Comment # 3 on bug 1089287 from Dr. Werner Fink

(In reply to Fabian Vogt from comment #2)
> (In reply to Dr. Werner Fink from comment #0)
> > The current configuration in /usr/lib/sddm/sddm.conf.d/00-general.conf
> > misses the option -keeptty to help the systemd-logind to identify the X
> > server on vt7 with its controlling tty
> 
> Can this have any unexpected side effects or is it safe to enable it in all
> cases?
> 
> I don't think sddm sets the controlling terminal on VT switches, so this
> might actually break it...

This is save (IMHO) ... only startx could run into problems, but startx uses
/etc/X11/xdm/Xservers (where -keeptty is already set)

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