Comment # 10 on bug 1089287 from Franck Bui

(In reply to Dr. Werner Fink from comment #3)
> 
> The EE message about
> 
>   [   840.157] (EE) systemd-logind: failed to get session: PID 2837 does not
> belong to any known session
> 
> remains, but this seems to be another problem.  There seems to exist a
> process which already locks the controlling tty on vt7

Hmm it would be interesting to find out the session X server belongs to.

You can try "ps -eo cmd,lsession | grep X" or something similar.

If X server doesn't have a session, it might be SDDM that hasn't properly set
up things before starting the server.