In my case for apt-get, bash returns command not found, also for sudo. I login as root but the same. The beginning of the problem is update from 12.04 to 12.10 and after login in graphic mode the screen is unreadable with horizontal lines. My system is kernel 3.7.3-101.fc17.x86_64, with C61 GeForce 6150SE nForce430 rev.02. What to do if apt-get is not working?