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#1 2024-12-04 15:11:21

flooklab
Member
Registered: 2024-12-03
Posts: 2

Infrequent random login freeze after waking up from suspend

Hey all,

every once in a while (not often, maybe twice a year) it happens that I cannot unlock/login after waking my system up from suspend.
I can normally type my session unlock password to the LightDM greeter but after pressing "unlock" nothing will happen
(the greeter seems to freeze for a while). I can still switch to another TTY and type username/password but cannot
actually login there either (also freezes for a while). After a reboot everything is back to normal.

The problem is that there is nothing helpful in the journal. If I compare to a successful suspend/wakeup cycle the only real
difference is that the following lines are missing in journalctl (which is no surprise as it fails to switch back to the running session):

systemd[1]: Stopping Session cX of User lightdm...
lightdm[...]: pam_unix(lightdm-greeter:session): session closed for user lightdm
systemd[1]: session-cX.scope: Deactivated successfully.
systemd[1]: Stopped Session cX of User lightdm.
systemd-logind[...]: Removed session cX.

Because the overall system does not really freeze and login via TTY is also affected I suppose that this problem is perhaps somehow related to PAM, though.
Does anyone know what could go wrong here? As I said, this problem rarely happens and thus I cannot really reproduce or debug it.

Concerning the logs: is there any way for me to provide some useful logs the next time this might happen (without having to have debug level logs for half a year...)?
Also, this time I rebooted using SysRq without trying anything else first; would it make any difference for the journal completeness if I tried e.g. a Ctrl+Alt+Del from tty1 or so?

System configuration:

  • Display server: Xorg

  • Display manager: LightDM

  • Desktop environment: Xfce

  • Screen locker: light-locker

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#2 2025-04-07 15:53:04

flooklab
Member
Registered: 2024-12-03
Posts: 2

Re: Infrequent random login freeze after waking up from suspend

This happened again yesterday and I managed to restart the system via Ctrl+Alt+Del, but unfortunately I cannot provide much more information.

One unusual thing I noticed, though, is that there was a frozen mouse cursor on a black background for maybe a second right after I had triggered the wake-up and right before the lock screen showed up. Then (as always) I could normally type my password but could not unlock the sesson, nor login on another TTY.

(I failed to save the Xorg logs by the way, maybe there was something interesting in them...)

I checked/compared the journals again and here is the part that is *missing* this time (i.e. what was not reached due to the login freeze):

systemd[1]: Created slice User Slice of UID 973.
systemd[1]: Starting User Runtime Directory /run/user/973...
systemd[1]: Finished User Runtime Directory /run/user/973.
systemd[1]: Starting User Manager for UID 973...
(systemd)[2315]: pam_warn(systemd-user:setcred): function=[pam_sm_setcred] flags=0x8002 service=[systemd-user] terminal=[<unknown>] user=[lightdm] ruser=[<unknown>] rhost=[<unknown>]
(systemd)[2315]: pam_unix(systemd-user:session): session opened for user lightdm(uid=973) by lightdm(uid=0)
systemd-logind[856]: New session 4 of user lightdm.
systemd[2315]: Queued start job for default target Main User Target.
systemd[2315]: Created slice User Application Slice.
systemd[2315]: Reached target Paths.
systemd[2315]: Reached target Timers.
systemd[2315]: Starting D-Bus User Message Bus Socket...
systemd[2315]: Listening on ...
...
systemd[2315]: Reached target Sockets.
systemd[2315]: Reached target Basic System.
systemd[2315]: Reached target Main User Target.
systemd[2315]: Startup finished in 200ms.
systemd[1]: Started User Manager for UID 973.
systemd[2315]: Created slice User Core Session Slice.
...

So obviously the LightDM user usually opens some session, which it didn't do this time. Don't know what you can deduce from this, maybe a question to LightDM people?
A LightDM issue wouldn't explain the login freeze on TTY, though, would it?

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