linux, ubuntu emergency safe reboot

http://en.wikipedia.org/wiki/Magic_SysRq_key#.E2.80.9CREISUB.E2.80.9D_.E2.80.93_safe_reboot
“REISUB” – safe reboot

unRaw (take control of keyboard back from X),
tErminate (send SIGTERM to all processes, allowing them to terminate gracefully),
kIll (send SIGKILL to all processes, forcing them to terminate immediately),
Sync (flush hd write-cache data to disk),
Unmount (remount all filesystems read-only),
reBoot.