Question

In my Python script, I first launch a subprocess by subprocess.Popen(). Then later on, I want to kill that subprocess by kill -9 Pid.

What I found is that after the kill is executed, the subprocess is “stopped” because the GUI window of that process disappeared immediately. But when I perform a “ps aux” right after the kill, the same process (with same pid) is still shown in the result. The difference is the command of the process is included in a pair of () like below:

root 30506 0.0 0.0 0 0 s000 Z+ 6:13PM
0:00.00 (sample process)

This breaks my process detect logical since the dead process still can be found by ps.

Anyone know why this is happening?

Thanks!

Answer 1

From the manual page of ps:

Z Defunct (“zombie”) process,
terminated but not reaped by its
parent.

That means that the parent didn’t do a waitpid() for the child that died.

Apart from waitpid(), you can avoid that by using a double fork when executing the child.