Ubuntu login workaround
Try that Options menu in Ubuntu’s login screen—recently, I happened to use for shutting down without logging-in—and the system will refuse to let you login again. It is apparently a Gnome bug, and I am surprised at the level of its buggyness, considering how polished the rest of Ubuntu is—so far as UI and usability go.
I logged in via Failsafe Terminal and did the following—thanks to those instructions via Ubuntu forums.
cd /homechown username:username username -R /home/usernamecd usernamechmod 755 * -R /home/usernamechmod 644 .dmrcchmod 644 .ICEauthorityexit- Download this example: /inputfiles/fix-ubuntu-login.txt
Stay away from using that Options menu in Ubuntu’s login screen.
Update: Replace username with your actual username in the commands above.