3 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
5 SPDX-License-Identifier: LGPL-2.1+
7 This file is part of systemd.
9 Copyright 2013 Lennart Poettering
11 <refentry id=
"systemd-backlight@.service" conditional='ENABLE_BACKLIGHT'
>
14 <title>systemd-backlight@.service
</title>
15 <productname>systemd
</productname>
19 <contrib>Developer
</contrib>
20 <firstname>Lennart
</firstname>
21 <surname>Poettering
</surname>
22 <email>lennart@poettering.net
</email>
28 <refentrytitle>systemd-backlight@.service
</refentrytitle>
29 <manvolnum>8</manvolnum>
33 <refname>systemd-backlight@.service
</refname>
34 <refname>systemd-backlight
</refname>
35 <refpurpose>Load and save the display backlight brightness at boot and shutdown
</refpurpose>
39 <para><filename>systemd-backlight@.service
</filename></para>
40 <para><filename>/usr/lib/systemd/systemd-backlight
</filename></para>
44 <title>Description
</title>
46 <para><filename>systemd-backlight@.service
</filename> is a service
47 that restores the display backlight brightness at early boot and
48 saves it at shutdown. On disk, the backlight brightness is stored
49 in
<filename>/var/lib/systemd/backlight/
</filename>. During
50 loading, if the udev property
<option>ID_BACKLIGHT_CLAMP
</option> is
51 not set to false, the brightness is clamped to a value of at
52 least
1 or
5% of maximum brightness, whichever is greater. This
53 restriction will be removed when the kernel allows user space to
54 reliably set a brightness value which does not turn off the
59 <title>Kernel Command Line
</title>
61 <para><filename>systemd-backlight
</filename> understands the
62 following kernel command line parameter:
</para>
64 <variablelist class='kernel-commandline-options'
>
66 <term><varname>systemd.restore_state=
</varname></term>
68 <listitem><para>Takes a boolean argument. Defaults to
69 <literal>1</literal>. If
<literal>0</literal>, does not
70 restore the backlight settings on boot. However, settings will
71 still be stored on shutdown.
</para></listitem>
77 <title>See Also
</title>
79 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>