When I installed Ubuntu on my current machine, Dell XPS15 2020, I could not
control the amount of backlight on my screen with the keyboard shortcuts. For a
while I was using Xorg still, and
xrandr worked fine. Since this weekend I’m
trying Wayland again, so
xrandr wasn’t an option anymore. Time to debug!
ls -al /sys/class/backlight/ I noticed there were multiple entries
symlinked, while I expected one. There was both a
intell_backlight. Following the former, I noticed that pressing the hotkeys to
change the brightness changed the
dell_backlight/brightness file contents.
It seems the kernel was prioritizing the dell backlight over the intel one,
which I hoped would be fixed by adding
acpi_backlight=intel as kernel
/etc/default/grub and executing
update-grub. But, it didn’t.
What I did notice is that the
dell_backlight directory symlink was gone from
Browsing some more there were more Kernel params to try:
None of these worked, and I was on the wrong track.
After a series of reboots, and back to square 1 I ran:
sudo -i && echo 1000 > /sys/class/backlight/intell_backlight/brightness which
did change the value in the file, but didn’t change the brigntness. That gave me
new ideas to try, and after a while I found a repository with a python script
github.com/idifuchs/icc-brightness. Running it had effect, changing the
intel_backlight/brightness value changed the actual screen brightness. Given
it was fairy late already in my day, for now I don’t know what this code does,
and why it didn’t work out of the box for Ubuntu. That’s for another day to