Is it possible to disable Unity 3d in Ubuntu 12.10?
I had to use Unity 2d with Ubuntu 12.04 as Unity would constantly crash and restart. This problem persists in 12.10 with any driver I select in the panel, including the open source driver.
Unity (Unity3d is actually a game engine) is the only UI shell in 12.10, which means, you need to install an alternative before removing it (don't think there ever was a way to disable).
To get back to the login screen, try running
You should then be able to select Gnome Classic (no effects) as session from the login scren.
I found another solution that works in my case. Deleting ~/.compiz/session before logging in stops Unity from crashing. This file gets recreated when logging out so you have to delete it before each login.