GNU Guix

Inherited from the design of Nix, most of the content of the package manager is kept in a directory /gnu/store where only the Guix daemon has write-access. This is achieved via specialised bind mounts, where the Store as a file system is mounted read only, prohibiting interference even from the root user, while the Guix daemon remounts the Store as read/writable in its own private namespace. Guix talks with this daemon to build things or fetch substitutes which are all kept in the store.

Guix - like Nix - has built-in garbage collection facilities to help prune dead store items and keep the live ones.[11]

This is an example of a package definition for the hello-package:

(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+)))

It is written using Guile. The package recipes can easily be inspected (running e.g. guix edit hello) and changed in Guix, making the system transparent and very easily hackable.

Inherited from the design of Nix, all manipulation of store items is independent of each other, and the directories of the store begin with a base32-encoded hash of the source code of the derivation along with its inputs.

Guix package uses profiles generations, which are a collection of symlinks to specific store items together comprising what the user has installed into the profile. Every time a package is installed or removed, a new generation will be built.

E.g. the profile of a user who only installed GNU Hello contains links to the store item which holds the version of hello installed with the currently used guix.

E.g. on version c087a90e06d7b9451f802323e24deb1862a21e0f of guix, this corresponds to the following item: /gnu/store/md2plii4g5sk66wg9cgwc964l3xwhrm9-hello-2.10 (built from the recipe above).

In addition to symlinks, each profile guix builds also contains a union of all the info-manuals, man-pages, icons, fonts, etc. so that the user can browse documentation and have access to all the icons and fonts installed.

The default symlinks to profile generations are stored under /var/guix in the filesystem.

The user can create any number of profiles by invoking guix package -p PROFILE-NAME COMMAND. A new directory with the profile-name as well as profile-generation-symlinks will then be created in the current directory.

Guix package enables instantaneous roll-back to a previous profile generation via changing the symlink to an earlier profile generation.[12] Profiles are also stored in the store e.g. this item is a profile containing hello above: /gnu/store/b4wipjlsapvnijmbawl7sh76087vpl4n-profile (built and activated when running guix install hello).

Guix environment enables the user to easily enter an environment where all the necessary packages for development of software are present without clogging up the users default profile with dependencies for multiple projects.[13]

E.g. running guix environment hello enters a throw-away environment where everything needed to compile hello on guix is present (gcc, guile, etc.).

If you want a persistent gc-rooted environment that is not garbage collected on the next run of guix gc you can create a root:

E.g. running guix environment --root=hello-root hello enters an environment where everything needed to compile guix is present (gcc, guile, etc.) and registered as a root in the current directory (by symlinking to the items in the store).

Guix pack enables the user to bundle together store items and output them as a docker binary image, a relocatable tarball or a squashfs binary.[14]

Guix graph enables the user to view different graphs of the packages and their dependencies.[15]

The following CPU architectures are supported: IA-32, x64, AArch32, AArch64[28] and in April 2019 work was in progress for POWER9 support.[29]

System services are a core feature in Guix System that enable the user to declaratively compose the configuration of daemons and background services and easily specify the relevant configurations.

This enables the user to within a single configuration file declare the whole OS (e.g, to have a tor proxy, an sshd server, and a webserver serving guix-web via nginx on a specific port at bootup).

System services can[30]:

• generate files in the filesystem (needed by some applications e.g. files in /etc)
• run any code for setting up daemons
• create specific user and group accounts (e.g. a database user for postgresql)

Ricardo Wurmus, one of the maintainers, explains the extendability like this:

Services can extend one another, which allows us to define ways to set up complex applications, for example, that require a web server, user accounts, application-specific daemons, a database, udev rules, etc — all with just one service type.

— [31]

All the services are defined using Guile Scheme.[32] The list of services continue to grow and as of 1.0.0 the list of services includes the following[33]:

• Base Services: Essential system services.
• Scheduled Job Execution: The mcron service.
• Log Rotation: The rottlog service.
• Networking Services: Network setup, SSH daemon, etc.
• X Window: Graphical display.
• Printing Services: Local and remote printer support.
• Desktop Services: D-Bus and desktop services.
• Sound Services: ALSA and Pulseaudio services.
• Database Services: SQL databases, key-value stores, etc.
• Mail Services: IMAP, POP3, SMTP, and all that.
• Messaging Services: Messaging services.
• Telephony Services: Telephony services.
• Monitoring Services: Monitoring services.
• Kerberos Services: Kerberos services.
• LDAP Services: LDAP services.
• Web Services: Web servers.
• Certificate Services: TLS certificates via Let’s Encrypt.
• DNS Services: DNS daemons.
• VPN Services: VPN daemons.
• Network File System: NFS related services.
• Continuous Integration: The Cuirass service.
• Power Management Services: Extending battery life.
• Audio Services: The MPD.
• Virtualization Services: Virtualization services.
• Version Control Services: Providing remote access to Git repositories.
• Game Services: Game servers.
• Miscellaneous Services: Other services.

Guix System uses the GNU Daemon Shepherd as its init system, which is developed in tandem with Guix and is written in Guile as well. It was previously known as "dmd", which stood for "Daemon managing Daemons" or "Daemons-managing Daemon", but changed names to avoid collision with the Digital Mars D compiler.[34]

Shepherd supplies user-space functionality asynchronously as services, which under Shepherd are generic functions and object data types that are exported for use by the Shepherd to extend the base operating system in some defined way. In contrast to systemd, a userspace shepherd process runs as that user. Core to the Shepherd model of user space initialisation is the concept of the extension, a form of composability where services are designed to be layered onto other services, augmenting them with more elaborate or specialised behaviours as desired.[35] This expresses the instantiation-based dependency relationships found in many modern init systems,[36] making the system modular, but also allows services to interact variadically with other services in arbitrary ways.

Shepherd also provides so-called virtual services which allow dynamic dispatch over a class of related service objects, such as all those which instantiate a mail transfer agent (MTA) for the system.[37] A system governed via the Shepherd daemon can represent its user space as a directed acyclic graph, with the "system-service" − responsible for early phases of boot and init − as its root, and all subsequently initialised services as extensions to system-service's functionality, either directly or transitively over other services.[35][38]

Being both written and configured in Guile Scheme, GNU Shepherd is intended to be highly programmable by the system administrator, but it can also be used to manage per-user profiles of unprivileged daemons and services.[39] Its services and configuration are stored uniformly as object-oriented Scheme code, and while a core set of services are provided with the basic Guix System,[40] arbitrary new services can be flexibly declared, and through Guile's object system, GOOPS, existing services can be redefined at the user's discretion by asking the Shepherd to dynamically rewrite services in specified ways on instantiation.[41][42]

GNU Shepherd was originally designed to work with GNU Hurd, and was later adopted by Guix System.[43]

Guix System to date has only an unstable development git repository[44] shared with Guix but enables users or organizations to set up stable release channels themselves via the channel-feature.[45]

Packages in Guix are generally very up-to-date thanks to the lack of a package maintainer bottleneck: anyone can contribute an update subject to community approval and the process is assisted by tools such as guix refresh.[46]

Changes to the git repository are peer-reviewed by community members and committed by one of the 45 people with commit access.[47] In practice sometimes these builds cause system breakages for users because of a typo or similar error, but these are often solved within minutes. The way Guix pull operates means users retain a working system in the meantime.

If a system update should leave users with a broken system, users can easily roll back individual packages as well as the whole system state.[48] This means that a stable channel which is very common in other Linux distributions is no longer needed for users who are willing to report a bug and wait a few minutes, when trying to update via guix pull.

Jesse Smith from DistroWatch Weekly reviewed GuixSD 0.15.0, and said, "GuixSD has a package manager that I like", but criticized the limited hardware support and its limited documentation.[52] The documentation has since then been expanded and improved with videos[53] and a cookbook[54] in six languages with tutorials, how-to guides and examples.