Force reboot a Linux computer
Sometimes when rebooting the computer instead hangs waiting for some process to finish.Luckily you can force it to reboot/shutdown immediately ignoring the shutdown script – but also ignoring syncing hard disks etc.
Enable sysrq and sync disks
echo 1 > /proc/sys/kernel/sysrq
echo s > /proc/sysrq-trigger
Force reboot
echo b > /proc/sysrq-trigger
Force shutdown
echo o > /proc/sysrq-trigger
From here.