It provides a way to send commands directly to the kernel through the /proc filesystem.
It is a 'magical' key combo you can hit which the kernel will respond to
regardless of whatever else it is doing, unless it is completely locked up.
It is enabled via a kernel compile time option, CONFIG_MAGIC_SYSRQ, which seems to be standard on most distributions.
So if you're administrating a remote server and suddenly it doesn't respond to commands, like for example :
you need a "magic command".
So, first you must activate the magic SysRq option:
And then you may reboot your system in such way:
Isn't it really cool ?
If you wanna learn more about magic SysRq you can read the sysrq.txt file in the kernel documentation.
of course if you wanna start it during the boot using sysctl you can by typing: