Zombie process or defunction process is a process that has completed execution but still has an entry in the process table. The term zombie process derives from the common definition of zombie—an undead person.

Zombie processes are mostly harmless: they are a process which has finished and is sticking around because their parent hasn’t reaped their exit status. Normally it will do no harm to your system except resource waste.

You can use below command to kill zombie processes:

for i in `ps ax | grep Z | awk {’print $1?}`;do kill -9 $(cat /proc/${i}/status | grep PPid | awk {’print $2?});done