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<?xml version="1.0"?>
<!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="systemd-backlight@.service" conditional='ENABLE_BACKLIGHT'>
<refentryinfo>
<title>systemd-backlight@.service</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-backlight@.service</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-backlight@.service</refname>
<refname>systemd-backlight</refname>
<refpurpose>Load and save the display backlight brightness at boot and shutdown</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>systemd-backlight@.service</filename></para>
<para><filename>/usr/lib/systemd/systemd-backlight</filename> save [backlight|leds]:DEVICE</para>
<para><filename>/usr/lib/systemd/systemd-backlight</filename> load [backlight|leds]:DEVICE</para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-backlight@.service</filename> is a service
that restores the display backlight brightness at early boot and
saves it at shutdown. On disk, the backlight brightness is stored
in <filename>/var/lib/systemd/backlight/</filename>. During
loading, if the udev property <option>ID_BACKLIGHT_CLAMP</option> is
not set to false, the brightness is clamped to a value of at
least 1 or 5% of maximum brightness, whichever is greater. This
restriction will be removed when the kernel allows user space to
reliably set a brightness value which does not turn off the
display.</para>
</refsect1>
<refsect1>
<title>Kernel Command Line</title>
<para><filename>systemd-backlight</filename> understands the
following kernel command line parameter:</para>
<variablelist class='kernel-commandline-options'>
<varlistentry>
<term><varname>systemd.restore_state=</varname></term>
<listitem><para>Takes a boolean argument. Defaults to
<literal>1</literal>. If <literal>0</literal>, does not
restore the backlight settings on boot. However, settings will
still be stored on shutdown. </para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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