4.2BSD/usr/man/man2/kill.2

.TH KILL 2 "27 July 1983"
.UC 4
.SH NAME
kill \- send signal to a process
.SH SYNOPSIS
.ft B
kill(pid, sig)
.br
int pid, sig;
.SH DESCRIPTION
.I Kill
sends the signal \fIsig\fP
to a process, specified by the process number
.IR pid .
.I Sig
may be one of the signals specified in
.IR sigvec (2),
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
.IR pid .
.PP
The sending and receiving processes must
have the same effective user ID, otherwise
this call is restricted to the super-user.
A single exception is the signal SIGCONT which may always be sent
to any child or grandchild of the current process.
.PP
If the process number is 0,
the signal is sent to all other processes in the
sender's process group; this is a variant of
.IR killpg (2).
.PP
If the process number is \-1, and the user is the super-user,
the signal is broadcast universally
except to system processes
and the process sending the signal.
.PP
Processes may send signals to themselves.
.SH "RETURN VALUE
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned and
.I errno
is set to indicate the error.
.SH "ERRORS
.I Kill
will fail and no signal will be sent if any of the following
occur:
.TP 15
[EINVAL]
\fISig\fP is not a valid signal number.
.TP 15
[ESRCH]
No process can be found corresponding to that specified by \fIpid\fP.
.TP 15
[EPERM]
The sending process is not the super-user and its effective
user id does not match the effective user-id of the receiving process.
.SH "SEE ALSO"
getpid(2), getpgrp(2), killpg(2), sigvec(2)