Wait for and/or kill process grandchildren produced by fork

Question

I fork() into process X and Y, afterwards Y forks() again into itself and process Z multiple times.

Now process Y is some kind of \"listene

Answer 1

Your question does a terrific job of making the actual problem hard to understand. Still, I believe I can discern the following: "I want to get rid of the zombies". Well, don't we all.

There are multiple ways of doing this:

• Have Y ignore SIGCHLD. forked children will not turn into zombies when they die
• Have Y periodically reap (wait) for any children

It's your choice which one you use, but it seems to me the first is what you want.

Answer 2

The only process that can acquire exit statuses from its distant Nth generation grand-children is the 'init' process, and that is a special case rule implemented by the kernel.

In general, a process can only wait for its direct children to die; it cannot wait for its children's progeny to die.

Morbid business...

---

If you're in charge of the process Y code, or can influence it, perhaps that process should set signal(SIGCHLD, SIG_IGN) so that the Z processes do not create zombies. Process X could even do that itself while it forks the Y processes by ignoring SIGCHILD in the child process after the fork() and before any exec*() of the Y process. This only gets overridden if the Y processes explicitly set a different handler for SIGCHLD. And if the Y code explicitly sets SIGCHLD handling and does not actually collect its zombies (Z processes), then you can report a bug in the Y code.

Answer 3

This is not supported. If your sole intent is to prevent the 'Z' processes (i.e., the grandchildren) from turning into zombies, you can use setsid(). If you actually need their exit status, however, you really need to reap them from the 'Y' processes.