Question

I have a perl script which i’d like to spawn a process. It can take a while and most times the parent script will exit. How do I spawn this process so that when the parent is gone it wont turn into a zombie or a defunct process when its done?

edit: I think ive found two methods. Hopefully someone could tell me which one is more appropriate?

1. setting $SIG{CHLD} = ‘IGNORE’;
2. use POSIX ‘setsid’;

edit: The spawned process is also going to be another perl script.

Answer 1

A process becomes as zombie when it exits and before its parent process picks up its status with wait(). When one process forks another and then exits, the child becomes a parent of pid 1 (classically “init”) which immediately reaps the process state. So usually the problem is the reverse of what you describe: The child becomes a zombie (since the parent was not written to deal with SIGCHLD and call wait()) but when the parent exits the zombie is inherited by init and immediately reaped. In fact, the usual solution to decouple a child process fully from its parent (“daemonize”) involves intentionally forking and having the intermediate process exit so that the daemon is immediately a child of init.

Edit: If you’re in shell and want to achieve this effect, try (subprocess &). The parenthesis create a subshell which executes subprocess in the background and then immeidately exits.