I just upgraded to 15.10, and everything went smoothly. One of the first things I did was install
gnome-shell, and switch from
gdm. However, when I restarted, after an initial purple Ubuntu load screen, I got a grey/black screen that never went away. I switched back to
lightdm and everything worked fine again. Is this a problem with
gdm in 15.10, or is there something I am not doing/doing wrong? Thank you!
I have been following this bug report: bugs.launchpad.net/ubuntu/+source/gdm/+bug/1500673 originally linked below by @ulkeshkosh, and there is some new activity there including a suggested fix that worked for one user. I tried this fix, and it didn't work for me, nor did it work for the other commenters, but it might work for someone else visiting this post.
However, a word of warning: one commenter mentions this line in
# Uncomment the line below to force the login screen to use Xorg
#WaylandEnable = false
the commenter does not suggest modifying this line in any way, but being an inexperienced and curious Linux user, I decided to see what happens when I uncommented it, and the results were quite a pain to recover from, so I would suggest that you not experiment in this way.
I finally got
gdmto work properly. Initially I had just installed
gnome-shell, which allowed me to use the GNOME desktop environment, but didn't allow me to use
gdmwith it, as described above, which causes certain other problems, like being unable to lock for example, and other issues mentioned in the comments to the question.
The solution was to install
After that, I changed my display manager back to
and after restarting I was greeted with the appropriate login screen, and everything has worked smoothly so far.
I am assuming this fix worked because of either some extra dependencies that were needed, or some extra tweaks that were made to configuration files when installing that package. I don't have quite enough experience with LInux yet to understand why this worked, but it did, and hopefully it will too for others that have had this problem.
I cannot confirm whether this works or not because I have not tried it, but user @detly suggests in the comments below that
17.04users should use
gdm. Just wanted to highlight this just in case it is useful for users of later versions of Ubuntu.