3 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
4 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
5 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
6 <refentry id=
"systemd-backlight@.service" conditional='ENABLE_BACKLIGHT'
>
9 <title>systemd-backlight@.service
</title>
10 <productname>systemd
</productname>
14 <refentrytitle>systemd-backlight@.service
</refentrytitle>
15 <manvolnum>8</manvolnum>
19 <refname>systemd-backlight@.service
</refname>
20 <refname>systemd-backlight
</refname>
21 <refpurpose>Load and save the display backlight brightness at boot and shutdown
</refpurpose>
25 <para><filename>systemd-backlight@.service
</filename></para>
26 <para><filename>/usr/lib/systemd/systemd-backlight
</filename></para>
30 <title>Description
</title>
32 <para><filename>systemd-backlight@.service
</filename> is a service
33 that restores the display backlight brightness at early boot and
34 saves it at shutdown. On disk, the backlight brightness is stored
35 in
<filename>/var/lib/systemd/backlight/
</filename>. During
36 loading, if the udev property
<option>ID_BACKLIGHT_CLAMP
</option> is
37 not set to false, the brightness is clamped to a value of at
38 least
1 or
5% of maximum brightness, whichever is greater. This
39 restriction will be removed when the kernel allows user space to
40 reliably set a brightness value which does not turn off the
45 <title>Kernel Command Line
</title>
47 <para><filename>systemd-backlight
</filename> understands the
48 following kernel command line parameter:
</para>
50 <variablelist class='kernel-commandline-options'
>
52 <term><varname>systemd.restore_state=
</varname></term>
54 <listitem><para>Takes a boolean argument. Defaults to
55 <literal>1</literal>. If
<literal>0</literal>, does not
56 restore the backlight settings on boot. However, settings will
57 still be stored on shutdown.
</para></listitem>
63 <title>See Also
</title>
65 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>