In terms of call-return behaviour, how are the fork() and exec() system calls different from other system calls?

Question

Fork returns twice-

• once in parent

• once in child

But, how is exec() different from other system calls in terms of call and return behaviour?

Answer 1

Actually, there are a few which don't obey the "returns once" paradigm.

A call to fork() returns once or twice - the latter on success where it returns once in the parent and once in the child, the former on failure where it simply returns once in the parent.

A call to exec() will return on failure but, if successful, the current process is simply overwritten with a new program.

There are others, such as exit() or abort(), which are not expected to return at all.