38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering<!--*-nxml-*-->
12b42c76672a66c2d4ea7212c14f8f1b5a62b78dTom Gundersen<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering This file is part of systemd.
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering Copyright 2013 Lennart Poettering
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering systemd is free software; you can redistribute it and/or modify it
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering under the terms of the GNU Lesser General Public License as published by
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering the Free Software Foundation; either version 2.1 of the License, or
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering (at your option) any later version.
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering systemd is distributed in the hope that it will be useful, but
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering WITHOUT ANY WARRANTY; without even the implied warranty of
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering Lesser General Public License for more details.
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering You should have received a copy of the GNU Lesser General Public License
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering along with systemd; If not, see <http://www.gnu.org/licenses/>.
38e19f93501d5a23d2176be30eea82e1be999f3dLennart Poettering<refentry id="systemd-backlight@.service" conditional='ENABLE_BACKLIGHT'>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <title>systemd-backlight@.service</title>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <productname>systemd</productname>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <email>lennart@poettering.net</email>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <refentrytitle>systemd-backlight@.service</refentrytitle>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <refname>systemd-backlight@.service</refname>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <refname>systemd-backlight</refname>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <refpurpose>Load and save the display backlight brightness at boot and shutdown</refpurpose>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <refsynopsisdiv>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <para><filename>systemd-backlight@.service</filename></para>
12b42c76672a66c2d4ea7212c14f8f1b5a62b78dTom Gundersen <para><filename>/usr/lib/systemd/systemd-backlight</filename></para>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek </refsynopsisdiv>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <para><filename>systemd-backlight@.service</filename> is a service
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek that restores the display backlight brightness at early boot and
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek saves it at shutdown. On disk, the backlight brightness is stored
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek in <filename>/var/lib/systemd/backlight/</filename>. During
a8eaaee72a2f06e0fb64fb71de3b71ecba31dafbJan Engelhardt loading, if the udev property <option>ID_BACKLIGHT_CLAMP</option> is
a8eaaee72a2f06e0fb64fb71de3b71ecba31dafbJan Engelhardt not set to false, the brightness is clamped to a value of at
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek least 1 or 5% of maximum brightness, whichever is greater. This
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek restriction will be removed when the kernel allows user space to
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek reliably set a brightness value which does not turn off the
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <title>Kernel Command Line</title>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <para><filename>systemd-backlight</filename> understands the
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek following kernel command line parameter:</para>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <variablelist class='kernel-commandline-options'>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <term><varname>systemd.restore_state=</varname></term>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <listitem><para>Takes a boolean argument. Defaults to
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <literal>1</literal>. If <literal>0</literal>, does not
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek restore the backlight settings on boot. However, settings will
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek still be stored on shutdown. </para></listitem>
798d3a524ea57aaf40cb53858aaa45ec702f012dZbigniew Jędrzejewski-Szmek <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>