Forking python, defunct child
fork, python, zombie-process
Solution
To clear the child process in Unix you need to wait on the child, check one of the os.wait(), os.waitpid(), os.wait3() or os.wait4() at http://docs.python.org/2/library/os.html#os.wait
As to why this is so, this is a design decision of Unix. The child process keeps its return value in its process state, if it was to disappear you'll have no return value. The os.wait() also returns to you the return value and then the child process is released and all associated resources are released.
Problem
I have some troubles with Python child processes so I wrote a very simple script: ``` import os import sys import time pid = os.fork() if pid: #parent time.sleep(30) else: #child #os._exit(0) sys.exit() ``` While parent process is sleeping I launch ``` ps fax | grep py[t]hon ``` And I read this output ``` 2577 ? S 0:00 python /home/pi/python/GPIO/GPIODaemon.py restart 2583 ? Z 0:00 \_ [python] <defunct> ``` Using `sys.exit()`or`os._exit(0)` there is always a Zombie process and I'm unable to understand why. Working on my more complex code I was thinking that there was some resources that child processes were keeping locked, but on this simplified code child has no file/socket/db connection at all! Why is child process zombiefied?