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1 | <?xml version="1.0"?> |
2 | <!--*-nxml-*--> | |
3a54a157 | 3 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
eea10b26 | 4 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> |
db9ecf05 | 5 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
c101b656 | 6 | <refentry id="systemd-backlight_.service" conditional='ENABLE_BACKLIGHT' |
4623eecb | 7 | xmlns:xi="http://www.w3.org/2001/XInclude"> |
38e19f93 | 8 | |
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9 | <refentryinfo> |
10 | <title>systemd-backlight@.service</title> | |
11 | <productname>systemd</productname> | |
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12 | </refentryinfo> |
13 | ||
14 | <refmeta> | |
15 | <refentrytitle>systemd-backlight@.service</refentrytitle> | |
16 | <manvolnum>8</manvolnum> | |
17 | </refmeta> | |
18 | ||
19 | <refnamediv> | |
20 | <refname>systemd-backlight@.service</refname> | |
21 | <refname>systemd-backlight</refname> | |
22 | <refpurpose>Load and save the display backlight brightness at boot and shutdown</refpurpose> | |
23 | </refnamediv> | |
24 | ||
25 | <refsynopsisdiv> | |
26 | <para><filename>systemd-backlight@.service</filename></para> | |
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27 | <para><filename>/usr/lib/systemd/systemd-backlight</filename> save [backlight|leds]:DEVICE</para> |
28 | <para><filename>/usr/lib/systemd/systemd-backlight</filename> load [backlight|leds]:DEVICE</para> | |
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29 | </refsynopsisdiv> |
30 | ||
31 | <refsect1> | |
32 | <title>Description</title> | |
33 | ||
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34 | <para><filename>systemd-backlight@.service</filename> is a service that restores the brightness of |
35 | a display backlight or LED (e.g. keyboard backlight) device at early boot, and saves it at shutdown. | |
36 | The brightness is stored in <filename>/var/lib/systemd/backlight/</filename>.</para> | |
37 | ||
38 | <para>On restoring brightness of a display backlight device, <command>systemd-backlight</command> reads | |
39 | <varname>ID_BACKLIGHT_CLAMP</varname> udev property, that takes a boolean value or a percentage (needs to | |
40 | be suffixed with <literal>%</literal>, e.g. <literal>30%</literal>). When a percentage is specified, the | |
41 | saved brightness is clamped to a value of at least 1 or the specified percentage of the maximum | |
42 | brightness, whichever is greater. When unset or set to true, the brightness is clamped in the same way | |
43 | with percentage 5%. When false, the saved brightness will not be clamped, and loaded as is.</para> | |
44 | ||
45 | <para>On restoring brightness of a LED device, <command>systemd-backlight</command> reads | |
46 | <varname>ID_LEDS_CLAMP</varname> udev property, that also takes a boolean value or a percentage. When a | |
47 | percentage is specified, the saved brightness is clamped to the specified percentage of the maximum | |
48 | brightness. When set to true, the brightness is clamped in the same way with percentage 5%. When unset or | |
49 | set to false, the saved brightness will not be clamped, and loaded as is.</para> | |
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50 | </refsect1> |
51 | ||
52 | <refsect1> | |
53 | <title>Kernel Command Line</title> | |
54 | ||
55 | <para><filename>systemd-backlight</filename> understands the | |
56 | following kernel command line parameter:</para> | |
57 | ||
58 | <variablelist class='kernel-commandline-options'> | |
59 | <varlistentry> | |
60 | <term><varname>systemd.restore_state=</varname></term> | |
61 | ||
62 | <listitem><para>Takes a boolean argument. Defaults to | |
63 | <literal>1</literal>. If <literal>0</literal>, does not | |
64 | restore the backlight settings on boot. However, settings will | |
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65 | still be stored on shutdown. </para> |
66 | ||
67 | <xi:include href="version-info.xml" xpointer="v209"/></listitem> | |
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68 | </varlistentry> |
69 | </variablelist> | |
70 | </refsect1> | |
71 | ||
72 | <refsect1> | |
73 | <title>See Also</title> | |
74 | <para> | |
75 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
76 | </para> | |
77 | </refsect1> | |
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78 | |
79 | </refentry> |