It depends. Do you want to wait for the first to finish before spawning a second? Then you could use system. Do you just want to spawn and forget? Ignore SIGCHLD, and use fork and exec. Do you want at most one child active at all times, which isn't allowed to live for ever? Then you would use fork and exec, and you'd set up handlers for SIGCHLD and SIGALRM.

Abigail