Having upgraded from 14.10 to 15.04 my AMD graphics were still working but going to TTY, reset or shutdown would result in a freeze. The logs gave no real clues as to what is going on.
What I found so far: - Selecting the 3.16 kernel in Grub prevents the freeze problem, but also prevents you from using fglrx - Manually selecting the X.org driver (in Software & updates) prevents the freezing too, which makes me think it is purely driver related - Changing /etc/default/grub to "quiet", as mentioned elsewhere for freezing issues on shutdown, does not change anything
What I would really like is to have the fglrx driver again, but I cannot tolerate a freeze everytime X is closing down. I will probably need to downgrade Ubuntu I guess, but if someone has an easier solution then please let me know.