Killpg sends the signal sig to the process group pgrp. See sigvec(2) for a list of signals.
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 sin-
gle special case the continue signal SIGCONT may be sent to any process that is a descendant of the current process.
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and the global variable errno is set to indi-
cate the error.
Killpg will fail and no signal will be sent if any of the following occur:
[EINVAL] Sig is not a valid signal number.
[ESRCH] No process can be found in the process group specified by pgrp.
[ESRCH] The process group was given as 0 but the sending process does not have a process group.
[EPERM] The sending process is not the super-user and one or more of the target processes has an effective user ID different from
that of the sending process.