Comment 9 for bug 196464

I have this issue again and again ... Yesterday I started dist-upgrade and lock the screen to have some coffee. When I returned I had the same issue I couldn't get the unlock password dialog, switching to text terminal I was able to correct the ownership of that /tmp/.gdm* file. After this move I was able to get the unlock dialog and everything works. Please note that there is 'full filesystem' or 'unwritable home' issue here, I checked these, since you had the message that this could cause my problem.