After upgrading from kernel 6.17 to 6.18, my system started experiencing very slow boot and shutdown times.
During boot, the process stalls for a long time and the journal shows repeated messages related to v4l2loopback, including errors referencing v4l_id. The same module appears again during shutdown, significantly delaying power-off.
Rolling back to kernel 6.17 immediately restores normal behavior:
Boot time back to normal
Shutdown time back to normal
No v4l2loopback-related warnings or delays
GRUB configuration was verified (update-grub runs cleanly), and the issue is fully reproducible only on 6.18.x. Kernel 6.18.1-1 installs correctly in parallel, but exhibits the same problem when used as the active kernel.
Posting this to document the issue in case it helps others experiencing similar slow boot/shutdown behavior after upgrading to kernel 6.18.x.
There is something to it. I think i noticed too, but it was maybe only a second, so i thought i am imagining. And i do not see any such errors in the logs.
That makes sense. In my case the delay is much more noticeable and consistently reproducible, and it coincides with v4l2loopback messages during both boot and shutdown.
It would also explain why it’s not widely reported yet: depending on hardware and loaded modules, the regression may be subtle or leave no obvious traces in the logs.
I’ll stay on 6.17 for now and keep an eye on newer kernels.
As far as I can tell, the issue is still present in kernel 6.18.x.
At the moment, I think the only reliable workaround is to remain on kernel 6.17, which seems to avoid the slow boot and shutdown behavior and the v4l2loopback-related stalls on my system.
I didn’t need to apply any additional configuration changes.
This should be considered a temporary workaround rather than a fix. I’ll update the thread if the situation changes or if newer kernels behave differently.
That makes sense. On my system, the installed version from the official repos is v4l2loopback 0.15.2, so this would explain the incompatibility I’m seeing with kernel 6.18.x.
Good to know that upstream added compatibility starting with 0.15.3. I’ll keep an eye on the package updates and test again once that version (or newer) is available.
Thanks, Hanzel. You were absolutely right: since v4l2loopback-dkms 0.15.3-1 hit the stable branch, the compatibility with kernel 6.18 is now fixed. I updated, rebuilt the module, and everything works perfectly again — no slow boot, no shutdown delays, no errors.
Thanks for the support and clarification. Issue solved.
Update / Issue Resolved
Just to close this thread with a final update:
The slow boot and shutdown delays with kernel 6.18 were caused by an incompatibility with older versions of v4l2loopback. Since the release of v4l2loopback-dkms 0.15.3-1, which adds proper compatibility with kernel 6.18, the problem is completely gone.
I updated to 0.15.3-1, rebuilt the module, and now:
No slow boot
No shutdown hang
No related journal errors
So the kernel itself was fine; it was the module that needed the update. If anyone is experiencing the same issue, simply make sure you are running v4l2loopback ≥ 0.15.3-1.
Everything now works flawlessly with kernel 6.18. Thread can be considered solved.
