Grub boot without GUI
When booting, click any key to drop into grub booting menu, click Tab to bring up option line. Append 1 or 3 after the kernel line. Then it will boot without GUI.
This is useful in case the X configuration is messed up. Normal booting will result a locked display as well as locked mouse and keyboard. By booting without GUI, you can get a chance to reinstall graphic drive, or fix X configuration.