I launched the upgrade process to 17.10 when asked for it (on 17.04).
My screen was locked (and off) during the download of the packages but it flashed by waking sometimes (I was in the dark so I noticed that).
Then an hour later, I wanted to see how the upgrade went but I couldn't login anymore. My password was refused (but I could login without problem on a console Ctrl-Alt-F1) so I guess something was wrong with lightDM ?
So I rebooted, and now the boot process fails with
Failed to start Login service which is not related to lightDM anymore but
Edit: systemd-logind log shows that:
Failed to add match for JobRemoved: Connection timed out Failed to fully start daemon: Connectin timed out systemd-logind.service: Main process exited, code=exited, status=1/FAILURE Stopped Login Service. systemd-logind.service: Unit entered failed state. systemd-logind.serivce: Failed with result 'exit-code'.
I can't find much about this on the net