Sends a signal to each process in the list idlist, if permitted.
signal, if present, is the signal number or the symbolic name of the
signal; see
signal(S)
for details. The leading SIG is optional
when the signal is specified by its symbolic name.
The default for signal is 15, SIGTERM.
If -pgroup is specified, the numbers in idlist are taken
as process group IDs and
the signal is sent to all of the processes in that
process group.
A process group ID of 0 specifies the current process
group.