Brightness Key on Linux

Problem

One can use xrandr to adjust screen brightness. However, the factor (default to 1.0) is relative to the current brightness. How to enable the brightness adjust keys / on the keyboard under Xubuntu 18.04?

Solution

Toz’s post on Ubuntu Forum works like a charm. The default value for GRUB_CMDLINE_LINUX is an empty string. Changing it to acpi_backlight=vendor and updating the GRUB has solved the problem since the next boot.

Remarks

Unfortunately, the thread is now closed, so I can’t leave a comment to remind myself of this useful post. Therefore, I’ve written this post.