Udev Rule No Longer Working After Package Upgrade on Arch Linux

[9las]

Hi everyone,

After a recent package upgrade on my Arch Linux system, I noticed that Autorandr stopped automatically switching display configurations when I plugged in or unplugged an external monitor. Despite this issue, running autorandr --detected correctly identified the connected displays, and manually executing autorandr --change worked as expected.

The Issue

To troubleshoot, I ran the following command to monitor udev events:

udevadm monitor --environment --udev

Upon unplugging and re-plugging my external monitor, I observed this output:

monitor will print the received events for:
UDEV - the event which udev sends out after rule processing

UDEV  [6599.927057] online   /devices/system/container/PRP00001:00 (container)
ACTION=online
DEVPATH=/devices/system/container/PRP00001:00
SUBSYSTEM=container
SEQNUM=7788
USEC_INITIALIZED=6599923438

UDEV  [6606.747288] online   /devices/system/container/PRP00001:00 (container)
ACTION=online
DEVPATH=/devices/system/container/PRP00001:00
SUBSYSTEM=container
SEQNUM=7789
USEC_INITIALIZED=6606743526

From this output, I discovered that the udev events for monitor changes were now being registered under the container subsystem with ACTION=online, instead of the expected drm subsystem with ACTION=change.

Solution

To fix this, I updated the udev rule located at:

/usr/lib/udev/rules.d/40-monitor-hotplug.rules

I changed:

- ACTION=="change", SUBSYSTEM=="drm"
+ ACTION=="online", SUBSYSTEM=="container"

After making these changes, I reloaded the udev rules with:

sudo udevadm control --reload-rules
sudo udevadm trigger

This resolved the issue, and Autorandr now automatically switches display configurations as expected.

[tyilo]

I have just updated my Arch Linux system today and my udev rule triggers autorandr fine.