[Linux] Backlight not controllable – fix (Samsung Series 7 Chronos)

I’ve had some difficulties when it came to the backlight on my arch linux installation.
Of course the first place to look for a solution was the arch wiki but I couldn’t find the right combination of kernel params to brighten the screen. It was kind of dark and the other possible mode was completely off.
After searching for a while I found a bug report having the same problem as I had so I had a look at it and checked to see if this works. My expectation was low given the fact that I thought that I’ve already tried everything but fortunately this helped.

The Fix:

1. Getting the correct backlight files:

• Edit /etc/default/grub with your favorite text editor
• Go to the line starting with GRUB_CMDLINE_LINUX_DEFAULT
• Append acpi_osi=linux acpi_backlight=video
• execute sudo update-grub

2. a) Controlling the backlight with the keys

While this didn’t work for me I still list it in case it works for anyone else. Found the snippet below here. It offers additional explanation but even though I checked the values and they seemed to be correct for me aswell it didn’t work and I gave up after two hours of trial and error.

#/usr/share/X11/xorg.conf.d/20-intel.conf 
Section "Device"
     Identifier "Intel Graphics"
     Driver "i915"
     Option "AccelMethod" "sna"
     Option "Backlight" "acpi_video0"
     BusID "PCI:0:2:0"
 EndSection

2. b) Controlling the backlight with a script

Now that we can simply write the brightness into a file we can create a quick script for setting the brightness so we don’t have to remember the path.

#!/bin/bash
sudo tee /sys/class/backlight/acpi_video0/brightness <<< $1

Execute the file with the desired brightness value. You can get the max brightness by executing the following command

sudo cat /sys/class/backlight/acpi_video0/max_brightness

If you managed to build a nice script that allows the user to change the brightness and map it to the keys then I would be more than happy if you could share it!