Thread: How do I stop child processes from becoming defunct?

Hello!

I'm writing a shell and by now it works pretty well, even though I still haven't managed to incorporate ncurses/termios yet. But when I run a program from my shell using "&", and shutdown the program, the child process becomes defunct.

As I understand it I need to handle the child process ending in some way, but how do I handle it without waiting for it? Or do I need two child processes, where the first starts the second and then waits for it, or would that just make the first child process defunct instead of the second?

//Zarniwoop

Are you talking about zombies? If you are, you can waitpid() with WNOHANG to keep from getting zombies, but at the same time you'll not pause your main thread either.

Thank you for all the responses.

itsme86: How do I detect "SIGCHLD" if I don't wait? Or can I check for incoming signals regularly? I assume that would be useful for ignoring Ctrl+C also?

The old-time standard procedure for creating proper daemons is to first fork. Let the parent die. The child will then have init (pid=1) as its parent. Use setsid() to put the child in a process group of its own. Then close all file descriptors (including 0, 1 and 2) and then open 0, 1 and 2 to some harmless device such as /dev/null. Then set up signal handlers (or simply ignore them) and you should be all set.

Most *nix daemons use this method and this is also why you tend to see the pid increased by two each time you start a daemon.

I don't understand how you mean?

What I want to do is the following. I have created a shell, and when the user start e.g. emacs using e.g. "emacs test.c &", he/she can continue using the shell. When the user shuts down emacs, I want to avoid making the process defunct which it becomes now. Actually thanks to running waitpid with WNOHANG every time the user presses enter in the shell I avoid this now, but how would I do what you and itsme86 suggest?

If I create a parent process, which then forks and runs the program, wouldn't that process become defunct in place of the child process?