man/systemd-backlight@.service.xml

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   2 <!--*-nxml-*-->
   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-or-later -->
   6 <refentry id="systemd-backlight@.service" conditional='ENABLE_BACKLIGHT'>
   7
   8   <refentryinfo>
   9     <title>systemd-backlight@.service</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd-backlight@.service</refentrytitle>
  15     <manvolnum>8</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  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>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <para><filename>systemd-backlight@.service</filename></para>
  26     <para><filename>/usr/lib/systemd/systemd-backlight</filename> save [backlight|leds]:DEVICE</para>
  27     <para><filename>/usr/lib/systemd/systemd-backlight</filename> load [backlight|leds]:DEVICE</para>
  28   </refsynopsisdiv>
  29
  30   <refsect1>
  31     <title>Description</title>
  32
  33     <para><filename>systemd-backlight@.service</filename> is a service
  34     that restores the display backlight brightness at early boot and
  35     saves it at shutdown. On disk, the backlight brightness is stored
  36     in <filename>/var/lib/systemd/backlight/</filename>. During
  37     loading, if the udev property <option>ID_BACKLIGHT_CLAMP</option> is
  38     not set to false, the brightness is clamped to a value of at
  39     least 1 or 5% of maximum brightness, whichever is greater. This
  40     restriction will be removed when the kernel allows user space to
  41     reliably set a brightness value which does not turn off the
  42     display.</para>
  43   </refsect1>
  44
  45   <refsect1>
  46     <title>Kernel Command Line</title>
  47
  48     <para><filename>systemd-backlight</filename> understands the
  49     following kernel command line parameter:</para>
  50
  51     <variablelist class='kernel-commandline-options'>
  52       <varlistentry>
  53         <term><varname>systemd.restore_state=</varname></term>
  54
  55         <listitem><para>Takes a boolean argument. Defaults to
  56         <literal>1</literal>. If <literal>0</literal>, does not
  57         restore the backlight settings on boot. However, settings will
  58         still be stored on shutdown. </para></listitem>
  59       </varlistentry>
  60     </variablelist>
  61   </refsect1>
  62
  63   <refsect1>
  64     <title>See Also</title>
  65     <para>
  66       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  67     </para>
  68   </refsect1>
  69
  70 </refentry>