systemd/man/systemd-backlight@.service.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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<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></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>