Comment # 11 on bug 1089287 from Fabian Vogt

(In reply to Franck Bui from comment #10)
> (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.

I just checked the source code, it only calls setsid() for the user session, so
after login.

I guess sddm needs to call setsid() before starting X?