When Linux Hangs

Yes! Linux too hangs. By forcing a manual restart you can put your data at risk.

So when your desktop freezes you can use ATL+CTRL+BackSpace to restart X or GDM.

If that doesn't helps there are other important key sequences that can help you when your computer freezes. They prevent you from file system error during the crash. Also they gives some program to make emergency backup of unsaved work. They are called magic SysRq keys. Please note that they dont work on kernel panic.

To safely restart freezed system,

Press ALT+PrintScreen
While holding them press and release the following keys one by one.
R S E I U B

Please keep in mind that you need to press each key for 2-3 seconds.

These keys are the shortcut for:
Raw Sync tErminate kIll Unmount reBoot

To safely shutdown freezed system,

Press ALT+PrintScreen
While holding them press and release the following keys one by one.
R S E I U O

Please keep in mind that you need to press each key for 2-3 seconds.

These keys are the shortcut for:
Raw Sync tErminate kIll Unmount shutdOwn

There function is:
Raw take control of keyboard back from X
tErminate send SIGTERM to all processes, allowing them to terminate racefully
kIll send SIGKILL to all processes, forcing them to terminate immediately
Sync flush data to disk
Unmount remount all filesystems read-only
reBoot reboot the system
shutdOwn shutdown the system

For more http://en.wikipedia.org/wiki/Magic_SysRq_key