<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-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>
    <arg>
      <option>-I</option>
      <replaceable>path</replaceable>
    </arg>
    <arg><option>--verbose</option></arg>
    <arg><option>--xml</option></arg>
    <arg choice="plain"><replaceable>option.name</replaceable></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.</para>

<para>When the option name is not an option, the command prints the list of
attributes contained in the attribute set.</para>

</refsection>

<refsection><title>Options</title>

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

<variablelist>

  <varlistentry>
    <term><option>-I</option> <replaceable>path</replaceable></term>
    <listitem>
      <para>
        This option is passed to the underlying
        <command>nix-instantiate</command> invocation.
      </para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>--verbose</option></term>
    <listitem>
      <para>
        This option enables verbose mode, which currently is just
        the Bash <command>set</command> <option>-x</option> debug mode.
      </para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>--xml</option></term>
    <listitem>
      <para>
        This option causes the output to be rendered as XML.
      </para>
    </listitem>
  </varlistentry>

</variablelist>

</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>Examples</title>

<para>Investigate option values:

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

$ nixos-option boot.loader.grub.enable
Value:
true

Default:
true

Description:
Whether to enable the GNU GRUB boot loader.

Declared by:
  "/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/nixos/modules/system/boot/loader/grub/grub.nix"

Defined by:
  "/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/nixos/modules/system/boot/loader/grub/grub.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>


</refentry>