Bug 505832

Summary: Powerdevil: Error EACCES(-13): No permission opening /dev/i2c-*
Product: [Plasma] plasmashell Reporter: Marcus Seyfarth <m.seyfarth>
Component: Power management & brightnessAssignee: Plasma Bugs List <plasma-bugs-null>
Status: RESOLVED DOWNSTREAM    
Severity: minor CC: nate
Priority: NOR    
Version First Reported In: 6.3.5   
Target Milestone: 1.0   
Platform: Other   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description Marcus Seyfarth 2025-06-20 10:04:37 UTC 
SUMMARY
Looking through my journalctl logs, I’ve noticed these powerdevil-related errors when trying to access i2c for a while now:

Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: Initializing libddcutil. ddcutil version: 2.2.1-dev, shared library: /usr/lib/libddcutil.so.5.3.0 Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Options passed from client: Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Applying combined libddcutil options: Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Device /dev/i2c-0 lacks R/W permissions Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Device /dev/i2c-1 lacks R/W permissions Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Device /dev/i2c-2 lacks R/W permissions Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Device /dev/i2c-3 lacks R/W permissions Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Device /dev/i2c-4 lacks R/W permissions Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Device /dev/i2c-5 lacks R/W permissions Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Device /dev/i2c-6 lacks R/W permissions Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Device /dev/i2c-7 lacks R/W permissions Jun 18 11:05:57 n5z690 org_kde_powerdevil[1537]: [ 1537] Device /dev/i2c-8 lacks R/W permissions Jun 18 11:05:57 n5z690 plasmashell[1492]: kf.plasma.quick: Applet preload policy set to 1 Jun 18 11:05:57 n5z690 plasmashell[1492]: file:///usr/share/plasma/plasmoids/org.kde.desktopcontainment/contents/ui/main.qml:178:25: QML FolderViewDropArea (parent or ancestor of QQuickLayoutAttached): Binding loop > file:///usr/share/plasma/plasmoids/org.kde.desktopcontainment/contents/ui/main.qml:201:9 Jun 18 11:05:57 n5z690 plasmashell[1492]: Toolbox not loading, toolbox package is either invalid or disabled. Jun 18 11:05:58 n5z690 kernel: ixgbe 0000:04:00.0 enp4s0: NIC Link is Up 1 Gbps, Flow Control: None Jun 18 11:05:58 n5z690 NetworkManager[1105]: <info> [1750237558.1752] device (enp4s0): carrier: link connected Jun 18 11:05:58 n5z690 NetworkManager[1105]: <info> [1750237558.1752] device (enp4s0): state change: unavailable -> disconnected (reason 'carrier-changed', managed-type: 'full') Jun 18 11:05:58 n5z690 NetworkManager[1105]: <info> [1750237558.1781] policy: auto-activating connection 'Kabelgebundene Verbindung 1' (7c0c62c6-f22c-3d72-b66f-284047c2444c) Jun 18 11:05:58 n5z690 NetworkManager[1105]: <info> [1750237558.1782] device (enp4s0): Activation: starting connection 'Kabelgebundene Verbindung 1' (7c0c62c6-f22c-3d72-b66f-284047c2444c) Jun 18 11:05:58 n5z690 NetworkManager[1105]: <info> [1750237558.1782] device (enp4s0): state change: disconnected -> prepare (reason 'none', managed-type: 'full') Jun 18 11:05:58 n5z690 NetworkManager[1105]: <info> [1750237558.1783] manager: NetworkManager state is now CONNECTING Jun 18 11:05:58 n5z690 NetworkManager[1105]: <info> [1750237558.1784] device (enp4s0): state change: prepare -> config (reason 'none', managed-type: 'full') Jun 18 11:05:58 n5z690 NetworkManager[1105]: <info> [1750237558.1798] device (enp4s0): state change: config -> ip-config (reason 'none', managed-type: 'full') Jun 18 11:05:58 n5z690 NetworkManager[1105]: <info> [1750237558.1824] dhcp4 (enp4s0): activation: beginning transaction (timeout in 45 seconds) Jun 18 11:05:58 n5z690 avahi-daemon[1107]: Joining mDNS multicast group on interface enp4s0.IPv6 with address fe80::6180:d195:c539:21aa. Jun 18 11:05:58 n5z690 avahi-daemon[1107]: New relevant interface enp4s0.IPv6 for mDNS. Jun 18 11:05:58 n5z690 avahi-daemon[1107]: Registering new address record for fe80::6180:d195:c539:21aa on enp4s0.*. Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Library initialization complete. Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Watching for DPMS state changes unimplemented Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Watching for DPMS state changes unimplemented Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Watching for display connection changes, resolved watch mode = Watch_Mode_Xevent, poll loop interval = 100 millisec Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] extra_stabilization_millisec: 0, stabilization_poll_millisec: 100 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] libddcutil recheck thread 0x555e77405dd0 started Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] libddcutil watch thread 0x555e773dab40 started Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error(s) opening ddc devices Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error EACCES(-13): Keine Berechtigung opening /dev/i2c-0 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error EACCES(-13): Keine Berechtigung opening /dev/i2c-1 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error EACCES(-13): Keine Berechtigung opening /dev/i2c-2 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error(s) opening ddc devices Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error EACCES(-13): Keine Berechtigung opening /dev/i2c-3 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error EACCES(-13): Keine Berechtigung opening /dev/i2c-4 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error EACCES(-13): Keine Berechtigung opening /dev/i2c-5 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error EACCES(-13): Keine Berechtigung opening /dev/i2c-6 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error EACCES(-13): Keine Berechtigung opening /dev/i2c-7 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: Error EACCES(-13): Keine Berechtigung opening /dev/i2c-8 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error EACCES(-13): Keine Berechtigung opening /dev/i2c-0 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error EACCES(-13): Keine Berechtigung opening /dev/i2c-1 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error EACCES(-13): Keine Berechtigung opening /dev/i2c-2 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error EACCES(-13): Keine Berechtigung opening /dev/i2c-3 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error EACCES(-13): Keine Berechtigung opening /dev/i2c-4 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error EACCES(-13): Keine Berechtigung opening /dev/i2c-5 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error EACCES(-13): Keine Berechtigung opening /dev/i2c-6 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error EACCES(-13): Keine Berechtigung opening /dev/i2c-7 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1537] Error EACCES(-13): Keine Berechtigung opening /dev/i2c-8 Jun 18 11:05:58 n5z690 org_kde_powerdevil[1537]: [ 1689] (dw_recheck_displays_func) Recheck interval: Sleeping for 200 milliseconds

STEPS TO REPRODUCE
1.  Load up the Plasma desktop (on CachyOS)
2.  Look up the logs via journalctl 

OBSERVED RESULT
By default, you'll get to see multiple instances of:
1. Device /dev/i2c-* lacks R/W permissions
2. Error EACCES(-13): No permission opening /dev/i2c-* entries [in German as I use DE language]

EXPECTED RESULT
No such warnings/errors.

SOFTWARE/OS VERSIONS
Linux-Kernel: 6.15.3
KDE Plasma Version: 6.3.5
KDE Frameworks Version: 6.15.0
Qt Version: 6.9.1

Monitor: HP X27q, 27", 1440p, 165 Hz

ADDITIONAL INFORMATION
I could solve the problem via debugging with O3 but cannot tell if this is the best or even a real fix:

1. sudo nano /etc/udev/rules.d/99-i2c-permissions.rules
2. Added the following entries and saved it:
# Broader rule: allow seat users + i2c group access to ALL i2c-dev nodes
SUBSYSTEM=="i2c-dev", KERNEL=="i2c-[0-9]*", MODE="0660", GROUP="i2c", TAG+="uaccess"
3. Then enter the following commands:
sudo udevadm control --reload-rules
sudo udevadm trigger -s i2c-dev

I've also reported this issue with CachyOS downstream, as I originally thought it was a downstream issue:
https://discuss.cachyos.org/t/powerdevil-related-errors-when-trying-to-access-i2c-error-eacces-13/10233

However, in a private conversation, distro maintainer Peter Jung told me to bring this issue to your attention.
Comment 1 Marcus Seyfarth 2025-06-20 10:19:58 UTC Comment hidden (spam)
Comment 2 Nate Graham 2025-06-20 15:05:19 UTC Comment hidden (spam)
Comment 3 Nate Graham 2025-06-20 15:06:50 UTC 
Hmm, where is the issue in powerdevil here? Why would it be powerdevil's fault if it doesn't have permission to access a resource provided by a different part of the system?
Comment 4 Marcus Seyfarth 2025-06-20 16:04:17 UTC 
I am probably not the correct person to answer this as I honestly can't tell which project is responsible to solve these errors and owns this problem (therefore filing a downstream CachyOS bug first).

From my limited understanding of the problem it could be a powerdevil problem in needing such a udev rule or a distribution-level problem to require such a rule. All I can tell is that I didn't get these errors in the logs with earlier KDE releases.
Comment 5 Nate Graham 2025-06-20 16:45:15 UTC 
In general this kind of this is controlled by the distro.