nixpkgs/doc/manual/man-nixos-option.xml

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          xmlns:xlink="http://www.w3.org/1999/xlink"
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<refmeta>
  <refentrytitle><command>nixos-option</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-option</command></refname>
  <refpurpose>inspect a NixOS configuration</refpurpose>
</refnamediv>

<refsynopsisdiv>
  <cmdsynopsis>
    <command>nixos-option</command>
    <group choice="opt">
      <option>-i</option>
      <option>v</option>
      <option>d</option>
      <option>l</option>
    </group>
    <arg choice='plain'><replaceable>option.name</replaceable></arg>
  </cmdsynopsis>
  <cmdsynopsis>
    <command>nixos-option</command>
    <arg choice='plain'><option>--install</option></arg>
  </cmdsynopsis>
</refsynopsisdiv>


<refsection><title>Description</title>

<para>This command evaluates the configuration specified in
<filename>/etc/nixos/configuration.nix</filename> and returns the properties
of the option name given as argument.  By default, it returns the value of
the option.</para>

<para>When the option name is not an option prints the list of attributes in
case of an attribute set.  This could used to provide completion in some
editors.</para>

<para>When the option <option>--install</option> (or <option>-i</option>) is
used with no option name, this command generates a template configuration
with a scan of the target system.  It produces a template configuration
in <filename>/etc/nixos/configuration.nix</filename>, and a scan of the
machine in <filename>/etc/nixos/hardware-configuration.nix</filename>.  The
scan of the machine is produced
by <command>nixos-hardware-scan</command>.</para>

</refsection>

<refsection><title>Options</title>

<para>This command accepts the following options:</para>

<variablelist>

  <varlistentry>
    <term><option>--install</option>, <option>-i</option></term>
    <listitem>
      <para>Use the installation configuration instead of current system
      configuration.  Generate a template configuration if no option name is
      specified.</para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>--value</option>, <option>-v</option></term>
    <listitem>
      <para>Returns the value of the option.  This is the default operation
      if no other options are defined.</para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>--description</option>, <option>-d</option></term>
    <listitem>
      <para>Return the default value, the example and the description of the
      option when available.</para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>--lookup</option>, <option>-l</option></term>
    <listitem>
      <para>Return the locations where the option is declared and where it
      is defined.  This is extremely useful to find sources of errors in
      your configuration.</para>
    </listitem>
  </varlistentry>

</variablelist>

</refsection>


<refsection><title>Environment</title>

<variablelist>

  <varlistentry>
    <term><envar>mountPoint</envar></term>
    <listitem>
      <para>Location of the target file system.  Defaults to
      <filename>/mnt</filename>.  This environment variable is only used in
      combinaison with <option>--install</option> option.</para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><envar>NIXOS</envar></term>
    <listitem>
      <para>Path to the NixOS source tree.  Defaults to
      <filename>/etc/nixos/nixos</filename>.</para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><envar>NIXPKGS</envar></term>
    <listitem>
      <para>Path to the Nixpkgs source tree.  Defaults to
      <filename>/etc/nixos/nixpkgs</filename>.</para>
    </listitem>
  </varlistentry>

  <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>Examples</title>

<para>Investigate option values:

<screen>$ nixos-option boot.loader
This attribute set contains:
generationsDir
grub
initScript

$ nixos-option boot.loader.grub.enable
true</screen></para>

<para>Prints option informations:

<screen>$ nixos-option -d networking.hostName
Default: "nixos"
Description:
The name of the machine. Leave it empty if you want to obtain
it from a DHCP server (if using DHCP).</screen></para>

<para>Find the locations which are declaring and defining an option:

<screen>$ nixos-option -l hardware.firmware
Declared by:
  /mnt/data/nix-sources/nixos/modules/services/hardware/udev.nix

Defined by:
  /etc/nixos/nixos/modules/system/boot/kernel.nix
  /etc/nixos/nixos/modules/hardware/network/rt73.nix
  /etc/nixos/nixos/modules/hardware/network/intel-3945abg.nix
  /etc/nixos/nixos/modules/hardware/network/intel-2200bg.nix</screen></para>

</refsection>

<refsection><title>Bugs</title>

<para>The author listed in the following section is wrong.  If there is any
  other bug, please report to Nicolas Pierron.</para>

</refsection>


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