Forcing a reboot when reboot and shutdown don't work
Sometimes issuing the reboot and shutdown commands fail to reboot a system.
This may be the case if the filesystem has gone read-only. The commands below
can be used tell the kernel to reboot the system. You need to be root or sudo
to use the commands.
echo 1 > /proc/sys/kernel/sysrq
echo b > /proc/sysrq-trigger
for a full explanation.