X11 not working with UBUNTU

As it happens I ended up deleting my /tmp file. after a reboot the machine failed to get to the graphical display (x11). After some research here is what fixed it:

(move to a shell by ctr+alt+F1 or F2 or ... F6)

sudo dpkg-reconfigure xserver-xorg

if that doesn't work you can try something a bit more drastic

sudo apt-get install -- reinstall xserver-xorg

once you get that done try starting the graphic mode:
startx


this made the cursor visible and the wallpaper. But nothing else. The solution was

sudo service gdm restart

This will get you to the password page. You might be surprised that the machine didn't recognize my passport, until you know that /tmp is the place these things are communicated to the system and it has to be writable by everyone:

chmod 777 /tmp

once that is fixed  you should try startx the previous sudo serve command it will work.

Fix X11 Freeze

Sometimes it happens that my UBUNTU Box freezes. Especially after extensive usage of the media. Here are two methods to handle this issue:

1- Going to a different virtual console.

Alt+Ctr+F1 (or F2, .... , F6)

After logging, you can restart the X server using:
$sudo service lightdm restart




P.S: This assumes that your display manager is lightdm (True for ubuntu 12.04). You can check your agent using /etc/X11/default-display-manager


2- If you cannot change to another virtual console, b/c the X server took control of the keyboard. You can try taking the control away from the X server using Sysrq.

Alt+SysRq+r

then try Ctr+Alt+F1.  You can also try Alt+SysRq+k, which kills all programs on the current console.