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ArchLinux:Backlight

ArchLinux에서 모니터 밝기 설정 방법.

Hardware interfaces

ACPI

The brightness of the screen backlight is adjusted by setting the power level of the backlight LEDs or cathodes. The power level can often be controlled using the ACPI kernel module for video. An interface to this module is provided via a sysfs directory at /sys/class/backlight/.

The name of the directory depends on the graphics card model. 

ls /sys/class/backlight/

In this case, the backlight is managed by an ATI graphics card. In the case of an Intel card, the directory is called intel_backlight. In the following examples, acpi_video0 is used. If you use an Intel card, simply replace acpi_video0 with intel_backlight in the examples.

The directory contains the following files and subdirectories: 

ls /sys/class/backlight/acpi_video0/

actual_brightness  brightness         max_brightness     subsystem/    uevent             
bl_power           device/            power/             type

The maximum brightness can be displayed by reading from max_brightness, which is often 15. 

cat /sys/class/backlight/acpi_video0/max_brightness

15

The brightness can be set by writing a number to brightness. Attempting to set a brightness greater than the maximum results in an error. 

echo 5 > /sys/class/backlight/acpi_video0/brightness

By default, only root can change the brightness by this method. To allow users in the video group to change the brightness, a udev rule such as the following can be used: 

vi /etc/udev/rules.d/backlight.rules

ACTION=="add", SUBSYSTEM=="backlight", KERNEL=="acpi_video0", GROUP="video", MODE="0664"

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