Reboot a linux with zombie process

With unkillable process a simple reboot won't do much.  
Because the system will try to safely kill all process before initiate the reboot, but when you have a zombie process, the hard reboot is the only solution.

To initiate a hard reboot remotely, we have what we call "Magic commands".

Becareful ! This will kill all the running process without save, all non saved data will be lost !

echo 1 > /proc/sys/kernel/sysrq
echo b > /proc/sysrq-trigger

In short, the first line will enable the SysRq access on the kernel and the second line will initiate the "hard-reboot" by the SysRq.

If you want to completely shutdown the server, you can do this.

echo 1 > /proc/sys/kernel/sysrq
echo o > /proc/sysrq-trigger

If you want to keep the SysRq enabled all the time, add this to your sysctl.conf

kernel.sysrq = 1