sudo /etc/init.d/gdm restart - restart X (GNOME)

sudo /etc/init.d/kdm restart - restart X (KDE)

(file) /etc/Xll/xorg.conf - display configuration

sudo dpkg-reconfigure -phigh xserver-xorg - reset X configuration

Ctrl+Alt+Bksp - restart X display if frozen

Ctrl+Alt+FN - switch to tty N

Ctrl+Alt+F7 - switch back to X display