Zombie process is a process observed in Unix/Linux operating system. Zombie process are those process which has finished execution but still have an entry in the process table. This entry for the zombie process is used by the parent to know about the exit status of its child .
After the zombie is removed, its process id and entry in the process table can then be reused but until its entry is in the process table that value cannot be used for other process in case the parent spawns the new process. It will allocate a new pid different from that of zombie process to the new process created.
Zombies can be identified in the output from the ps command in Linux by the presence of a “Z” in the “STAT” column.
To remove zombies from a system, the SIGCHLD signal can be sent to the parent manually, using the kill command. If the parent process still refuses to reap the zombie, the next step would be to remove the parent process. When a process loses its parent, init becomes its new parent. Init periodically executes the wait system call to reap any zombies with init as parent.
