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
See 
www.linuxjournal.com/content/rebooting-magic-way
for a full explanation.
01/03/2015