Linux Backlight – Control Backlight as a User Without xbacklight

There are many ways to do this, but since it seems that your graphics card is made by Nvidia, I think the way which works best is the following (assuming you use nvidia-driver):

1. Create a file called 10-brightness.conf to /etc/X11/xorg.conf.d/

2. Write the following lines to the file you just created:

   Section "Device"
       Identifier     "Device0"
       Driver         "nvidia"
       Option         "RegistryDwords" "EnableBrightnessControl=1"
   EndSection
   

3. Now restart X (use pkill X to kill X, and then display manager should cause new instance of X to be spawned. If you don't have a display manager (such as GDM, KDM), then log in to virtual console and write startx) or reboot your computer, and then you should be able to adjust the brightness of backlight by hitting brightness keys.

Another way of doing it

This way should work with all graphics cards, and this is also some kind of fallback way if your brightness keys don't work.

Note: In the following commands, # states for root prompt, although you actually don't need root rights until the last point, and acpi_video0 is just placeholder for the actual card name, replace it with the name you will find in the point 1.

1. To find the card which manages the screen, run this command:

   # ls /sys/class/backlight/
   

   There should be only one entry, so it's the card.

2. To find the maximum brightness, run this command:

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

   This command often prints 15.

3. To adjust the brightness, run this command (as root, as stated previously):

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

   You can echo there any number you want, although the screen cannot be brighter than its maximum brightness, so if you echo higher number, say 50, there, the screen should just set its brightness to the maximum.

Sources

• Archlinux's wiki page about Nvidia propietary graphics card driver.
• Archlinux's wiki page about controlling screen brightness.

You could write your own pretty easily.

Create two shell scripts containing the echo lines above somewhere in your path (/usr/local is the normal place). Set the permissions 755 owned by root. Then either edit your sudoers file to allow them to be run as root, or use chmod +s to set them SUID.

This sort of thing is considered a security risk, BTW, so make absolutely sure the permissions are set appropriately. You don't want anyone without root permissions to be able to edit the scripts, and you don't want the scripts to use any input.

It would be trivial to add support for a brightness level flag, but unless you're an accomplished shell scripter I'd recommend against it as a bug in your code would be a security hole.