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80 lines
3.4 KiB
XML
80 lines
3.4 KiB
XML
<?xml version="1.0"?>
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<!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-backlight_.service" conditional='ENABLE_BACKLIGHT'
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd-backlight@.service</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-backlight@.service</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-backlight@.service</refname>
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<refname>systemd-backlight</refname>
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<refpurpose>Load and save the display backlight brightness at boot and shutdown</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-backlight@.service</filename></para>
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<para><filename>/usr/lib/systemd/systemd-backlight</filename> save [backlight|leds]:DEVICE</para>
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<para><filename>/usr/lib/systemd/systemd-backlight</filename> load [backlight|leds]:DEVICE</para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-backlight@.service</filename> is a service that restores the brightness of
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a display backlight or LED (e.g. keyboard backlight) device at early boot, and saves it at shutdown.
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The brightness is stored in <filename>/var/lib/systemd/backlight/</filename>.</para>
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<para>On restoring brightness of a display backlight device, <command>systemd-backlight</command> reads
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<varname>ID_BACKLIGHT_CLAMP</varname> udev property, that takes a boolean value or a percentage (needs to
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be suffixed with <literal>%</literal>, e.g. <literal>30%</literal>). When a percentage is specified, the
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saved brightness is clamped to a value of at least 1 or the specified percentage of the maximum
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brightness, whichever is greater. When unset or set to true, the brightness is clamped in the same way
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with percentage 5%. When false, the saved brightness will not be clamped, and loaded as is.</para>
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<para>On restoring brightness of a LED device, <command>systemd-backlight</command> reads
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<varname>ID_LEDS_CLAMP</varname> udev property, that also takes a boolean value or a percentage. When a
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percentage is specified, the saved brightness is clamped to the specified percentage of the maximum
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brightness. When set to true, the brightness is clamped in the same way with percentage 5%. When unset or
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set to false, the saved brightness will not be clamped, and loaded as is.</para>
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</refsect1>
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<refsect1>
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<title>Kernel Command Line</title>
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<para><filename>systemd-backlight</filename> understands the
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following kernel command line parameter:</para>
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<variablelist class='kernel-commandline-options'>
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<varlistentry>
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<term><varname>systemd.restore_state=</varname></term>
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<listitem><para>Takes a boolean argument. Defaults to
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<literal>1</literal>. If <literal>0</literal>, does not
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restore the backlight settings on boot. However, settings will
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still be stored on shutdown. </para>
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<xi:include href="version-info.xml" xpointer="v209"/></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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