Bootloader

The bootloader field describes the method that will be used to boot your system. Machines based on Intel processors can boot in “legacy” BIOS mode, as in the example above. However, more recent machines rely instead on the Unified Extensible Firmware Interface (UEFI) to boot. In that case, the bootloader field should contain something along these lines:

(bootloader-configuration
  (bootloader grub-efi-bootloader)
  (targets '("/boot/efi")))

See Bootloader Configuration, for more information on the available configuration options.

Globally-Visible Packages

The packages field lists packages that will be globally visible on the system, for all user accounts—i.e., in every user’s PATH environment variable—in addition to the per-user profiles (see Invoking guix package). The %base-packages variable provides all the tools one would expect for basic user and administrator tasks—including the GNU Core Utilities, the GNU Networking Utilities, the mg lightweight text editor, find, grep, etc. The example above adds GNU Screen to those, taken from the (gnu packages screen) module (see Package Modules). The (list package output) syntax can be used to add a specific output of a package:

(use-modules (gnu packages))
(use-modules (gnu packages dns))

(operating-system
  ;; ...
  (packages (cons (list isc-bind "utils")
                  %base-packages)))

Referring to packages by variable name, like isc-bind above, has the advantage of being unambiguous; it also allows typos and such to be diagnosed right away as “unbound variables”. The downside is that one needs to know which module defines which package, and to augment the use-package-modules line accordingly. To avoid that, one can use the specification->package procedure of the (gnu packages) module, which returns the best package for a given name or name and version:

(use-modules (gnu packages))

(operating-system
  ;; ...
  (packages (append (map specification->package
                         '("tcpdump" "htop" "gnupg@2.0"))
                    %base-packages)))

System Services

The services field lists system services to be made available when the system starts (see Services). The operating-system declaration above specifies that, in addition to the basic services, we want the OpenSSH secure shell daemon listening on port 2222 (see openssh-service-type). Under the hood, openssh-service-type arranges so that sshd is started with the right command-line options, possibly with supporting configuration files generated as needed (see Defining Services).

Occasionally, instead of using the base services as is, you will want to customize them. To do this, use modify-services (see modify-services) to modify the list.

For example, suppose you want to modify guix-daemon and Mingetty (the console log-in) in the %base-services list (see %base-services). To do that, you can write the following in your operating system declaration:

(define %my-services
  ;; My very own list of services.
  (modify-services %base-services
    (guix-service-type config =>
                       (guix-configuration
                        (inherit config)
                        ;; Fetch substitutes from example.org.
                        (substitute-urls
                          (list "https://example.org/guix"
                                "https://ci.guix.gnu.org"))))
    (mingetty-service-type config =>
                           (mingetty-configuration
                            (inherit config)
                            ;; Automatically log in as "guest".
                            (auto-login "guest")))))

(operating-system
  ;; …
  (services %my-services))

This changes the configuration—i.e., the service parameters—of the guix-service-type instance, and that of all the mingetty-service-type instances in the %base-services list (see see the cookbook for how to auto-login one user to a specific TTY in GNU Guix Cookbook)). Observe how this is accomplished: first, we arrange for the original configuration to be bound to the identifier config in the body, and then we write the body so that it evaluates to the desired configuration. In particular, notice how we use inherit to create a new configuration which has the same values as the old configuration, but with a few modifications.

The configuration for a typical “desktop” usage, with an encrypted root partition, a swap file on the root partition, the X11 display server, GNOME and Xfce (users can choose which of these desktop environments to use at the log-in screen by pressing F1), network management, power management, and more, would look like this:

;; This is an operating system configuration template
;; for a "desktop" setup with GNOME and Xfce where the
;; root partition is encrypted with LUKS, and a swap file.

(use-modules (gnu) (gnu system nss) (guix utils))
(use-service-modules desktop sddm xorg)
(use-package-modules certs gnome)

(operating-system
  (host-name "antelope")
  (timezone "Europe/Paris")
  (locale "en_US.utf8")

  ;; Choose US English keyboard layout.  The "altgr-intl"
  ;; variant provides dead keys for accented characters.
  (keyboard-layout (keyboard-layout "us" "altgr-intl"))

  ;; Use the UEFI variant of GRUB with the EFI System
  ;; Partition mounted on /boot/efi.
  (bootloader (bootloader-configuration
                (bootloader grub-efi-bootloader)
                (targets '("/boot/efi"))
                (keyboard-layout keyboard-layout)))

  ;; Specify a mapped device for the encrypted root partition.
  ;; The UUID is that returned by 'cryptsetup luksUUID'.
  (mapped-devices
   (list (mapped-device
          (source (uuid "12345678-1234-1234-1234-123456789abc"))
          (target "my-root")
          (type luks-device-mapping))))

  (file-systems (append
                 (list (file-system
                         (device (file-system-label "my-root"))
                         (mount-point "/")
                         (type "ext4")
                         (dependencies mapped-devices))
                       (file-system
                         (device (uuid "1234-ABCD" 'fat))
                         (mount-point "/boot/efi")
                         (type "vfat")))
                 %base-file-systems))

  ;; Specify a swap file for the system, which resides on the
  ;; root file system.
  (swap-devices (list (swap-space
                       (target "/swapfile"))))

  ;; Create user `bob' with `alice' as its initial password.
  (users (cons (user-account
                (name "bob")
                (comment "Alice's brother")
                (password (crypt "alice" "$6$abc"))
                (group "students")
                (supplementary-groups '("wheel" "netdev"
                                        "audio" "video")))
               %base-user-accounts))

  ;; Add the `students' group
  (groups (cons* (user-group
                  (name "students"))
                 %base-groups))

  ;; This is where we specify system-wide packages.
  (packages (append (list
                     ;; for HTTPS access
                     nss-certs
                     ;; for user mounts
                     gvfs)
                    %base-packages))

  ;; Add GNOME and Xfce---we can choose at the log-in screen
  ;; by clicking the gear.  Use the "desktop" services, which
  ;; include the X11 log-in service, networking with
  ;; NetworkManager, and more.
  (services (if (target-x86-64?)
                (append (list (service gnome-desktop-service-type)
                              (service xfce-desktop-service-type)
                              (set-xorg-configuration
                               (xorg-configuration
                                (keyboard-layout keyboard-layout))))
                        %desktop-services)

                ;; FIXME: Since GDM depends on Rust (gdm -> gnome-shell -> gjs
                ;; -> mozjs -> rust) and Rust is currently unavailable on
                ;; non-x86_64 platforms, we use SDDM and Mate here instead of
                ;; GNOME and GDM.
                (append (list (service mate-desktop-service-type)
                              (service xfce-desktop-service-type)
                              (set-xorg-configuration
                               (xorg-configuration
                                (keyboard-layout keyboard-layout))
                               sddm-service-type))
                        %desktop-services)))

  ;; Allow resolution of '.local' host names with mDNS.
  (name-service-switch %mdns-host-lookup-nss))

A graphical system with a choice of lightweight window managers instead of full-blown desktop environments would look like this:

;; This is an operating system configuration template
;; for a "desktop" setup without full-blown desktop
;; environments.

(use-modules (gnu) (gnu system nss))
(use-service-modules desktop)
(use-package-modules bootloaders certs emacs emacs-xyz ratpoison suckless wm
                     xorg)

(operating-system
  (host-name "antelope")
  (timezone "Europe/Paris")
  (locale "en_US.utf8")

  ;; Use the UEFI variant of GRUB with the EFI System
  ;; Partition mounted on /boot/efi.
  (bootloader (bootloader-configuration
                (bootloader grub-efi-bootloader)
                (targets '("/boot/efi"))))

  ;; Assume the target root file system is labelled "my-root",
  ;; and the EFI System Partition has UUID 1234-ABCD.
  (file-systems (append
                 (list (file-system
                         (device (file-system-label "my-root"))
                         (mount-point "/")
                         (type "ext4"))
                       (file-system
                         (device (uuid "1234-ABCD" 'fat))
                         (mount-point "/boot/efi")
                         (type "vfat")))
                 %base-file-systems))

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

  ;; Add a bunch of window managers; we can choose one at
  ;; the log-in screen with F1.
  (packages (append (list
                     ;; window managers
                     ratpoison i3-wm i3status dmenu
                     emacs emacs-exwm emacs-desktop-environment
                     ;; terminal emulator
                     xterm
                     ;; for HTTPS access
                     nss-certs)
                    %base-packages))

  ;; Use the "desktop" services, which include the X11
  ;; log-in service, networking with NetworkManager, and more.
  (services %desktop-services)

  ;; Allow resolution of '.local' host names with mDNS.
  (name-service-switch %mdns-host-lookup-nss))

This example refers to the /boot/efi file system by its UUID, 1234-ABCD. Replace this UUID with the right UUID on your system, as returned by the blkid command.

See Desktop Services, for the exact list of services provided by %desktop-services. See X.509 Certificates, for background information about the nss-certs package that is used here.

Again, %desktop-services is just a list of service objects. If you want to remove services from there, you can do so using the procedures for list filtering (see SRFI-1 Filtering and Partitioning in GNU Guile Reference Manual). For instance, the following expression returns a list that contains all the services in %desktop-services minus the Avahi service:

(remove (lambda (service)
          (eq? (service-kind service) avahi-service-type))
        %desktop-services)

Alternatively, the modify-services macro can be used:

(modify-services %desktop-services
  (delete avahi-service-type))

Instantiating the System

Assuming the operating-system declaration is stored in the my-system-config.scm file, the guix system reconfigure my-system-config.scm command instantiates that configuration, and makes it the default GRUB boot entry (see Invoking guix system).

Note: We recommend that you keep this my-system-config.scm file safe and under version control to easily track changes to your configuration.

The normal way to change the system configuration is by updating this file and re-running guix system reconfigure. One should never have to touch files in /etc or to run commands that modify the system state such as useradd or grub-install. In fact, you must avoid that since that would not only void your warranty but also prevent you from rolling back to previous versions of your system, should you ever need to.

Speaking of roll-back, each time you run guix system reconfigure, a new generation of the system is created—without modifying or deleting previous generations. Old system generations get an entry in the bootloader boot menu, allowing you to boot them in case something went wrong with the latest generation. Reassuring, no? The guix system list-generations command lists the system generations available on disk. It is also possible to roll back the system via the commands guix system roll-back and guix system switch-generation.

Although the guix system reconfigure command will not modify previous generations, you must take care when the current generation is not the latest (e.g., after invoking guix system roll-back), since the operation might overwrite a later generation (see Invoking guix system).

The Programming Interface

At the Scheme level, the bulk of an operating-system declaration is instantiated with the following monadic procedure (see The Store Monad):

Monadic Procedure: operating-system-derivation os

Return a derivation that builds os, an operating-system object (see Derivations).

The output of the derivation is a single directory that refers to all the packages, configuration files, and other supporting files needed to instantiate os.

This procedure is provided by the (gnu system) module. Along with (gnu services) (see Services), this module contains the guts of Guix System. Make sure to visit it!