Building packages from source is seemless, just change the
            package definition, and then use it. If you need to change
            a dependency of the package you care about, or a
            dependency of a dependency of a package you care about,
            then its no different.

            Build tasks can be offloaded to other machines. You can
            generate graphs for packages, showing the inputs, and
            their inputs, and so on.

            The guix size command will show you the references of a
            store item, along with their size.

            The guix publish command and service can be used to
            publish binary substitutes, for use on other machines. The
            guix gc command invokes the garbage collector allows you
            to remove unused items from the store, freeing up disk
            space.

            The guix import command can generate package definitions
            from various sources like the Python package index,
            Rubygems.org, CPAN, Hackage, Stackage, Elpa and more.

            The guix refresh command can for some packages update the
            package definitions, by checking for new releases.

            And... there is probably even more things that I've
            missed, and I haven't even covered any of the tooling that
            people have built that uses or enhances Guix.
          </aside>
        </section>

        <section>
          <h2>Use Guix!</h2>

          <p>
            Install Guix within an existing system.
          </p>

          <p>
            Install GuixSD, a distribution of GNU+Linux.
          </p>

          <aside class="notes" data-markdown>
            If you are going to directly benefit from all of this,
            then there are a few different ways of using Guix.

            You can use it within a existing system. The Linux and
            Hurd kernels are supported, and Guix has been ported to
            the x86 64, i686 and armhf architectures.

            Due to the way Guix works, it's very isolated from the
            system its installed on. By default, just requiring two
            directories, /gnu and /var/guix and the build daemon to be
            running.

            With Guix installed within an existing system, you can
            create system containers, virtual machines, but to take
            full advantage of features such as the declarative system
            configuration, you'll need to install GuixSD.
          </aside>
        </section>

        <section>
          <h3>Talk to others on</h3>
          <h2>#guix on freenode</h2>

          <p>
            For the manual, mailing lists, papers, blog posts and
            talks, go to
            <a href="https://gnu.org/s/guix/help">
              https://gnu.org/s/guix/help
            </a>
          </p>

          <aside class="notes" data-markdown>
            If you'd like to talk to others, there is an active IRC
            channel, #guix on Freenode.

            I'm in there, my nick is cbaines.

            From the website, you can find a online version of the
            manual, and details on the mailing lists.
          </alias>
        </section>
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