I've pieced this together from other sources, so I thought I'd post it in this forum in case it benefits anyone. So ... I'm one of these people who can't abide Gnome 3, Unity or KDE 4, so cinnamon is heaven-sent. Except that it crashes a lot. Probably three or four times a day, the screen will just freeze, and all I can do is waggle the mouse around. All the applications are still running, but I can't interact with them. For the record, the logs read something like this:
May 9 15:15:10 drongo kernel: [15978.000721] cinnamon: segfault at a5c299 ip b6b343bb sp bfc00510 error 4 in libglib-2.0.so.0.3200.1[b6ad3000+f7000]
At this point, ALT-F2 doesn't work and CTRL-ALT-BACKSPACE doesn't work, but CTRL-ALT-SYSRQ-K does, as long as I'm able to grow an extra finger. But that force-closes all your applications and you lose your work.
So ... this is how to get out of a crash without losing your work! When you crash, stay calm. Don't headbutt the screen or mash the keyboard.
1) Hit CTRL-ALT-F1 to open a shell. Login with your username and password.
2) Run pidof cinnamon and note the process number its running under. You may also like to do ps aux | grep cinnamon if you're curious.
3) Kill cinnamon with this command kill -9 2345, where 2345 was the process number you noted in 2.
4) Start cinnamon again with cinnamon --restart --display=:0 &
5) Hit CTRL-ALT-F7 to return to your desktop. It should start blank and then magically return with all your applications open, and your data intact.
6) Allow yourself a little fistpump.
The bit in step 4) will work assuming the display you're using on your main desktop is display number :0. This is usually the case. However its possible it could be :1 so if it doesn't work initially, you can experiment with that.
Hope this helps someone.