system call sends the signal given by
process or a group of processes.
may be one of the signals specified in
or it may be 0, in which case
error checking is performed but no
signal is actually sent.
This can be used to check the validity of
For a process to have permission to send a signal to a process designated
the user must be the super-user, or
the real or saved user ID of the receiving process must match
the real or effective user ID of the sending process.
A single exception is the signal SIGCONT, which may always be sent
to any process with the same session ID as the sender.
In addition, if the
is set to 1, the user is not a super-user, and
the receiver is set-uid, then
only job control and terminal control signals may
be sent (in particular, only SIGKILL, SIGINT, SIGTERM, SIGALRM,
SIGSTOP, SIGTTIN, SIGTTOU, SIGTSTP, SIGHUP, SIGUSR1, SIGUSR2).
| Ifpid, No, is, greater, than, zero:
is sent to the process whose ID is equal to
| Ifpid, No, is, zero:
is sent to all processes whose group ID is equal
to the process group ID of the sender, and for which the
process has permission;
this is a variant of
| Ifpid, No, is, -1:
If the user has super-user privileges,
the signal is sent to all processes excluding
process with ID 1
and the process sending the signal.
If the user is not the super user, the signal is sent to all processes
with the same uid as the user excluding the process sending the signal.
No error is returned if any process could be signaled.
For compatibility with System V,
if the process number is negative but not -1,
the signal is sent to all processes whose process group ID
is equal to the absolute value of the process number.
This is a variant of