.Dd January 1, 1980
.Dt nixos-rebuild 8
.Os
.Sh NAME
.Nm nixos-rebuild
.Nd reconfigure a NixOS machine
.
.
.
.Sh SYNOPSIS
.Nm
.Bro
.Cm switch | boot | test | build | dry-build | dry-activate | edit | build-vm | build-vm-with-bootloader | list-generations Op Fl -json
.Brc
.br
.Op Fl -upgrade | -upgrade-all
.Op Fl -install-bootloader
.Op Fl -no-build-nix
.Op Fl -fast
.Op Fl -rollback
.Op Fl -builders Ar builder-spec
.br
.Op Fl -flake Ar flake-uri
.Op Fl -no-flake
.Op Fl -override-input Ar input-name flake-uri
.br
.Op Fl -profile-name | p Ar name
.Op Fl -specialisation | c Ar name
.br
.Op Fl -build-host Va host
.Op Fl -target-host Va host
.Op Fl -use-remote-sudo
.br
.Op Fl -show-trace
.Op Fl I Va NIX_PATH
.Op Fl -verbose | v
.Op Fl -impure
.Op Fl -max-jobs | j Va number
.Op Fl -keep-failed | K
.Op Fl -keep-going | k
.
.
.
.Sh DESCRIPTION
This command updates the system so that it corresponds to the
configuration specified in
.Pa /etc/nixos/configuration.nix
or
.Pa /etc/nixos/flake.nix Ns
\&. Thus, every time you modify the configuration or any other NixOS module, you
must run
.Nm
to make the changes take effect. It builds the new system in
.Pa /nix/store Ns
, runs its activation script, and stop and (re)starts any system services if
needed. Please note that user services need to be started manually as they
aren't detected by the activation script at the moment.
.
.Pp
This command has one required argument, which specifies the desired
operation. It must be one of the following:
.Bl -tag -width indent
.It Cm switch
Build and activate the new configuration, and make it the boot default. That
is, the configuration is added to the GRUB boot menu as the default
menu entry, so that subsequent reboots will boot the system into the new
configuration. Previous configurations activated with
.Ic nixos-rebuild switch
or
.Ic nixos-rebuild boot
remain available in the GRUB menu.
.Pp
Note that if you are using specializations, running just
.Ic nixos-rebuild switch
will switch you back to the unspecialized, base system \(em in that case, you
might want to use this instead:
.Bd -literal -offset indent
$ nixos-rebuild switch --specialisation your-specialisation-name
.Ed
.Pp
This command will build all specialisations and make them bootable just
like regular
.Ic nixos-rebuild switch
does \(em the only thing different is that it will switch to given
specialisation instead of the base system; it can be also used to switch from
the base system into a specialised one, or to switch between specialisations.
.
.It Cm boot
Build the new configuration and make it the boot default (as with
.Ic nixos-rebuild switch Ns
), but do not activate it. That is, the system continues to run the previous
configuration until the next reboot.
.
.It Cm test
Build and activate the new configuration, but do not add it to the GRUB
boot menu. Thus, if you reboot the system (or if it crashes), you will
automatically revert to the default configuration (i.e. the
configuration resulting from the last call to
.Ic nixos-rebuild switch
or
.Ic nixos-rebuild boot Ns
).
.Pp
Note that if you are using specialisations, running just
.Ic nixos-rebuild test
will activate the unspecialised, base system \(em in that case, you might want
to use this instead:
.Bd -literal -offset indent
$ nixos-rebuild test --specialisation your-specialisation-name
.Ed
.Pp
This command can be also used to switch from the base system into a
specialised one, or to switch between specialisations.
.
.It Cm build
Build the new configuration, but neither activate it nor add it to the
GRUB boot menu. It leaves a symlink named
.Pa result
in the current directory, which points to the output of the top-level
.Dq system
derivation. This is essentially the same as doing
.Bd -literal -offset indent
$ nix-build /path/to/nixpkgs/nixos -A system
.Ed
.Pp
Note that you do not need to be root to run
.Ic nixos-rebuild build Ns
\&.
.
.It Cm dry-build
Show what store paths would be built or downloaded by any of the
operations above, but otherwise do nothing.
.
.It Cm dry-activate
Build the new configuration, but instead of activating it, show what
changes would be performed by the activation (i.e. by
.Ic nixos-rebuild test Ns
). For instance, this command will print which systemd units would be restarted.
The list of changes is not guaranteed to be complete.
.
.It Cm edit
Opens
.Pa configuration.nix
in the default editor.
.
.It Cm build-vm
Build a script that starts a NixOS virtual machine with the desired
configuration. It leaves a symlink
.Pa result
in the current directory that points (under
.Ql result/bin/run\- Ns Va hostname Ns \-vm Ns
)
at the script that starts the VM. Thus, to test a NixOS configuration in
a virtual machine, you should do the following:
.Bd -literal -offset indent
$ nixos-rebuild build-vm
$ ./result/bin/run-*-vm
.Ed
.Pp
The VM is implemented using the
.Ql qemu
package. For best performance, you should load the
.Ql kvm-intel
or
.Ql kvm-amd
kernel modules to get hardware virtualisation.
.Pp
The VM mounts the Nix store of the host through the 9P file system. The
host Nix store is read-only, so Nix commands that modify the Nix store
will not work in the VM. This includes commands such as
.Nm Ns
; to change the VM’s configuration, you must halt the VM and re-run the commands
above.
.Pp
The VM has its own ext3 root file system, which is automatically created when
the VM is first started, and is persistent across reboots of the VM. It is
stored in
.Ql ./ Ns Va hostname Ns .qcow2 Ns
\&.
.\" The entire file system hierarchy of the host is available in
.\" the VM under
.\" .Pa /hostfs Ns
.\" .
.
.It Cm build-vm-with-bootloader
Like
.Cm build-vm Ns
, but boots using the regular boot loader of your configuration (e.g. GRUB 1 or
2), rather than booting directly into the kernel and initial ramdisk of the
system. This allows you to test whether the boot loader works correctly. \
However, it does not guarantee that your NixOS configuration will boot
successfully on the host hardware (i.e., after running
.Ic nixos-rebuild switch Ns
), because the hardware and boot loader configuration in the VM are different.
The boot loader is installed on an automatically generated virtual disk
containing a
.Pa /boot
partition.
.
.It Cm list-generations Op Fl -json
List the available generations in a similar manner to the boot loader
menu. It shows the generation number, build date and time, NixOS version,
kernel version and the configuration revision. This is useful to get
information e.g. for which generation to roll back to with
.Ic nixos-rebuild switch Fl -generation Ar N
There is also a json version of output available.
.El
.
.
.
.Sh OPTIONS
.Bl -tag -width indent
.It Fl -upgrade , -upgrade-all
Update the root user's channel named
.Ql nixos
before rebuilding the system.
.Pp
In addition to the
.Ql nixos
channel, the root user's channels which have a file named
.Ql .update-on-nixos-rebuild
in their base directory will also be updated.
.Pp
Passing
.Fl -upgrade-all
updates all of the root user's channels.
.
.It Fl -install-bootloader
Causes the boot loader to be (re)installed on the device specified by the
relevant configuration options.
.
.It Fl -no-build-nix
Normally,
.Nm
first builds the
.Ql nixUnstable
attribute in Nixpkgs, and uses the resulting instance of the Nix package manager
to build the new system configuration. This is necessary if the NixOS modules
use features not provided by the currently installed version of Nix. This option
disables building a new Nix.
.
.It Fl -fast
Equivalent to
.Fl -no-build-nix Ns
\&. This option is useful if you call
.Nm
frequently (e.g. if you’re hacking on a NixOS module).
.
.It Fl -rollback
Instead of building a new configuration as specified by
.Pa /etc/nixos/configuration.nix Ns
, roll back to the previous configuration. (The previous configuration is
defined as the one before the “current” generation of the Nix profile
.Pa /nix/var/nix/profiles/system Ns
\&.)
.
.It Fl -builders Ar builder-spec
Allow ad-hoc remote builders for building the new system. This requires
the user executing
.Nm
(usually root) to be configured as a trusted user in the Nix daemon. This can be
achieved by using the
.Va nix.settings.trusted-users
NixOS option. Examples values for that option are described in the
.Dq Remote builds
chapter in the Nix manual, (i.e.
.Ql --builders \(dqssh://bigbrother x86_64-linux\(dq Ns
). By specifying an empty string existing builders specified in
.Pa /etc/nix/machines
can be ignored:
.Ql --builders \(dq\(dq
for example when they are not reachable due to network connectivity.
.
.It Fl -profile-name Ar name , Fl p Ar name
Instead of using the Nix profile
.Pa /nix/var/nix/profiles/system
to keep track of the current and previous system configurations, use
.Pa /nix/var/nix/profiles/system-profiles/ Ns Va name Ns
\&. When you use GRUB 2, for every system profile created with this flag, NixOS
will create a submenu named
.Dq NixOS - Profile Va name
in GRUB’s boot menu, containing the current and previous configurations of this profile.
.Pp
For instance, if you want to test a configuration file named
.Pa test.nix
without affecting the default system profile, you would do:
.Bd -literal -offset indent
$ nixos-rebuild switch -p test -I nixos-config=./test.nix
.Ed
.Pp
The new configuration will appear in the GRUB 2 submenu
.Dq NixOS - Profile 'test' Ns
\&.
.
.It Fl -specialisation Ar name , Fl c Ar name
Activates given specialisation; when not specified, switching and testing
will activate the base, unspecialised system.
.
.It Fl -build-host Ar host
Instead of building the new configuration locally, use the specified host
to perform the build. The host needs to be accessible with
.Ic ssh Ns ,
and must be able to perform Nix builds. If the option
.Fl -target-host
is not set, the build will be copied back to the local machine when done.
.Pp
Note that, if
.Fl -no-build-nix
is not specified, Nix will be built both locally and remotely. This is because
the configuration will always be evaluated locally even though the building
might be performed remotely.
.Pp
You can include a remote user name in the host name
.Ns ( Va user@host Ns
). You can also set ssh options by defining the
.Ev NIX_SSHOPTS
environment variable.
.
.It Fl -target-host Ar host
Specifies the NixOS target host. By setting this to something other than an
empty string, the system activation will happen on the remote host instead of
the local machine. The remote host needs to be accessible over
.Ic ssh Ns ,
and for the commands
.Cm switch Ns
,
.Cm boot
and
.Cm test
you need root access.
.Pp
If
.Fl -build-host
is not explicitly specified or empty, building will take place locally.
.Pp
You can include a remote user name in the host name
.Ns ( Va user@host Ns
). You can also set ssh options by defining the
.Ev NIX_SSHOPTS
environment variable.
.Pp
Note that
.Nm
honors the
.Va nixpkgs.crossSystem
setting of the given configuration but disregards the true architecture of the
target host. Hence the
.Va nixpkgs.crossSystem
setting has to match the target platform or else activation will fail.
.
.It Fl -use-substitutes
When set, nixos-rebuild will add
.Fl -use-substitutes
to each invocation of nix-copy-closure. This will only affect the behavior of
nixos-rebuild if
.Fl -target-host
or
.Fl -build-host
is also set. This is useful when the target-host connection to cache.nixos.org
is faster than the connection between hosts.
.
.It Fl -use-remote-sudo
When set, nixos-rebuild prefixes remote commands that run on the
.Fl -build-host
and
.Fl -target-host
systems with
.Ic sudo Ns
\&. Setting this option allows deploying as a non-root user.
.
.It Fl -flake Va flake-uri Ns Op Va #name
Build the NixOS system from the specified flake. It defaults to the directory
containing the target of the symlink
.Pa /etc/nixos/flake.nix Ns
, if it exists. The flake must contain an output named
.Ql nixosConfigurations. Ns Va name Ns
\&. If
.Va name
is omitted, it default to the current host name.
.
.It Fl -no-flake
Do not imply
.Fl -flake
if
.Pa /etc/nixos/flake.nix
exists. With this option, it is possible to build non-flake NixOS configurations
even if the current NixOS systems uses flakes.
.El
.Pp
In addition,
.Nm
accepts various Nix-related flags, including
.Fl -max-jobs Ns ,
.Fl j Ns ,
.Fl I Ns ,
.Fl -show-trace Ns ,
.Fl -keep-failed Ns ,
.Fl -keep-going Ns ,
.Fl -impure Ns ,
.Fl -verbose Ns , and
.Fl v Ns
\&. See the Nix manual for details.
.
.
.
.Sh ENVIRONMENT
.Bl -tag -width indent
.It Ev NIXOS_CONFIG
Path to the main NixOS configuration module. Defaults to
.Pa /etc/nixos/configuration.nix Ns
\&.
.
.It Ev NIX_PATH
A colon-separated list of directories used to look up Nix expressions enclosed
in angle brackets (e.g. <nixpkgs>). Example:
.Bd -literal -offset indent
nixpkgs=./my-nixpkgs
.Ed
.
.It Ev NIX_SSHOPTS
Additional options to be passed to
.Ic ssh
on the command line.
.Ed
.
.It Ev NIXOS_SWITCH_USE_DIRTY_ENV
Expose the the current environment variables to post activation scripts. Will
skip usage of
.Ic systemd-run
during system activation. Possibly dangerous, specially in remote environments
(e.g.: via SSH). Will be removed in the future.
.El
.
.
.
.Sh FILES
.Bl -tag -width indent
.It Pa /etc/nixos/flake.nix
If this file exists, then
.Nm
will use it as if the
.Fl -flake
option was given. This file may be a symlink to a
.Pa flake.nix
in an actual flake; thus
.Pa /etc/nixos
need not be a flake.
.
.It Pa /run/current-system
A symlink to the currently active system configuration in the Nix store.
.
.It Pa /nix/var/nix/profiles/system
The Nix profile that contains the current and previous system
configurations. Used to generate the GRUB boot menu.
.El
.
.
.
.Sh BUGS
This command should be renamed to something more descriptive.
.
.
.
.Sh AUTHORS
.An -nosplit
.An Eelco Dolstra
and
.An the Nixpkgs/NixOS contributors