mimikael

The "magic SysRq key" provides a way to send commands directly to the
kernel through the /proc filesystem. It is enabled via a kernel compile
time option, CONFIG_MAGIC_SYSRQ, which seems to be standard on most
distributions. First you must activate the magic SysRq option:

echo 1 > /proc/sys/kernel/sysrq
When you are ready to reboot the machine simply run the following:

echo b > /proc/sysrq-trigger
This does not attempt to unmount or sync filesystems, so it should only
be used when absolutely necessary, but if your drive is already failing
then that may not be a concern.