int kill(pid_t pid, int sig);
IEEE Std 1003.1-2017
kill() function shall send a signal to a process or a group of processes specified by pid. The signal to be
sent is specified by sig and is either one from the list given in
<signal.h> or 0. If sig is
null signal), error checking is performed but
no signal is actually sent. The
null signal can be used to check the validity of pid.
For a process to have permission to send a signal to a process designated by pid, unless the sending process has appropriate privileges, the real or effective user ID of the sending process shall match the real or saved set-user-ID of the receiving process.
If pid is greater than
0, sig shall be sent to the process whose process ID is equal to pid.
If pid is
0, sig shall be sent to all processes (excluding an unspecified set of system processes) whose process
group ID is equal to the process group ID of the sender, and for which the process has permission to send a signal.
If pid is
-1, sig shall be sent to all processes (excluding an unspecified set of system processes) for which the
process has permission to send that signal.
If pid is negative, but not
-1, sig shall be sent to all processes (excluding an unspecified set of system
processes) whose process group ID is equal to the absolute value of pid, and for which the process has permission to send a
If the value of pid causes sig to be generated for the sending process, and if sig is not blocked for the
calling thread and if no other thread has sig unblocked or is waiting in a
sigwait() function for sig, either sig or at least one pending unblocked
signal shall be delivered to the sending thread before
The user ID tests described above shall not be applied when sending
SIGCONT to a process that is a member of the same session as
the sending process.
An implementation that provides extended security controls may impose further implementation-defined restrictions on the sending
of signals, including the
null signal. In particular, the system may deny the existence of some or all of the processes specified
kill() function is successful if the process has permission to send sig to any of the processes specified by
kill() fails, no signal shall be sent.
Upon successful completion,
0 shall be returned. Otherwise,
-1 shall be returned and errno set to indicate the error.
kill() function shall fail if:
EINVAL- The value of the sig argument is an invalid or unsupported signal number.
EPERM- The process does not have permission to send the signal to any receiving process.
ESRCH- No process or process group can be found corresponding to that specified by pid.