Killpg sends the signal sig to the process group pgrp. See sigaction(2) for a list of signals. If pgrp is 0, killpg sends the signal to the sending process's process group.
The sending process and members of the process group must have the same effective user ID, or the sender must be the super-user. As a single special case the continue signal SIGCONT may be sent to any process that is a descendant of the current process.
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
SVr4, 4.4BSD (The killpg function call first appeared in 4.0BSD).