How to Fast Reboot Linux
If you are responsible for Linux servers, there are times when you may need to force an emergency reboot. This is not something you should be doing habitually, but there are times when you have to reboot a server and do not have physical, ILO (Integrated Lights Out), or KVM access. You don't want to be caught in the situation where you've issued a reboot, the server shuts down all services (including sshd!) and then it hangs on a mount point, zombie process, or any number of other issues.
The following commands issued as ROOT will force the Linux kernel to instantly reboot:
echo 1 > /proc/sys/kernel/sysrq echo b > /proc/sysrq-trigger
Bear in mind, system services will not be issued ordinary SIGTERM (kill -15) or even SIGKILL (kill -9) commands. Worse, the filesystem(s) will not be unmounted. The system just disappears. So be sure you have a good reason to do this, and that you are following best practices for backups and server redundancy.