Question

From a existing question here, someone gave this example code:

int status;
child_pid = fork();
if (child_pid == 0) {
     // in child; do stuff including perhaps exec
} else if (child_pid == -1) {
     // failed to fork 
} else {
     if (waitpid(child_pid, &status, 0) == child_pid) {
          // child exited or interrupted; now you can do something with status
     } else {
          // error etc
     }
 }

Could anyone explain to me what the second parameter of waitpid() is used for?

Answer 1

It is a bit-field for options, the only one available is WNOWAIT, which means to leave the child in a waitable state; a later wait call can be used to again retrieve the child status information.

See: http://linux.die.net/man/2/waitpid