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[INFO] Set your brightness via terminal

Posted: Thu Jul 26, 2018 8:37 am
by UOOP
During a big set of updates vie pksyua my screen went dark as it should have via power management control due to being idle, but failed to brighten again once active. The following commands, for me, failed to increase or decrease the brightness:

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xbacklight -inc 100

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xbacklight -dec 25

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xbacklight -set 80
xbacklight did not return an error, but failed to change my display's backlight. Performing a logout and a reboot failed to change the backlight brightness. After some time on Google, I was able to find a solution found here:

http://www.pclinuxos.com/forum/index.php?topic=99190.0

Quoted text from the above URL:
ACPI

It is often possible to adjust the backlight by ACPI. This controls the actual LEDs or cathodes of the screen. When this ACPI option is available, the illumination is controllable using a GUI slider in the Display/Screen system settings or by simple commands on the CLI.

Different cards might manage this differently. Check /sys/class/backlight to find out:

# ls /sys/class/backlight/

intel_backlight

So this particular backlight is managed by an Intel card. It is called acpi_video0 on an ATI card. In the following example, acpi_video0 is used.

The directory contains the following files and folders:

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

The maximum brightness (often 15) can be found by running cat:

# cat /sys/class/backlight/acpi_video0/max_brightness
15

Brightness can then be set (as root) with echo. Obviously you cannot go any higher than your screen's maximum brightness. The values for maximum brightness and brightness in general vary wildly among cards.

# echo 5 > /sys/class/backlight/acpi_video0/brightness
The solution that solved my problem:

1.

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cd /sys/class/backlight
2.

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ls
acpi_video0 nv_backlight

3.

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cd acpi_video0
4.

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ls
actual_brightness brightness max_brightness subsystem uevent bl_power device power type

5.

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 cat max_brightness
8

6.

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su
enter password

7.

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echo 8 > brightness
8. My display brightened up after code execution and I did not need a reboot or a logout/login

This isn't the first time i have had issues with my backlight after updates. The first time I resolved the issue was with a clean install of the latest Arcolinux ISO, but I wanted a different solution this time.

I hope this helps :) :)

Re: [INFO] Set your brightness via terminal

Posted: Fri Jul 27, 2018 3:39 am
by darknetmatrix
great tip, tnx. for it!

Re: [INFO] Set your brightness via terminal

Posted: Fri Jul 27, 2018 9:49 am
by UOOP
darknetmatrix wrote:
Fri Jul 27, 2018 3:39 am
great tip, tnx. for it!
No problem :) I was beating my head against the wall for a week trying to figure this out ha ha :)