Linux OS freezes

If it locks up completely, you can REISUB it, which is a safer alternative to just cold rebooting the computer. REISUB by: While holding Alt and the SysReq (Print Screen) keys, type REISUB. R: Switch to XLATE mode E: Send Terminate signal to all processes except for init I: Send Kill signal to all processes except for init S: Sync all mounted file-systems U: Remount file-systems as read-only B: Reboot REISUB is BUSIER backwards, as in "The System is busier than it should be", if you need to remember it. Or mnemonically - R eboot; E ven; I f; S ystem; U tterly; B roken. * In the event you're forced to do this, do it slowly. Let a few seconds pass in between each keypress so that the commands you're invoking have a chance to finish before you go to the next one. http://askubuntu.com/questions/4408/what-should-i-do-when-ubuntu-freezes/36717#36717