10.15 Invoking guix system

Once you have written an operating system declaration as seen in the previous section, it can be instantiated using the guix system command. The synopsis is:

guix system options… action file

file must be the name of a file containing an operating-system declaration. action specifies how the operating system is instantiated. Currently the following values are supported:

search

Display available service type definitions that match the given regular expressions, sorted by relevance:

$ guix system search console
name: console-fonts
location: gnu/services/base.scm:806:2
extends: shepherd-root
description: Install the given fonts on the specified ttys (fonts are per
+ virtual console on GNU/Linux).  The value of this service is a list of
+ tty/font pairs.  The font can be the name of a font provided by the `kbd'
+ package or any valid argument to `setfont', as in this example:
+
+      '(("tty1" . "LatGrkCyr-8x16")
+        ("tty2" . (file-append
+                      font-tamzen
+                      "/share/kbd/consolefonts/TamzenForPowerline10x20.psf"))
+        ("tty3" . (file-append
+                      font-terminus
+                      "/share/consolefonts/ter-132n"))) ; for HDPI
relevance: 9

name: mingetty
location: gnu/services/base.scm:1190:2
extends: shepherd-root
description: Provide console login using the `mingetty' program.
relevance: 2

name: login
location: gnu/services/base.scm:860:2
extends: pam
description: Provide a console log-in service as specified by its
+ configuration value, a `login-configuration' object.
relevance: 2

…

As for guix package --search, the result is written in recutils format, which makes it easy to filter the output (see GNU recutils databases in GNU recutils manual).

reconfigure

Build the operating system described in file, activate it, and switch to it³¹.

Note: It is highly recommended to run guix pull once before you run guix system reconfigure for the first time (see Invoking guix pull). Failing to do that you would see an older version of Guix once reconfigure has completed.

This effects all the configuration specified in file: user accounts, system services, global package list, setuid programs, etc. The command starts system services specified in file that are not currently running; if a service is currently running this command will arrange for it to be upgraded the next time it is stopped (e.g. by herd stop X or herd restart X).

This command creates a new generation whose number is one greater than the current generation (as reported by guix system list-generations). If that generation already exists, it will be overwritten. This behavior mirrors that of guix package (see Invoking guix package).

It also adds a bootloader menu entry for the new OS configuration, —unless --no-bootloader is passed. For GRUB, it moves entries for older configurations to a submenu, allowing you to choose an older system generation at boot time should you need it.

Upon completion, the new system is deployed under /run/current-system. This directory contains provenance meta-data: the list of channels in use (see Channels) and file itself, when available. You can view it by running:

guix system describe

This information is useful should you later want to inspect how this particular generation was built. In fact, assuming file is self-contained, you can later rebuild generation n of your operating system with:

guix time-machine \
  -C /var/guix/profiles/system-n-link/channels.scm -- \
  system reconfigure \
  /var/guix/profiles/system-n-link/configuration.scm

You can think of it as some sort of built-in version control! Your system is not just a binary artifact: it carries its own source. See provenance-service-type, for more information on provenance tracking.

By default, reconfigure prevents you from downgrading your system, which could (re)introduce security vulnerabilities and also cause problems with “stateful” services such as database management systems. You can override that behavior by passing --allow-downgrades.

switch-generation

Switch to an existing system generation. This action atomically switches the system profile to the specified system generation. It also rearranges the system’s existing bootloader menu entries. It makes the menu entry for the specified system generation the default, and it moves the entries for the other generations to a submenu, if supported by the bootloader being used. The next time the system boots, it will use the specified system generation.

The bootloader itself is not being reinstalled when using this command. Thus, the installed bootloader is used with an updated configuration file.

The target generation can be specified explicitly by its generation number. For example, the following invocation would switch to system generation 7:

guix system switch-generation 7

The target generation can also be specified relative to the current generation with the form +N or -N, where +3 means “3 generations ahead of the current generation,” and -1 means “1 generation prior to the current generation.” When specifying a negative value such as -1, you must precede it with -- to prevent it from being parsed as an option. For example:

guix system switch-generation -- -1

Currently, the effect of invoking this action is only to switch the system profile to an existing generation and rearrange the bootloader menu entries. To actually start using the target system generation, you must reboot after running this action. In the future, it will be updated to do the same things as reconfigure, like activating and deactivating services.

This action will fail if the specified generation does not exist.

roll-back

Switch to the preceding system generation. The next time the system boots, it will use the preceding system generation. This is the inverse of reconfigure, and it is exactly the same as invoking switch-generation with an argument of -1.

Currently, as with switch-generation, you must reboot after running this action to actually start using the preceding system generation.

delete-generations

Delete system generations, making them candidates for garbage collection (see Invoking guix gc, for information on how to run the “garbage collector”).

This works in the same way as ‘guix package --delete-generations’ (see --delete-generations). With no arguments, all system generations but the current one are deleted:

guix system delete-generations

You can also select the generations you want to delete. The example below deletes all the system generations that are more than two months old:

guix system delete-generations 2m

Running this command automatically reinstalls the bootloader with an updated list of menu entries—e.g., the “old generations” sub-menu in GRUB no longer lists the generations that have been deleted.

build

Build the derivation of the operating system, which includes all the configuration files and programs needed to boot and run the system. This action does not actually install anything.

init

Populate the given directory with all the files necessary to run the operating system specified in file. This is useful for first-time installations of Guix System. For instance:

guix system init my-os-config.scm /mnt

copies to /mnt all the store items required by the configuration specified in my-os-config.scm. This includes configuration files, packages, and so on. It also creates other essential files needed for the system to operate correctly—e.g., the /etc, /var, and /run directories, and the /bin/sh file.

This command also installs bootloader on the targets specified in my-os-config, unless the --no-bootloader option was passed.

vm

Build a virtual machine (VM) that contains the operating system declared in file, and return a script to run that VM.

Note: The vm action and others below can use KVM support in the Linux-libre kernel. Specifically, if the machine has hardware virtualization support, the corresponding KVM kernel module should be loaded, and the /dev/kvm device node must exist and be readable and writable by the user and by the build users of the daemon (see Build Environment Setup).

Arguments given to the script are passed to QEMU as in the example below, which enables networking and requests 1 GiB of RAM for the emulated machine:

$ /gnu/store/…-run-vm.sh -m 1024 -smp 2 -nic user,model=virtio-net-pci

It’s possible to combine the two steps into one:

$ $(guix system vm my-config.scm) -m 1024 -smp 2 -nic user,model=virtio-net-pci

The VM shares its store with the host system.

By default, the root file system of the VM is mounted volatile; the --persistent option can be provided to make it persistent instead. In that case, the VM disk-image file will be copied from the store to the TMPDIR directory to make it writable.

Additional file systems can be shared between the host and the VM using the --share and --expose command-line options: the former specifies a directory to be shared with write access, while the latter provides read-only access to the shared directory.

The example below creates a VM in which the user’s home directory is accessible read-only, and where the /exchange directory is a read-write mapping of $HOME/tmp on the host:

guix system vm my-config.scm \
   --expose=$HOME --share=$HOME/tmp=/exchange

On GNU/Linux, the default is to boot directly to the kernel; this has the advantage of requiring only a very tiny root disk image since the store of the host can then be mounted.

The --full-boot option forces a complete boot sequence, starting with the bootloader. This requires more disk space since a root image containing at least the kernel, initrd, and bootloader data files must be created.

The --image-size option can be used to specify the size of the image.

The --no-graphic option will instruct guix system to spawn a headless VM that will use the invoking tty for IO. Among other things, this enables copy-pasting, and scrollback. Use the ctrl-a prefix to issue QEMU commands; e.g. ctrl-a h prints a help, ctrl-a x quits the VM, and ctrl-a c switches between the QEMU monitor and the VM.

image

The image command can produce various image types. The image type can be selected using the --image-type option. It defaults to efi-raw. When its value is iso9660, the --label option can be used to specify a volume ID with image. By default, the root file system of a disk image is mounted non-volatile; the --volatile option can be provided to make it volatile instead. When using image, the bootloader installed on the generated image is taken from the provided operating-system definition. The following example demonstrates how to generate an image that uses the grub-efi-bootloader bootloader and boot it with QEMU:

image=$(guix system image --image-type=qcow2 \
        gnu/system/examples/lightweight-desktop.tmpl)
cp $image /tmp/my-image.qcow2
chmod +w /tmp/my-image.qcow2
qemu-system-x86_64 -enable-kvm -hda /tmp/my-image.qcow2 -m 1000 \
                   -bios $(guix build ovmf)/share/firmware/ovmf_x64.bin

When using the efi-raw image type, a raw disk image is produced; it can be copied as is to a USB stick, for instance. Assuming /dev/sdc is the device corresponding to a USB stick, one can copy the image to it using the following command:

# dd if=$(guix system image my-os.scm) of=/dev/sdc status=progress

The --list-image-types command lists all the available image types.

When using the qcow2 image type, the returned image is in qcow2 format, which the QEMU emulator can efficiently use. See Running Guix in a VM, for more information on how to run the image in a virtual machine. The grub-bootloader bootloader is always used independently of what is declared in the operating-system file passed as argument. This is to make it easier to work with QEMU, which uses the SeaBIOS BIOS by default, expecting a bootloader to be installed in the Master Boot Record (MBR).

When using the docker image type, a Docker image is produced. Guix builds the image from scratch, not from a pre-existing Docker base image. As a result, it contains exactly what you define in the operating system configuration file. You can then load the image and launch a Docker container using commands like the following:

image_id="$(docker load < guix-system-docker-image.tar.gz)"
container_id="$(docker create $image_id)"
docker start $container_id

This command starts a new Docker container from the specified image. It will boot the Guix system in the usual manner, which means it will start any services you have defined in the operating system configuration. You can get an interactive shell running in the container using docker exec:

docker exec -ti $container_id /run/current-system/profile/bin/bash --login

Depending on what you run in the Docker container, it may be necessary to give the container additional permissions. For example, if you intend to build software using Guix inside of the Docker container, you may need to pass the --privileged option to docker create.

Last, the --network option applies to guix system docker-image: it produces an image where network is supposedly shared with the host, and thus without services like nscd or NetworkManager.

container

Return a script to run the operating system declared in file within a container. Containers are a set of lightweight isolation mechanisms provided by the kernel Linux-libre. Containers are substantially less resource-demanding than full virtual machines since the kernel, shared objects, and other resources can be shared with the host system; this also means they provide thinner isolation.

Currently, the script must be run as root in order to support more than a single user and group. The container shares its store with the host system.

As with the vm action (see guix system vm), additional file systems to be shared between the host and container can be specified using the --share and --expose options:

guix system container my-config.scm \
   --expose=$HOME --share=$HOME/tmp=/exchange

Note: This option requires Linux-libre 3.19 or newer.

options can contain any of the common build options (see Common Build Options). In addition, options can contain one of the following:

--expression=expr

-e expr

Consider the operating-system expr evaluates to. This is an alternative to specifying a file which evaluates to an operating system. This is used to generate the Guix system installer see Building the Installation Image).

--system=system

-s system

Attempt to build for system instead of the host system type. This works as per guix build (see Invoking guix build).

--derivation

-d

Return the derivation file name of the given operating system without building anything.

--save-provenance

As discussed above, guix system init and guix system reconfigure always save provenance information via a dedicated service (see provenance-service-type). However, other commands don’t do that by default. If you wish to, say, create a virtual machine image that contains provenance information, you can run:

guix system image -t qcow2 --save-provenance config.scm

That way, the resulting image will effectively “embed its own source” in the form of meta-data in /run/current-system. With that information, one can rebuild the image to make sure it really contains what it pretends to contain; or they could use that to derive a variant of the image.

--image-type=type

-t type

For the image action, create an image with given type.

When this option is omitted, guix system uses the efi-raw image type.

--image-type=iso9660 produces an ISO-9660 image, suitable for burning on CDs and DVDs.

--image-size=size

For the image action, create an image of the given size. size may be a number of bytes, or it may include a unit as a suffix (see size specifications in GNU Coreutils).

When this option is omitted, guix system computes an estimate of the image size as a function of the size of the system declared in file.

--network

-N

For the container action, allow containers to access the host network, that is, do not create a network namespace.

--root=file

-r file

Make file a symlink to the result, and register it as a garbage collector root.

--skip-checks

Skip pre-installation safety checks.

By default, guix system init and guix system reconfigure perform safety checks: they make sure the file systems that appear in the operating-system declaration actually exist (see File Systems), and that any Linux kernel modules that may be needed at boot time are listed in initrd-modules (see Initial RAM Disk). Passing this option skips these tests altogether.

--allow-downgrades

Instruct guix system reconfigure to allow system downgrades.

By default, reconfigure prevents you from downgrading your system. It achieves that by comparing the provenance info of your system (shown by guix system describe) with that of your guix command (shown by guix describe). If the commits for guix are not descendants of those used for your system, guix system reconfigure errors out. Passing --allow-downgrades allows you to bypass these checks.

Note: Make sure you understand its security implications before using --allow-downgrades.

--on-error=strategy

Apply strategy when an error occurs when reading file. strategy may be one of the following:

nothing-special

Report the error concisely and exit. This is the default strategy.

backtrace

Likewise, but also display a backtrace.

debug

Report the error and enter Guile’s debugger. From there, you can run commands such as ,bt to get a backtrace, ,locals to display local variable values, and more generally inspect the state of the program. See Debug Commands in GNU Guile Reference Manual, for a list of available debugging commands.

Once you have built, configured, re-configured, and re-re-configured your Guix installation, you may find it useful to list the operating system generations available on disk—and that you can choose from the bootloader boot menu:

describe

Describe the running system generation: its file name, the kernel and bootloader used, etc., as well as provenance information when available.

Note: The running system generation—referred to by /run/current-system—is not necessarily the current system generation—referred to by /var/guix/profiles/system: it differs when, for instance, you chose from the bootloader menu to boot an older generation.

It can also differ from the booted system generation—referred to by /run/booted-system—for instance because you reconfigured the system in the meantime.

list-generations

List a summary of each generation of the operating system available on disk, in a human-readable way. This is similar to the --list-generations option of guix package (see Invoking guix package).

Optionally, one can specify a pattern, with the same syntax that is used in guix package --list-generations, to restrict the list of generations displayed. For instance, the following command displays generations that are up to 10 days old:

$ guix system list-generations 10d

The guix system command has even more to offer! The following sub-commands allow you to visualize how your system services relate to each other:

extension-graph

Emit to standard output the service extension graph of the operating system defined in file (see Service Composition, for more information on service extensions). By default the output is in Dot/Graphviz format, but you can choose a different format with --graph-backend, as with guix graph (see --backend):

The command:

$ guix system extension-graph file | xdot -

shows the extension relations among services.

shepherd-graph

Emit to standard output the dependency graph of shepherd services of the operating system defined in file. See Shepherd Services, for more information and for an example graph.

Again, the default output format is Dot/Graphviz, but you can pass --graph-backend to select a different one.