GNU Guix Cookbook

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GNU Guix Cookbook

This document presents tutorials and detailed examples for GNU Guix, a functional package management tool written for the GNU system. Please see GNU Guix reference manual for details about the system, its API, and related concepts.

If you would like to translate this document in your native language, consider joining the Translation Project.


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1 Scheme tutorials

GNU Guix is written in the general purpose programming language Scheme, and many of its features can be accessed and manipulated programmatically. You can use Scheme to generate package definitions, to modify them, to build them, to deploy whole operating systems, etc.

Knowing the basics of how to program in Scheme will unlock many of the advanced features Guix provides — and you don’t even need to be an experienced programmer to use them!

Let’s get started!


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1.1 A Scheme Crash Course

Guix uses the Guile implementation of Scheme. To start playing with the language, install it with guix install guile and start a REPL by running guile from the command line.

Alternatively you can also run guix environment --ad-hoc guile -- guile if you’d rather not have Guile installed in your user profile.

In the following examples, lines show what you would type at the REPL; lines starting with “⇒” show evaluation results, while lines starting with “-|” show things that get printed. See Using Guile Interactively in GNU Guile Reference Manual), for more details on the REPL.

For a more detailed introduction, check out Scheme at a Glance, by Steve Litt.

One of the reference Scheme books is the seminal “Structure and Interpretation of Computer Programs”, by Harold Abelson and Gerald Jay Sussman, with Julie Sussman. You’ll find a free copy online, together with videos of the lectures by the authors. The book is available in Texinfo format as the sicp Guix package. Go ahead, run guix install sicp and start reading with info sicp (see Structure and Interpretation of Computer Programs). An unofficial ebook is also available.

You’ll find more books, tutorials and other resources at https://schemers.org/.


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2 Packaging

This chapter is dedicated to teaching you how to add packages to the collection of packages that come with GNU Guix. This involves writing package definitions in Guile Scheme, organizing them in package modules, and building them.


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2.1 Packaging Tutorial

GNU Guix stands out as the hackable package manager, mostly because it uses GNU Guile, a powerful high-level programming language, one of the Scheme dialects from the Lisp family.

Package definitions are also written in Scheme, which empowers Guix in some very unique ways, unlike most other package managers that use shell scripts or simple languages.

The following tutorial covers all the basics around package creation with Guix. It does not assume much knowledge of the Guix system nor of the Lisp language. The reader is only expected to be familiar with the command line and to have some basic programming knowledge.


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2.1.1 A “Hello World” package

The “Defining Packages” section of the manual introduces the basics of Guix packaging (see Defining Packages in GNU Guix Reference Manual). In the following section, we will partly go over those basics again.

GNU Hello is a dummy project that serves as an idiomatic example for packaging. It uses the GNU build system (./configure && make && make install). Guix already provides a package definition which is a perfect example to start with. You can look up its declaration with guix edit hello from the command line. Let’s see how it looks:

(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+)))

As you can see, most of it is rather straightforward. But let’s review the fields together:

name

The project name. Using Scheme conventions, we prefer to keep it lower case, without underscore and using dash-separated words.

source

This field contains a description of the source code origin. The origin record contains these fields:

  1. The method, here url-fetch to download via HTTP/FTP, but other methods exist, such as git-fetch for Git repositories.
  2. The URI, which is typically some https:// location for url-fetch. Here the special ‘mirror://gnu‘ refers to a set of well known locations, all of which can be used by Guix to fetch the source, should some of them fail.
  3. The sha256 checksum of the requested file. This is essential to ensure the source is not corrupted. Note that Guix works with base32 strings, hence the call to the base32 function.
build-system

This is where the power of abstraction provided by the Scheme language really shines: in this case, the gnu-build-system abstracts away the famous ./configure && make && make install shell invocations. Other build systems include the trivial-build-system which does not do anything and requires from the packager to program all the build steps, the python-build-system, the emacs-build-system, and many more (see Build Systems in GNU Guix Reference Manual).

synopsis

It should be a concise summary of what the package does. For many packages a tagline from the project’s home page can be used as the synopsis.

description

Same as for the synopsis, it’s fine to re-use the project description from the homepage. Note that Guix uses Texinfo syntax.

home-page

Use HTTPS if available.

license

See guix/licenses.scm in the project source for a full list of available licenses.

Time to build our first package! Nothing fancy here for now: we will stick to a dummy my-hello, a copy of the above declaration.

As with the ritualistic “Hello World” taught with most programming languages, this will possibly be the most “manual” approach. We will work out an ideal setup later; for now we will go the simplest route.

Save the following to a file my-hello.scm.

(use-modules (guix packages)
             (guix download)
             (guix build-system gnu)
             (guix licenses))

(package
  (name "my-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, Guix world: An example custom Guix 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+))

We will explain the extra code in a moment.

Feel free to play with the different values of the various fields. If you change the source, you’ll need to update the checksum. Indeed, Guix refuses to build anything if the given checksum does not match the computed checksum of the source code. To obtain the correct checksum of the package declaration, we need to download the source, compute the sha256 checksum and convert it to base32.

Thankfully, Guix can automate this task for us; all we need is to provide the URI:

$ guix download mirror://gnu/hello/hello-2.10.tar.gz

Starting download of /tmp/guix-file.JLYgL7
From https://ftpmirror.gnu.org/gnu/hello/hello-2.10.tar.gz...
following redirection to `https://mirror.ibcp.fr/pub/gnu/hello/hello-2.10.tar.gz'...
 …10.tar.gz  709KiB                                 2.5MiB/s 00:00 [##################] 100.0%
/gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz
0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i

In this specific case the output tells us which mirror was chosen. If the result of the above command is not the same as in the above snippet, update your my-hello declaration accordingly.

Note that GNU package tarballs come with an OpenPGP signature, so you should definitely check the signature of this tarball with ‘gpg‘ to authenticate it before going further:

$ guix download mirror://gnu/hello/hello-2.10.tar.gz.sig

Starting download of /tmp/guix-file.03tFfb
From https://ftpmirror.gnu.org/gnu/hello/hello-2.10.tar.gz.sig...
following redirection to `https://ftp.igh.cnrs.fr/pub/gnu/hello/hello-2.10.tar.gz.sig'...
 ….tar.gz.sig  819B                                                                                                                       1.2MiB/s 00:00 [##################] 100.0%
/gnu/store/rzs8wba9ka7grrmgcpfyxvs58mly0sx6-hello-2.10.tar.gz.sig
0q0v86n3y38z17rl146gdakw9xc4mcscpk8dscs412j22glrv9jf
$ gpg --verify /gnu/store/rzs8wba9ka7grrmgcpfyxvs58mly0sx6-hello-2.10.tar.gz.sig /gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz
gpg: Signature made Sun 16 Nov 2014 01:08:37 PM CET
gpg:                using RSA key A9553245FDE9B739
gpg: Good signature from "Sami Kerola <kerolasa@iki.fi>" [unknown]
gpg:                 aka "Sami Kerola (http://www.iki.fi/kerolasa/) <kerolasa@iki.fi>" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: 8ED3 96E3 7E38 D471 A005  30D3 A955 3245 FDE9 B739

You can then happily run

$ guix package --install-from-file=my-hello.scm

You should now have my-hello in your profile!

$ guix package --list-installed=my-hello
my-hello	2.10	out
/gnu/store/f1db2mfm8syb8qvc357c53slbvf1g9m9-my-hello-2.10

We’ve gone as far as we could without any knowledge of Scheme. Before moving on to more complex packages, now is the right time to brush up on your Scheme knowledge. see A Scheme Crash Course to get up to speed.


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2.1.2 Setup

In the rest of this chapter we will rely on some basic Scheme programming knowledge. Now let’s detail the different possible setups for working on Guix packages.

There are several ways to set up a Guix packaging environment.

We recommend you work directly on the Guix source checkout since it makes it easier for everyone to contribute to the project.

But first, let’s look at other possibilities.


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2.1.2.1 Local file

This is what we previously did with ‘my-hello’. With the Scheme basics we’ve covered, we are now able to explain the leading chunks. As stated in guix package --help:

  -f, --install-from-file=FILE
                         install the package that the code within FILE
                         evaluates to

Thus the last expression must return a package, which is the case in our earlier example.

The use-modules expression tells which of the modules we need in the file. Modules are a collection of values and procedures. They are commonly called “libraries” or “packages” in other programming languages.


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2.1.2.2 ‘GUIX_PACKAGE_PATH

Note: Starting from Guix 0.16, the more flexible Guix channels are the preferred way and supersede ‘GUIX_PACKAGE_PATH’. See next section.

It can be tedious to specify the file from the command line instead of simply calling guix package --install my-hello as you would do with the official packages.

Guix makes it possible to streamline the process by adding as many “package declaration directories” as you want.

Create a directory, say ‘~./guix-packages’ and add it to the ‘GUIX_PACKAGE_PATH’ environment variable:

$ mkdir ~/guix-packages
$ export GUIX_PACKAGE_PATH=~/guix-packages

To add several directories, separate them with a colon (:).

Our previous ‘my-hello’ needs some adjustments though:

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

(define-public my-hello
  (package
    (name "my-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, Guix world: An example custom Guix 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+)))

Note that we have assigned the package value to an exported variable name with define-public. This is effectively assigning the package to the my-hello variable so that it can be referenced, among other as dependency of other packages.

If you use guix package --install-from-file=my-hello.scm on the above file, it will fail because the last expression, define-public, does not return a package. If you want to use define-public in this use-case nonetheless, make sure the file ends with an evaluation of my-hello:

; ...
(define-public my-hello
  ; ...
  )

my-hello

This last example is not very typical.

Now ‘my-hello’ should be part of the package collection like all other official packages. You can verify this with:

$ guix package --show=my-hello

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2.1.2.3 Guix channels

Guix 0.16 features channels, which is very similar to ‘GUIX_PACKAGE_PATH’ but provides better integration and provenance tracking. Channels are not necessarily local, they can be maintained as a public Git repository for instance. Of course, several channels can be used at the same time.

See Channels in GNU Guix Reference Manual for setup details.


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2.1.2.4 Direct checkout hacking

Working directly on the Guix project is recommended: it reduces the friction when the time comes to submit your changes upstream to let the community benefit from your hard work!

Unlike most software distributions, the Guix repository holds in one place both the tooling (including the package manager) and the package definitions. This choice was made so that it would give developers the flexibility to modify the API without breakage by updating all packages at the same time. This reduces development inertia.

Check out the official Git repository:

$ git clone https://git.savannah.gnu.org/git/guix.git

In the rest of this article, we use ‘$GUIX_CHECKOUT’ to refer to the location of the checkout.

Follow the instructions in the manual (see Contributing in GNU Guix Reference Manual) to set up the repository environment.

Once ready, you should be able to use the package definitions from the repository environment.

Feel free to edit package definitions found in ‘$GUIX_CHECKOUT/gnu/packages’.

The ‘$GUIX_CHECKOUT/pre-inst-env’ script lets you use ‘guix’ over the package collection of the repository (see Running Guix Before It Is Installed in GNU Guix Reference Manual).

Guix strives at maintaining a high packaging standard; when contributing to the Guix project, remember to

Once you are happy with the result, you are welcome to send your contribution to make it part of Guix. This process is also detailed in the manual. (see Contributing in GNU Guix Reference Manual)

It’s a community effort so the more join in, the better Guix becomes!


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2.1.3 Extended example

The above “Hello World” example is as simple as it goes. Packages can be more complex than that and Guix can handle more advanced scenarios. Let’s look at another, more sophisticated package (slightly modified from the source):

(define-module (gnu packages version-control)
  #:use-module ((guix licenses) #:prefix license:)
  #:use-module (guix utils)
  #:use-module (guix packages)
  #:use-module (guix git-download)
  #:use-module (guix build-system cmake)
  #:use-module (gnu packages ssh)
  #:use-module (gnu packages web)
  #:use-module (gnu packages pkg-config)
  #:use-module (gnu packages python)
  #:use-module (gnu packages compression)
  #:use-module (gnu packages tls))

(define-public my-libgit2
  (let ((commit "e98d0a37c93574d2c6107bf7f31140b548c6a7bf")
        (revision "1"))
    (package
      (name "my-libgit2")
      (version (git-version "0.26.6" revision commit))
      (source (origin
                (method git-fetch)
                (uri (git-reference
                      (url "https://github.com/libgit2/libgit2/")
                      (commit commit)))
                (file-name (git-file-name name version))
                (sha256
                 (base32
                  "17pjvprmdrx4h6bb1hhc98w9qi6ki7yl57f090n9kbhswxqfs7s3"))
                (patches (search-patches "libgit2-mtime-0.patch"))
                (modules '((guix build utils)))
                (snippet '(begin
                            ;; Remove bundled software.
                            (delete-file-recursively "deps")
                            #t))))
      (build-system cmake-build-system)
      (outputs '("out" "debug"))
      (arguments
       `(#:tests? #t                            ; Run the test suite (this is the default)
         #:configure-flags '("-DUSE_SHA1DC=ON") ; SHA-1 collision detection
         #:phases
         (modify-phases %standard-phases
           (add-after 'unpack 'fix-hardcoded-paths
             (lambda _
               (substitute* "tests/repo/init.c"
                 (("#!/bin/sh") (string-append "#!" (which "sh"))))
               (substitute* "tests/clar/fs.h"
                 (("/bin/cp") (which "cp"))
                 (("/bin/rm") (which "rm")))
               #t))
           ;; Run checks more verbosely.
           (replace 'check
             (lambda _ (invoke "./libgit2_clar" "-v" "-Q")))
           (add-after 'unpack 'make-files-writable-for-tests
               (lambda _ (for-each make-file-writable (find-files "." ".*")))))))
      (inputs
       `(("libssh2" ,libssh2)
         ("http-parser" ,http-parser)
         ("python" ,python-wrapper)))
      (native-inputs
       `(("pkg-config" ,pkg-config)))
      (propagated-inputs
       ;; These two libraries are in 'Requires.private' in libgit2.pc.
       `(("openssl" ,openssl)
         ("zlib" ,zlib)))
      (home-page "https://libgit2.github.com/")
      (synopsis "Library providing Git core methods")
      (description
       "Libgit2 is a portable, pure C implementation of the Git core methods
provided as a re-entrant linkable library with a solid API, allowing you to
write native speed custom Git applications in any language with bindings.")
      ;; GPLv2 with linking exception
      (license license:gpl2))))

(In those cases were you only want to tweak a few fields from a package definition, you should rely on inheritance instead of copy-pasting everything. See below.)

Let’s discuss those fields in depth.

2.1.3.1 git-fetch method

Unlike the url-fetch method, git-fetch expects a git-reference which takes a Git repository and a commit. The commit can be any Git reference such as tags, so if the version is tagged, then it can be used directly. Sometimes the tag is prefixed with a v, in which case you’d use (commit (string-append "v" version)).

To ensure that the source code from the Git repository is stored in a unique directory with a readable name we use (file-name (git-file-name name version)).

Note that there is also a git-version procedure that can be used to derive the version when packaging programs for a specific commit.

2.1.3.2 Snippets

Snippets are quoted (i.e. non-evaluated) Scheme code that are a means of patching the source. They are a Guix-y alternative to the traditional ‘.patch’ files. Because of the quote, the code in only evaluated when passed to the Guix daemon for building. There can be as many snippets as needed.

Snippets might need additional Guile modules which can be imported from the modules field.

2.1.3.3 Inputs

First, a syntactic comment: See the quasi-quote / comma syntax?

    (native-inputs
     `(("pkg-config" ,pkg-config)))

is equivalent to

    (native-inputs
     (list (list "pkg-config" pkg-config)))

You’ll mostly see the former because it’s shorter.

There are 3 different input types. In short:

native-inputs

Required for building but not runtime – installing a package through a substitute won’t install these inputs.

inputs

Installed in the store but not in the profile, as well as being present at build time.

propagated-inputs

Installed in the store and in the profile, as well as being present at build time.

See Package Reference in GNU Guix Reference Manual for more details.

The distinction between the various inputs is important: if a dependency can be handled as an input instead of a propagated input, it should be done so, or else it “pollutes” the user profile for no good reason.

For instance, a user installing a graphical program that depends on a command line tool might only be interested in the graphical part, so there is no need to force the command line tool into the user profile. The dependency is a concern to the package, not to the user. Inputs make it possible to handle dependencies without bugging the user by adding undesired executable files (or libraries) to their profile.

Same goes for native-inputs: once the program is installed, build-time dependencies can be safely garbage-collected. It also matters when a substitute is available, in which case only the inputs and propagated inputs will be fetched: the native inputs are not required to install a package from a substitute.

2.1.3.4 Outputs

Just like how a package can have multiple inputs, it can also produce multiple outputs.

Each output corresponds to a separate directory in the store.

The user can choose which output to install; this is useful to save space or to avoid polluting the user profile with unwanted executables or libraries.

Output separation is optional. When the outputs field is left out, the default and only output (the complete package) is referred to as "out".

Typical separate output names include debug and doc.

It’s advised to separate outputs only when you’ve shown it’s worth it: if the output size is significant (compare with guix size) or in case the package is modular.

2.1.3.5 Build system arguments

The arguments is a keyword-value list used to configure the build process.

The simplest argument #:tests? can be used to disable the test suite when building the package. This is mostly useful when the package does not feature any test suite. It’s strongly recommended to keep the test suite on if there is one.

Another common argument is :make-flags, which specifies a list of flags to append when running make, as you would from the command line. For instance, the following flags

#:make-flags (list (string-append "prefix=" (assoc-ref %outputs "out"))
                   "CC=gcc")

translate into

$ make CC=gcc prefix=/gnu/store/...-<out>

This sets the C compiler to gcc and the prefix variable (the installation directory in Make parlance) to (assoc-ref %outputs "out"), which is a build-stage global variable pointing to the destination directory in the store (something like ‘/gnu/store/...-my-libgit2-20180408’).

Similarly, it’s possible to set the configure flags:

#:configure-flags '("-DUSE_SHA1DC=ON")

The %build-inputs variable is also generated in scope. It’s an association table that maps the input names to their store directories.

The phases keyword lists the sequential steps of the build system. Typically phases include unpack, configure, build, install and check. To know more about those phases, you need to work out the appropriate build system definition in ‘$GUIX_CHECKOUT/guix/build/gnu-build-system.scm’:

(define %standard-phases
  ;; Standard build phases, as a list of symbol/procedure pairs.
  (let-syntax ((phases (syntax-rules ()
                         ((_ p ...) `((p . ,p) ...)))))
    (phases set-SOURCE-DATE-EPOCH set-paths install-locale unpack
            bootstrap
            patch-usr-bin-file
            patch-source-shebangs configure patch-generated-file-shebangs
            build check install
            patch-shebangs strip
            validate-runpath
            validate-documentation-location
            delete-info-dir-file
            patch-dot-desktop-files
            install-license-files
            reset-gzip-timestamps
            compress-documentation)))

Or from the REPL:

(add-to-load-path "/path/to/guix/checkout")
,use (guix build gnu-build-system)
(map first %standard-phases)
 (set-SOURCE-DATE-EPOCH set-paths install-locale unpack bootstrap patch-usr-bin-file patch-source-shebangs configure patch-generated-file-shebangs build check install patch-shebangs strip validate-runpath validate-documentation-location delete-info-dir-file patch-dot-desktop-files install-license-files reset-gzip-timestamps compress-documentation)

If you want to know more about what happens during those phases, consult the associated procedures.

For instance, as of this writing the definition of unpack for the GNU build system is

(define* (unpack #:key source #:allow-other-keys)
  "Unpack SOURCE in the working directory, and change directory within the
source.  When SOURCE is a directory, copy it in a sub-directory of the current
working directory."
  (if (file-is-directory? source)
      (begin
        (mkdir "source")
        (chdir "source")

        ;; Preserve timestamps (set to the Epoch) on the copied tree so that
        ;; things work deterministically.
        (copy-recursively source "."
                          #:keep-mtime? #t))
      (begin
        (if (string-suffix? ".zip" source)
            (invoke "unzip" source)
            (invoke "tar" "xvf" source))
        (chdir (first-subdirectory "."))))
  #t)

Note the chdir call: it changes the working directory to where the source was unpacked. Thus every phase following the unpack will use the source as a working directory, which is why we can directly work on the source files. That is to say, unless a later phase changes the working directory to something else.

We modify the list of %standard-phases of the build system with the modify-phases macro as per the list of specified modifications, which may have the following forms:

The PROCEDURE supports the keyword arguments inputs and outputs. Each input (whether native, propagated or not) and output directory is referenced by their name in those variables. Thus (assoc-ref outputs "out") is the store directory of the main output of the package. A phase procedure may look like this:

(lambda* (#:key inputs outputs #:allow-other-keys)
  (let (((bash-directory (assoc-ref inputs "bash"))
         (output-directory (assoc-ref outputs "out"))
         (doc-directory (assoc-ref outputs "doc"))
  ; ...
  #t)

The procedure must return #t on success. It’s brittle to rely on the return value of the last expression used to tweak the phase because there is no guarantee it would be a #t. Hence the trailing #t to ensure the right value is returned on success.

2.1.3.6 Code staging

The astute reader may have noticed the quasi-quote and comma syntax in the argument field. Indeed, the build code in the package declaration should not be evaluated on the client side, but only when passed to the Guix daemon. This mechanism of passing code around two running processes is called code staging.

2.1.3.7 Utility functions

When customizing phases, we often need to write code that mimics the equivalent system invocations (make, mkdir, cp, etc.) commonly used during regular “Unix-style” installations.

Some like chmod are native to Guile. See Guile reference manual for a complete list.

Guix provides additional helper functions which prove especially handy in the context of package management.

Some of those functions can be found in ‘$GUIX_CHECKOUT/guix/guix/build/utils.scm’. Most of them mirror the behaviour of the traditional Unix system commands:

which

Like the ‘which’ system command.

find-files

Akin to the ‘find’ system command.

mkdir-p

Like ‘mkdir -p’, which creates all parents as needed.

install-file

Similar to ‘install’ when installing a file to a (possibly non-existing) directory. Guile has copy-file which works like ‘cp’.

copy-recursively

Like ‘cp -r’.

delete-file-recursively

Like ‘rm -rf’.

invoke

Run an executable. This should be used instead of system*.

with-directory-excursion

Run the body in a different working directory, then restore the previous working directory.

substitute*

A “sed-like” function.

2.1.3.8 Module prefix

The license in our last example needs a prefix: this is because of how the license module was imported in the package, as #:use-module ((guix licenses) #:prefix license:). The Guile module import mechanism (see Using Guile Modules in Guile reference manual) gives the user full control over namespacing: this is needed to avoid clashes between, say, the ‘zlib’ variable from ‘licenses.scm’ (a license value) and the ‘zlib’ variable from ‘compression.scm’ (a package value).


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2.1.4 Other build systems

What we’ve seen so far covers the majority of packages using a build system other than the trivial-build-system. The latter does not automate anything and leaves you to build everything manually. This can be more demanding and we won’t cover it here for now, but thankfully it is rarely necessary to fall back on this system.

For the other build systems, such as ASDF, Emacs, Perl, Ruby and many more, the process is very similar to the GNU build system except for a few specialized arguments.

See Build Systems in GNU Guix Reference Manual, for more information on build systems, or check the source code in the ‘$GUIX_CHECKOUT/guix/build’ and ‘$GUIX_CHECKOUT/guix/build-system’ directories.


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2.1.5 Programmable and automated package definition

We can’t repeat it enough: having a full-fledged programming language at hand empowers us in ways that reach far beyond traditional package management.

Let’s illustrate this with some awesome features of Guix!


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2.1.5.1 Recursive importers

You might find some build systems good enough that there is little to do at all to write a package, to the point that it becomes repetitive and tedious after a while. A raison d’être of computers is to replace human beings at those boring tasks. So let’s tell Guix to do this for us and create the package definition of an R package from CRAN (the output is trimmed for conciseness):

$ guix import cran --recursive walrus

(define-public r-mc2d
    ; ...
    (license gpl2+)))

(define-public r-jmvcore
    ; ...
    (license gpl2+)))

(define-public r-wrs2
    ; ...
    (license gpl3)))

(define-public r-walrus
  (package
    (name "r-walrus")
    (version "1.0.3")
    (source
      (origin
        (method url-fetch)
        (uri (cran-uri "walrus" version))
        (sha256
          (base32
            "1nk2glcvy4hyksl5ipq2mz8jy4fss90hx6cq98m3w96kzjni6jjj"))))
    (build-system r-build-system)
    (propagated-inputs
      `(("r-ggplot2" ,r-ggplot2)
        ("r-jmvcore" ,r-jmvcore)
        ("r-r6" ,r-r6)
        ("r-wrs2" ,r-wrs2)))
    (home-page "https://github.com/jamovi/walrus")
    (synopsis "Robust Statistical Methods")
    (description
      "This package provides a toolbox of common robust statistical
tests, including robust descriptives, robust t-tests, and robust ANOVA.
It is also available as a module for 'jamovi' (see
<https://www.jamovi.org> for more information).  Walrus is based on the
WRS2 package by Patrick Mair, which is in turn based on the scripts and
work of Rand Wilcox.  These analyses are described in depth in the book
'Introduction to Robust Estimation & Hypothesis Testing'.")
    (license gpl3)))

The recursive importer won’t import packages for which Guix already has package definitions, except for the very first.

Not all applications can be packaged this way, only those relying on a select number of supported systems. Read about the full list of importers in the guix import section of the manual (see Invoking guix import in GNU Guix Reference Manual).


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2.1.5.2 Automatic update

Guix can be smart enough to check for updates on systems it knows. It can report outdated package definitions with

$ guix refresh hello

In most cases, updating a package to a newer version requires little more than changing the version number and the checksum. Guix can do that automatically as well:

$ guix refresh hello --update

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2.1.5.3 Inheritance

If you’ve started browsing the existing package definitions, you might have noticed that a significant number of them have a inherit field:

(define-public adwaita-icon-theme
  (package (inherit gnome-icon-theme)
    (name "adwaita-icon-theme")
    (version "3.26.1")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnome/sources/" name "/"
                                  (version-major+minor version) "/"
                                  name "-" version ".tar.xz"))
              (sha256
               (base32
                "17fpahgh5dyckgz7rwqvzgnhx53cx9kr2xw0szprc6bnqy977fi8"))))
    (native-inputs
     `(("gtk-encode-symbolic-svg" ,gtk+ "bin")))))

All unspecified fields are inherited from the parent package. This is very convenient to create alternative packages, for instance with different source, version or compilation options.


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2.1.6 Getting help

Sadly, some applications can be tough to package. Sometimes they need a patch to work with the non-standard filesystem hierarchy enforced by the store. Sometimes the tests won’t run properly. (They can be skipped but this is not recommended.) Other times the resulting package won’t be reproducible.

Should you be stuck, unable to figure out how to fix any sort of packaging issue, don’t hesitate to ask the community for help.

See the Guix homepage for information on the mailing lists, IRC, etc.


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2.1.7 Conclusion

This tutorial was a showcase of the sophisticated package management that Guix boasts. At this point we have mostly restricted this introduction to the gnu-build-system which is a core abstraction layer on which more advanced abstractions are based.

Where do we go from here? Next we ought to dissect the innards of the build system by removing all abstractions, using the trivial-build-system: this should give us a thorough understanding of the process before investigating some more advanced packaging techniques and edge cases.

Other features worth exploring are the interactive editing and debugging capabilities of Guix provided by the Guile REPL.

Those fancy features are completely optional and can wait; now is a good time to take a well-deserved break. With what we’ve introduced here you should be well armed to package lots of programs. You can get started right away and hopefully we will see your contributions soon!


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2.1.8 References


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3 System Configuration

Guix offers a flexible language for declaratively configuring your Guix System. This flexibility can at times be overwhelming. The purpose of this chapter is to demonstrate some advanced configuration concepts.

see System Configuration in GNU Guix Reference Manual for a complete reference.


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3.1 Customizing the Kernel

Guix is, at its core, a source based distribution with substitutes (see Substitutes in GNU Guix Reference Manual), and as such building packages from their source code is an expected part of regular package installations and upgrades. Given this starting point, it makes sense that efforts are made to reduce the amount of time spent compiling packages, and recent changes and upgrades to the building and distribution of substitutes continues to be a topic of discussion within Guix.

The kernel, while not requiring an overabundance of RAM to build, does take a rather long time on an average machine. The official kernel configuration, as is the case with many GNU/Linux distributions, errs on the side of inclusiveness, and this is really what causes the build to take such a long time when the kernel is built from source.

The Linux kernel, however, can also just be described as a regular old package, and as such can be customized just like any other package. The procedure is a little bit different, although this is primarily due to the nature of how the package definition is written.

The linux-libre kernel package definition is actually a procedure which creates a package.

(define* (make-linux-libre version hash supported-systems
                           #:key
                           ;; A function that takes an arch and a variant.
                           ;; See kernel-config for an example.
                           (extra-version #f)
                           (configuration-file #f)
                           (defconfig "defconfig")
                           (extra-options %default-extra-linux-options)
                           (patches (list %boot-logo-patch)))
  ...)

The current linux-libre package is for the 5.1.x series, and is declared like this:

(define-public linux-libre
  (make-linux-libre %linux-libre-version
                    %linux-libre-hash
                    '("x86_64-linux" "i686-linux" "armhf-linux" "aarch64-linux")
                    #:patches %linux-libre-5.1-patches
                    #:configuration-file kernel-config))

Any keys which are not assigned values inherit their default value from the make-linux-libre definition. When comparing the two snippets above, you may notice that the code comment in the first doesn’t actually refer to the #:extra-version keyword; it is actually for #:configuration-file. Because of this, it is not actually easy to include a custom kernel configuration from the definition, but don’t worry, there are other ways to work with what we do have.

There are two ways to create a kernel with a custom kernel configuration. The first is to provide a standard .config file during the build process by including an actual .config file as a native input to our custom kernel. The following is a snippet from the custom 'configure phase of the make-linux-libre package definition:

(let ((build  (assoc-ref %standard-phases 'build))
      (config (assoc-ref (or native-inputs inputs) "kconfig")))

  ;; Use a custom kernel configuration file or a default
  ;; configuration file.
  (if config
      (begin
        (copy-file config ".config")
        (chmod ".config" #o666))
      (invoke "make" ,defconfig))

Below is a sample kernel package. The linux-libre package is nothing special and can be inherited from and have its fields overridden like any other package:

(define-public linux-libre/E2140
  (package
    (inherit linux-libre)
    (native-inputs
     `(("kconfig" ,(local-file "E2140.config"))
      ,@(alist-delete "kconfig"
                      (package-native-inputs linux-libre))))))

In the same directory as the file defining linux-libre-E2140 is a file named E2140.config, which is an actual kernel configuration file. The defconfig keyword of make-linux-libre is left blank here, so the only kernel configuration in the package is the one which was included in the native-inputs field.

The second way to create a custom kernel is to pass a new value to the extra-options keyword of the make-linux-libre procedure. The extra-options keyword works with another function defined right below it:

(define %default-extra-linux-options
  `(;; https://lists.gnu.org/archive/html/guix-devel/2014-04/msg00039.html
   ("CONFIG_DEVPTS_MULTIPLE_INSTANCES" . #t)
   ;; Modules required for initrd:
   ("CONFIG_NET_9P" . m)
   ("CONFIG_NET_9P_VIRTIO" . m)
   ("CONFIG_VIRTIO_BLK" . m)
   ("CONFIG_VIRTIO_NET" . m)
   ("CONFIG_VIRTIO_PCI" . m)
   ("CONFIG_VIRTIO_BALLOON" . m)
   ("CONFIG_VIRTIO_MMIO" . m)
   ("CONFIG_FUSE_FS" . m)
   ("CONFIG_CIFS" . m)
   ("CONFIG_9P_FS" . m)))

(define (config->string options)
  (string-join (map (match-lambda
                      ((option . 'm)
                       (string-append option "=m"))
                      ((option . #t)
                       (string-append option "=y"))
                      ((option . #f)
                       (string-append option "=n")))
                    options)
               "\n"))

And in the custom configure script from the ‘make-linux-libre‘ package:

;; Appending works even when the option wasn't in the
;; file.  The last one prevails if duplicated.
(let ((port (open-file ".config" "a"))
      (extra-configuration ,(config->string extra-options)))
  (display extra-configuration port)
  (close-port port))

(invoke "make" "oldconfig"))))

So by not providing a configuration-file the .config starts blank, and then we write into it the collection of flags that we want. Here’s another custom kernel:

(define %macbook41-full-config
  (append %macbook41-config-options
          %filesystems
          %efi-support
          %emulation
          (@@ (gnu packages linux) %default-extra-linux-options)))

(define-public linux-libre-macbook41
  ;; XXX: Access the internal 'make-linux-libre' procedure, which is
  ;; private and unexported, and is liable to change in the future.
  ((@@ (gnu packages linux) make-linux-libre) (@@ (gnu packages linux) %linux-libre-version)
                      (@@ (gnu packages linux) %linux-libre-hash)
                      '("x86_64-linux")
                      #:extra-version "macbook41"
                      #:patches (@@ (gnu packages linux) %linux-libre-5.1-patches)
                      #:extra-options %macbook41-config-options))

In the above example %filesystems is a collection of flags enabling different filesystem support, %efi-support enables EFI support and %emulation enables a x86_64-linux machine to act in 32-bit mode also. %default-extra-linux-options are the ones quoted above, which had to be added in since they were replaced in the extra-options keyword.

This all sounds like it should be doable, but how does one even know which modules are required for a particular system? Two places that can be helpful in trying to answer this question is the Gentoo Handbook and the documentation from the kernel itself. From the kernel documentation, it seems that make localmodconfig is the command we want.

In order to actually run make localmodconfig we first need to get and unpack the kernel source code:

tar xf $(guix build linux-libre --source)

Once inside the directory containing the source code run touch .config to create an initial, empty .config to start with. make localmodconfig works by seeing what you already have in .config and letting you know what you’re missing. If the file is blank then you’re missing everything. The next step is to run:

guix environment linux-libre -- make localmodconfig

and note the output. Do note that the .config file is still empty. The output generally contains two types of warnings. The first start with "WARNING" and can actually be ignored in our case. The second read:

module pcspkr did not have configs CONFIG_INPUT_PCSPKR

For each of these lines, copy the CONFIG_XXXX_XXXX portion into the .config in the directory, and append =m, so in the end it looks like this:

CONFIG_INPUT_PCSPKR=m
CONFIG_VIRTIO=m

After copying all the configuration options, run make localmodconfig again to make sure that you don’t have any output starting with “module”. After all of these machine specific modules there are a couple more left that are also needed. CONFIG_MODULES is necessary so that you can build and load modules separately and not have everything built into the kernel. CONFIG_BLK_DEV_SD is required for reading from hard drives. It is possible that there are other modules which you will need.

This post does not aim to be a guide to configuring your own kernel however, so if you do decide to build a custom kernel you’ll have to seek out other guides to create a kernel which is just right for your needs.

The second way to setup the kernel configuration makes more use of Guix’s features and allows you to share configuration segments between different kernels. For example, all machines using EFI to boot have a number of EFI configuration flags that they need. It is likely that all the kernels will share a list of filesystems to support. By using variables it is easier to see at a glance what features are enabled and to make sure you don’t have features in one kernel but missing in another.

Left undiscussed however, is Guix’s initrd and its customization. It is likely that you’ll need to modify the initrd on a machine using a custom kernel, since certain modules which are expected to be built may not be available for inclusion into the initrd.


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4 Advanced package management

Guix is a functional package manager that offers many features beyond what more traditional package managers can do. To the uninitiated, those features might not have obvious use cases at first. The purpose of this chapter is to demonstrate some advanced package management concepts.

see Package Management in GNU Guix Reference Manual for a complete reference.


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4.1 Guix Profiles in Practice

Guix provides a very useful feature that may be quite foreign to newcomers: profiles. They are a way to group package installations together and all users on the same system are free to use as many profiles as they want.

Whether you’re a developer or not, you may find that multiple profiles bring you great power and flexibility. While they shift the paradigm somewhat compared to traditional package managers, they are very convenient to use once you’ve understood how to set them up.

If you are familiar with Python’s ‘virtualenv’, you can think of a profile as a kind of universal ‘virtualenv’ that can hold any kind of software whatsoever, not just Python software. Furthermore, profiles are self-sufficient: they capture all the runtime dependencies which guarantees that all programs within a profile will always work at any point in time.

Multiple profiles have many benefits:

Concretely, here follows some typical profiles:

Let’s dive in the set up!


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4.1.1 Basic setup with manifests

A Guix profile can be set up via a so-called manifest specification that looks like this:

(specifications->manifest
  '("package-1"
    ;; Version 1.3 of package-2.
    "package-2@1.3"
    ;; The "lib" output of package-3.
    "package-3:lib"
    ; ...
    "package-N"))

see Invoking guix package in GNU Guix Reference Manual, for the syntax details.

We can create a manifest specification per profile and install them this way:

GUIX_EXTRA_PROFILES=$HOME/.guix-extra-profiles
mkdir -p "$GUIX_EXTRA_PROFILES"/my-project # if it does not exist yet
guix package --manifest=/path/to/guix-my-project-manifest.scm --profile="$GUIX_EXTRA_PROFILES"/my-project/my-project

Here we set an arbitrary variable ‘GUIX_EXTRA_PROFILES’ to point to the directory where we will store our profiles in the rest of this article.

Placing all your profiles in a single directory, with each profile getting its own sub-directory, is somewhat cleaner. This way, each sub-directory will contain all the symlinks for precisely one profile. Besides, "looping over profiles" becomes obvious from any programming language (e.g. a shell script) by simply looping over the sub-directories of ‘$GUIX_EXTRA_PROFILES’.

Note that it’s also possible to loop over the output of

guix package --list-profiles

although you’ll probably have to filter out ‘~/.config/guix/current’.

To enable all profiles on login, add this to your ‘~/.bash_profile’ (or similar):

for i in $GUIX_EXTRA_PROFILES/*; do
  profile=$i/$(basename "$i")
  if [ -f "$profile"/etc/profile ]; then
    GUIX_PROFILE="$profile"
    . "$GUIX_PROFILE"/etc/profile
  fi
  unset profile
done

Note to Guix System users: the above reflects how your default profile ‘~/.guix-profile’ is activated from ‘/etc/profile’, that latter being loaded by ‘~/.bashrc’ by default.

You can obviously choose to only enable a subset of them:

for i in "$GUIX_EXTRA_PROFILES"/my-project-1 "$GUIX_EXTRA_PROFILES"/my-project-2; do
  profile=$i/$(basename "$i")
  if [ -f "$profile"/etc/profile ]; then
    GUIX_PROFILE="$profile"
    . "$GUIX_PROFILE"/etc/profile
  fi
  unset profile
done

When a profile is off, it’s straightforward to enable it for an individual shell without "polluting" the rest of the user session:

GUIX_PROFILE="path/to/my-project" ; . "$GUIX_PROFILE"/etc/profile

The key to enabling a profile is to source its ‘etc/profile’ file. This file contains shell code that exports the right environment variables necessary to activate the software contained in the profile. It is built automatically by Guix and meant to be sourced. It contains the same variables you would get if you ran:

guix package --search-paths=prefix --profile=$my_profile"

Once again, see (see Invoking guix package in GNU Guix Reference Manual) for the command line options.

To upgrade a profile, simply install the manifest again:

guix package -m /path/to/guix-my-project-manifest.scm -p "$GUIX_EXTRA_PROFILES"/my-project/my-project

To upgrade all profiles, it’s easy enough to loop over them. For instance, assuming your manifest specifications are stored in ‘~/.guix-manifests/guix-$profile-manifest.scm’, with ‘$profile’ being the name of the profile (e.g. "project1"), you could do the following in Bourne shell:

for profile in "$GUIX_EXTRA_PROFILES"/*; do
  guix package --profile="$profile" --manifest="$HOME/.guix-manifests/guix-$profile-manifest.scm"
done

Each profile has its own generations:

guix package -p "$GUIX_EXTRA_PROFILES"/my-project/my-project --list-generations

You can roll-back to any generation of a given profile:

guix package -p "$GUIX_EXTRA_PROFILES"/my-project/my-project --switch-generations=17

Finally, if you want to switch to a profile without inheriting from the current environment, you can activate it from an empty shell:

env -i $(which bash) --login --noprofile --norc
. my-project/etc/profile

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4.1.2 Required packages

Activating a profile essentially boils down to exporting a bunch of environmental variables. This is the role of the ‘etc/profile’ within the profile.

Note: Only the environmental variables of the packages that consume them will be set.

For instance, ‘MANPATH’ won’t be set if there is no consumer application for man pages within the profile. So if you need to transparently access man pages once the profile is loaded, you’ve got two options:

The same is true for ‘INFOPATH’ (you can install ‘info-reader’), ‘PKG_CONFIG_PATH’ (install ‘pkg-config’), etc.


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4.1.3 Default profile

What about the default profile that Guix keeps in ‘~/.guix-profile’?

You can assign it the role you want. Typically you would install the manifest of the packages you want to use all the time.

Alternatively, you could keep it "manifest-less" for throw-away packages that you would just use for a couple of days. This way makes it convenient to run

guix install package-foo
guix upgrade package-bar

without having to specify the path to a profile.


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4.1.4 The benefits of manifests

Manifests are a convenient way to keep your package lists around and, say, to synchronize them across multiple machines using a version control system.

A common complaint about manifests is that they can be slow to install when they contain large number of packages. This is especially cumbersome when you just want get an upgrade for one package within a big manifest.

This is one more reason to use multiple profiles, which happen to be just perfect to break down manifests into multiple sets of semantically connected packages. Using multiple, small profiles provides more flexibility and usability.

Manifests come with multiple benefits. In particular, they ease maintenance:

It’s important to understand that while manifests can be used to declare profiles, they are not strictly equivalent: profiles have the side effect that they "pin" packages in the store, which prevents them from being garbage-collected (see Invoking guix gc in GNU Guix Reference Manual) and ensures that they will still be available at any point in the future.

Let’s take an example:

  1. We have an environment for hacking on a project for which there isn’t a Guix package yet. We build the environment using a manifest, and then run guix environment -m manifest.scm. So far so good.
  2. Many weeks pass and we have run a couple of guix pull in the mean time. Maybe a dependency from our manifest has been updated; or we may have run guix gc and some packages needed by our manifest have been garbage-collected.
  3. Eventually, we set to work on that project again, so we run guix environment -m manifest.scm. But now we have to wait for Guix to build and install stuff!

Ideally, we could spare the rebuild time. And indeed we can, all we need is to install the manifest to a profile and use GUIX_PROFILE=/the/profile; . "$GUIX_PROFILE"/etc/profile as explained above: this guarantees that our hacking environment will be available at all times.

Security warning: While keeping old profiles around can be convenient, keep in mind that outdated packages may not have received the latest security fixes.


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4.1.5 Reproducible profiles

To reproduce a profile bit-for-bit, we need two pieces of information:

Indeed, manifests alone might not be enough: different Guix versions (or different channels) can produce different outputs for a given manifest.

You can output the Guix channel specification with ‘guix describe --format=channels’. Save this to a file, say ‘channel-specs.scm’.

On another computer, you can use the channel specification file and the manifest to reproduce the exact same profile:

GUIX_EXTRA_PROFILES=$HOME/.guix-extra-profiles
GUIX_EXTRA=$HOME/.guix-extra

mkdir "$GUIX_EXTRA"/my-project
guix pull --channels=channel-specs.scm --profile "$GUIX_EXTRA/my-project/guix"

mkdir -p "$GUIX_EXTRA_PROFILES/my-project"
"$GUIX_EXTRA"/my-project/guix/bin/guix package --manifest=/path/to/guix-my-project-manifest.scm --profile="$GUIX_EXTRA_PROFILES"/my-project/my-project

It’s safe to delete the Guix channel profile you’ve just installed with the channel specification, the project profile does not depend on it.


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5 Acknowledgments

Guix is based on the Nix package manager, which was designed and implemented by Eelco Dolstra, with contributions from other people (see the nix/AUTHORS file in Guix.) Nix pioneered functional package management, and promoted unprecedented features, such as transactional package upgrades and rollbacks, per-user profiles, and referentially transparent build processes. Without this work, Guix would not exist.

The Nix-based software distributions, Nixpkgs and NixOS, have also been an inspiration for Guix.

GNU Guix itself is a collective work with contributions from a number of people. See the AUTHORS file in Guix for more information on these fine people. The THANKS file lists people who have helped by reporting bugs, taking care of the infrastructure, providing artwork and themes, making suggestions, and more—thank you!

This document includes adapted sections from articles that have previously been published on the Guix blog at https://guix.gnu.org/blog.


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Appendix A GNU Free Documentation License

Version 1.3, 3 November 2008
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
  1. PREAMBLE

    The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

    This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

  2. APPLICABILITY AND DEFINITIONS

    This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

    A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

    A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document’s overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

    The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

    The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

    A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.

    Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

    The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work’s title, preceding the beginning of the body of the text.

    The “publisher” means any person or entity that distributes copies of the Document to the public.

    A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

    The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

  3. VERBATIM COPYING

    You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

    You may also lend copies, under the same conditions stated above, and you may publicly display copies.

  4. COPYING IN QUANTITY

    If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

    If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

    If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

    It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

  5. MODIFICATIONS

    You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

    1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
    2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
    3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
    4. Preserve all the copyright notices of the Document.
    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
    6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document’s license notice.
    8. Include an unaltered copy of this License.
    9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
    10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
    11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
    12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
    13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
    14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
    15. Preserve any Warranty Disclaimers.

    If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice. These titles must be distinct from any other section titles.

    You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

    You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

    The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

  6. COMBINING DOCUMENTS

    You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

    The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

    In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”

  7. COLLECTIONS OF DOCUMENTS

    You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

  8. AGGREGATION WITH INDEPENDENT WORKS

    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

  9. TRANSLATION

    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

    If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

  10. TERMINATION

    You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

  11. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

  12. RELICENSING

    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

  Copyright (C)  year  your name.
  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''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with…Texts.” line with this:

    with the Invariant Sections being list their titles, with
    the Front-Cover Texts being list, and with the Back-Cover Texts
    being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.


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license, GNU Free Documentation License: GNU Free Documentation License

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packaging: Packaging

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Scheme, crash course: A Scheme Crash Course

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