Ubuntu screen resolution
This starts the Xorg config process. This doesn't detect and set your video resolution in every circumstance. For example, when you are setting up a virtualized guest this process will rarely set video modes above 800x600 or 1024x768. You usually have to manually edit /etc/X11/xorg.conf. See VirtualBox_notes#Guest video resolution for information on manually setting up video resolution.
sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf_backup sudo dpkg-reconfigure xserver-xorg sudo xinit -- :2
Look for errors:
tail -f /var/log/Xorg.0.log
Restart all servers by bouncing GDM (or KDM or XDM). Sometimes you have to do "stop" then "start" instead of "restart":
sudo /etc/init.d/gdm restart
Or you can start a new X server. Note that this is `xdm` instead of the default Ubuntu `gdm`. This usually comes up on tty8 or tty9 (CTRL-ALT-F8). You can go back to the original X server by pressing CTRL-ALT-F7.
sudo /etc/init.d/xdm start