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<refentry xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refmeta>
<refentrytitle><command>nixos-rebuild</command></refentrytitle>
<manvolnum>8</manvolnum>
<refmiscinfo class="source">NixOS</refmiscinfo>
<!-- <refmiscinfo class="version"><xi:include href="version.txt" parse="text"/></refmiscinfo> -->
</refmeta>
<refnamediv>
<refname><command>nixos-rebuild</command></refname>
<refpurpose>reconfigure a NixOS machine</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>nixos-rebuild</command>
<group choice='req'>
<arg choice='plain'><option>switch</option></arg>
<arg choice='plain'><option>boot</option></arg>
<arg choice='plain'><option>test</option></arg>
<arg choice='plain'><option>build</option></arg>
<arg choice='plain'><option>dry-run</option></arg>
<arg choice='plain'><option>build-vm</option></arg>
<arg choice='plain'><option>build-vm-with-bootloader</option></arg>
</group>
<sbr />
<arg><option>--upgrade</option></arg>
<arg><option>--install-grub</option></arg>
<arg><option>--no-build-nix</option></arg>
<arg><option>--fast</option></arg>
<arg><option>--rollback</option></arg>
<sbr />
<arg><option>--show-trace</option></arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsection><title>Description</title>
<para>This command updates the system so that it corresponds to the
configuration specified in
<filename>/etc/nixos/configuration.nix</filename>. Thus, every time
you modify <filename>/etc/nixos/configuration.nix</filename> or any
NixOS module, you must run <command>nixos-rebuild</command> to make
the changes take effect. It builds the new system in
<filename>/nix/store</filename>, runs its activation script, and stop
and (re)starts any system services if needed.</para>
<para>This command has one required argument, which specifies the
desired operation. It must be one of the following:
<variablelist>
<varlistentry>
<term><option>switch</option></term>
<listitem>
<para>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 meny entry, so that subsequent reboots
will boot the system into the new configuration. Previous
configurations activated with <command>nixos-rebuild
switch</command> or <command>nixos-rebuild boot</command> remain
available in the GRUB menu.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>boot</option></term>
<listitem>
<para>Build the new configuration and make it the boot default
(as with <command>nixos-rebuild switch</command>), but do not
activate it. That is, the system continues to run the previous
configuration until the next reboot.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>test</option></term>
<listitem>
<para>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 <command>nixos-rebuild switch</command> or
<command>nixos-rebuild boot</command>).</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>build</option></term>
<listitem>
<para>Build the new configuration, but neither activate it nor
add it to the GRUB boot menu. It leaves a symlink named
<filename>result</filename> in the current directory, which
points to the output of the top-level “system” derivation. This
is essentially the same as doing
<screen>
$ nix-build /etc/nixos/nixos -A system
</screen>
Note that you do not need to be <literal>root</literal> to run
<command>nixos-rebuild build</command>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>dry-run</option></term>
<listitem>
<para>Simply show what store paths would be built or downloaded
by any of the operations above.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>build-vm</option></term>
<listitem>
<para>Build a script that starts a NixOS virtual machine with
the desired configuration. It leaves a symlink
<filename>result</filename> in the current directory that points
(under
<filename>result/bin/run-<replaceable>hostname</replaceable>-vm</filename>)
at the script that starts the VM. Thus, to test a NixOS
configuration in a virtual machine, you should do the following:
<screen>
$ nixos-rebuild build-vm
$ ./result/bin/run-*-vm
</screen></para>
<para>The VM is implemented using the <literal>qemu</literal>
package. For best performance, you should load the
<literal>kvm-intel</literal> or <literal>kvm-amd</literal>
kernel modules to get hardware virtualisation.</para>
<para>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 <command>nixos-rebuild</command>; to
change the VM’s configuration, you must halt the VM and re-run
the commands above.
</para>
<para>The VM has its own <literal>ext3</literal> 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
<literal>./<replaceable>hostname</replaceable>.qcow2</literal>.
<!-- The entire file system hierarchy of the host is available in
the VM under <filename>/hostfs</filename>.--></para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>build-vm-with-bootloader</option></term>
<listitem>
<para>Like <option>build-vm</option>, 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 <command>nixos-rebuild switch</command>), 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 <filename>/boot</filename>
partition, which is mounted read-only in the VM.</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsection>
<refsection><title>Options</title>
<para>This command accepts the following options:</para>
<variablelist>
<varlistentry>
<term><option>--upgrade</option></term>
<listitem>
<para>Fetch the latest version of NixOS from the NixOS
channel.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--install-grub</option></term>
<listitem>
<para>Causes the GRUB boot loader to be (re)installed on the
device specified by the
<varname>boot.loader.grub.device</varname> configuration
option.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--no-build-nix</option></term>
<listitem>
<para>Normally, <command>nixos-rebuild</command> first builds
the <varname>nixUnstable</varname> 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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--fast</option></term>
<listitem>
<para>Equivalent to <option>--no-build-nix</option>
<option>--show-trace</option>. This option is useful if you
call <command>nixos-rebuild</command> frequently (e.g. if you’re
hacking on a NixOS module).</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--rollback</option></term>
<listitem>
<para>Instead of building a new configuration as specified by
<filename>/etc/nixos/configuration.nix</filename>, roll back to
the previous configuration. (The previous configuration is
defined as the one before the “current” generation of the
profile <filename>/nix/var/nix/profiles/system</filename>.)</para>
</listitem>
</varlistentry>
</variablelist>
<para>In addition, <command>nixos-rebuild</command> accepts various
Nix-related flags, including <option>--max-jobs</option> /
<option>-j</option>, <option>--show-trace</option>,
<option>--keep-failed</option>, <option>--keep-going</option> and
<option>--verbose</option> / <option>-v</option>. See
the Nix manual for details.</para>
</refsection>
<refsection><title>Environment</title>
<variablelist>
<varlistentry>
<term><envar>NIXOS_CONFIG</envar></term>
<listitem>
<para>Path to the main NixOS configuration module. Defaults to
<filename>/etc/nixos/configuration.nix</filename>.</para>
</listitem>
</varlistentry>
</variablelist>
</refsection>
<refsection><title>Files</title>
<variablelist>
<varlistentry>
<term><filename>/run/current-system</filename></term>
<listitem>
<para>A symlink to the currently active system configuration in
the Nix store.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><filename>/nix/var/nix/profiles/system</filename></term>
<listitem>
<para>The Nix profile that contains the current and previous
system configurations. Used to generate the GRUB boot
menu.</para>
</listitem>
</varlistentry>
</variablelist>
</refsection>
<refsection><title>Bugs</title>
<para>This command should be renamed to something more
descriptive.</para>
</refsection>
</refentry>