[System] Solving a KDE Plasma power management / PowerDevil configuration bug…

[Schwarzer Kater]

I am currently trying to solve a KDE Plasma power management / PowerDevil configuration bug in Kubuntu 26.04 LTS.


Here it is, as an excerpt from sudo journalctl -b -p3:

[…]
org_kde_powerdevil[2931]: [ 2931] Error(s) opening ddc devices
[…]
org_kde_powerdevil[2931]: [ 2931] Error EACCES(-13): Permission denied opening /dev/i2c-4
org_kde_powerdevil[2931]: [ 2931] Error EACCES(-13): Permission denied opening /dev/i2c-5
[…]
org_kde_powerdevil[2931]: [ 2931] Error EACCES(-13): Permission denied opening /dev/i2c-8
[…]

In lack of a better idea I have tried to solve this by adding a udev rule in /etc/udev/rules.d/ …


Why doesn't this udev rule work?

SUBSYSTEM=="i2c-dev", KERNEL=="i2c-[0-9]*", TAG+="uaccess"
(which I would prefer over the following one)


This udev rule works…

SUBSYSTEM=="i2c-dev", KERNEL=="i2c-[0-9]*", MODE="0660", GROUP="users"
(after I had manually added the user originally created during installation to the users group with
sudo usermod -aG users $USER
- all subsequently created users are automatically added to the users group anyway…)

Afterwards (and after a reboot, of course) I was able to e.g. set a time for "Dim automatically:" in
-> System Settings -> Power Management (section: System) -> Display and Brightness


Any ideas why the first rule did not work or how the permission configuration for KDE PowerDevil / i2c-devs could be handled better?