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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-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>-v</option>
<option>-d</option>
<option>-l</option>
</group>
<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. By default, it returns the value of
the option.</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>--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>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 information:
<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:
/path/to/nixpkgs/nixos/modules/system/boot/kernel.nix
/path/to/nixpkgs/nixos/modules/hardware/network/rt73.nix
/path/to/nixpkgs/nixos/modules/hardware/network/intel-3945abg.nix
/path/to/nixpkgs/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>
</refentry>