Comment by adrianmonk

Tenth Approach: fork() two processes.

Child 1 exec()s the command.

Child 2 does this:

    signal(SIGALRM, alarm_handler);
    alarm(timeout_length);
    pause();
    exit(0);

Start both children, then call wait(), which blocks until any child exits and returns the pid of the child that exited. If it's the command child, then your command finished. If it's the other child, then the timeout expired.

Now that one child has exited, kill() the other child with SIGTERM and reap it by calling wait() again.

All of this assumes you'll only have these two children going, but if you're writing a small exponential backoff command retry utility, that should be OK.