Now what happens if the forked process is running and we decide that we need to restart the web server? This forked process will be aborted, because when the parent process dies during the restart, it will kill its child processes as well. In order to avoid this, we need to detach the process from its parent session by opening a new session with help of a setsid( ) system call (provided by the POSIX module). This is demonstrated in Example 10-15.

Example 10-15. fork3.pl

use POSIX 'setsid';

defined (my $kid = fork) or die "Cannot fork: $!\n";
if ($kid) {
    # Parent runs this block
}
else {
    # Child runs this block
    setsid or die "Can't start a new session: $!";
    # ...
}

Now the spawned child process has a life of its own, and it doesn't depend on the parent any more.