I would build in a logic context so that you can be sure. For example, SIGHUP is a non-zero vector when a process is started. It is good practice to null the vector after one's fork/exec (in the child, of course), obviously to avoid the humiliation of having one's nice daemon code quit when the starter-upper terminates. So, then, your test could be "is my SIGHUP vector NULL?" and process accordingly. Use your OS facilities to good purpose, and let them help identify your context, too.