systemd-backlight@.service, systemd-backlight - Load and save the display backlight brightness at boot

       systemd-backlight@.service is a service that restores the brightness of a display backlight or LED (e.g.
       keyboard backlight) device at early boot, and saves it at shutdown. The brightness is stored in
       /var/lib/systemd/backlight/.

       On restoring brightness of a display backlight device, systemd-backlight reads ID_BACKLIGHT_CLAMP udev
       property, that takes a boolean value or a percentage (needs to be suffixed with "%", e.g.  "30%"). When a
       percentage is specified, the saved brightness is clamped to a value of at least 1 or the specified
       percentage of the maximum brightness, whichever is greater. When unset or set to true, the brightness is
       clamped in the same way with percentage 5%. When false, the saved brightness will not be clamped, and
       loaded as is.

       On restoring brightness of a LED device, systemd-backlight reads ID_LEDS_CLAMP udev property, that also
       takes a boolean value or a percentage. When a percentage is specified, the saved brightness is clamped to
       the specified percentage of the maximum brightness. When set to true, the brightness is clamped in the
       same way with percentage 5%. When unset or set to false, the saved brightness will not be clamped, and
       loaded as is.

       systemd-backlight understands the following kernel command line parameter:

       systemd.restore_state=
           Takes a boolean argument. Defaults to "1". If "0", does not restore the backlight settings on boot.
           However, settings will still be stored on shutdown.

           Added in version 209.

       systemd-backlight@.service, systemd-backlight - Load and save the display backlight brightness at boot
       and shutdown

systemd(1)

systemd 257.4                                                                      SYSTEMD-BACKLIGHT@.SERVICE(8)

       systemd-backlight@.service

       /usr/lib/systemd/systemd-backlight save [backlight|leds]:DEVICE

       /usr/lib/systemd/systemd-backlight load [backlight|leds]:DEVICE