Stop data loss even on system crash? Remember BUSIER

[Ryan Rix]

Hey,

Ever wonder what the SysRq key does on your computer? Most people have no idea 
that this can be one of the biggest lifesavers in a sticky situation.

When your system hardlocks, either from a nasty process, a bug in X, or for 
some other reason, you risk losing gobs of data if you have to take your 
system offline. Journaling filesystems alleviate this issue to some extent but 
data loss is always a huge risk when taking a system down hard.

But, one simple word can help you take this risk to virtually 0 the next time 
you must take a system down hard (holding the power button for 5 seconds): 
BUSIER - or backwards REISUB, more accurately

R - resets the keyboard driver to raw mode
E - Sends term to all running processes
I - sends kill signal to all processes
S - Syncs all mounted partitions
U - unmount the filesystems and remount as read only
B - reboot

Pressing alt-SysRq and the keys above will send a command to the kernel (by 
passing X, applications and other things which may be causing the hardlock. 
This simple method is failsafe and will work in all situations except 
situations in which the kernel is busy, rather than an application. In that 
situation there is little you can do but hope and pray that the Journal holds.

Ryan.