<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-build</option></arg>
      <arg choice='plain'><option>dry-activate</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>
      <group choice='req'>
        <arg choice='plain'><option>--profile-name</option></arg>
        <arg choice='plain'><option>-p</option></arg>
      </group>
      <replaceable>name</replaceable>
    </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 /path/to/nixpkgs/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-build</option></term>
    <listitem>
      <para>Show what store paths would be built or downloaded by any
      of the operations above, but otherwise do nothing.</para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>dry-activate</option></term>
    <listitem>
      <para>Build the new configuration, but instead of activating it,
      show what changes would be performed by the activation (i.e. by
      <command>nixos-rebuild test</command>). For
      instance, this command will print which systemd units would be
      restarted. The list of changes is not guaranteed to be
      complete.</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
      Nix profile <filename>/nix/var/nix/profiles/system</filename>.)</para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>--profile-name</option></term>
    <term><option>-p</option></term>
    <listitem>
      <para>Instead of using the Nix profile
      <filename>/nix/var/nix/profiles/system</filename> to keep track
      of the current and previous system configurations, use
      <filename>/nix/var/nix/profiles/system-profiles/<replaceable>name</replaceable></filename>.
      When you use GRUB 2, for every system profile created with this
      flag, NixOS will create a submenu named “NixOS - Profile
      '<replaceable>name</replaceable>'” in GRUB’s boot menu,
      containing the current and previous configurations of this
      profile.</para>

      <para>For instance, if you want to test a configuration file
      named <filename>test.nix</filename> without affecting the
      default system profile, you would do:

<screen>
$ nixos-rebuild switch -p test -I nixos-config=./test.nix
</screen>

      The new configuration will appear in the GRUB 2 submenu “NixOS - Profile
      'test'”.</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>
