I believe the problem may be related to this question.
I logged twice to guest account. The first time I've chosen unity and something went wrong. The other time I used gnome shell, it worked for a while, and then I switched to my regular user. I haven't rebooted since. After a few hours I noticed that there are two compiz processes runing using 100% CPU, so I tried to kill them.
Thanks to people on the ubuntu's IRC chat I tried:
sudo killall compiz sudo killall -9 compiz sudo pkill -9 compiz sudo kill -9 15384
None of this commands killed the process (but all of them return 0).
I've also tried restarting X server with
This answer talks about how it may not be possible to kill a process in uninterruptible sleep. I believe that's not the case -- The S column is representing state and the
R symbol means "Running".
This answer tells me that there are some system processes impossible to kill, and their names are in brackets. That's not the case:
bc81 on IRC linked me this answer, and suggested that it may not be possible to kill unity when the Launcher or Unity processes are running. They don't seem to be running though (checked with
sudo ps ax | grep -i launcher).