As soon as I finished installing ubuntu 12.04.2, I upgrade it to 12.10 immediately. During reboot, a message showed up said "/tmp is not ready... press s to skip....". The ellipses mean some words I missed because the message disappeared so quickly. Then the screen turns gray(not black) and keeps gray. I press the power button for several senconds to shut it down.
Then I power it on again. The boot procedure stopped after the "ubuntu" logo showed for a second, and then the screen turn gray again.
I noticed something such as
mount -o remount,rw /tmp
mount -o remount,rw /
I don't know where to input them, I just tried what I can. I use the GRUB menu to go into the recovery mode, then boot as normal, because I find it can show me a non-graphic login screen there, like what ctrl+alt+f2 can bring.
So I input the above two commands there. But it dosen't seem to work. ctrl+alt+f7 won't let the graphic desktop show up. Everything keeps the same as before when reboot. Just the gray screen.