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.\"     @(#)kill.2	8.3 (Berkeley) 4/19/94
.\"
.TH KILL 2 "16 January 1997" GNO "System Calls"
.SH NAME
.BR kill
\- send signal to a process
.SH SYNOPSIS
.br
#include <signal.h>
.sp 1
int
\fBkill\fR (pid_t \fIpid\fR, int \fIsig\fR);
.SH DESCRIPTION
The
.BR kill 
function sends the signal given by
.I sig
to
.IR pid ,
a
process or a group of processes.
Signals are software interrupts; they act just like hardware interrupts
and can also be used for basic IPC (inter-process communication).
.LP
.I Sig
may be one of the signals specified in
.BR signal (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 .
.LP
For a process to have permission to send a signal to a process designated
by
.IR pid ,
the real or effective user ID of the receiving process must match
that of the sending process or the user must have appropriate privileges
(such as given by a set-user-ID program or the user is the super-user).
A single exception is the signal SIGCONT, which may always be sent
to any descendant of the current process.
.LP
If 
.IR pid 
is greater than zero,
.I sig
is sent to the process whose ID is equal to
.I pid.
.LP
If 
.IR pid 
is zero,
.I sig
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
.BR killpg (2).
If 
.IR pid 
is -1, and
if the user has super-user privileges,
the signal is sent to all processes excluding
system processes 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.
.LP
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
.BR killpg (2).
.SH RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and
.IR errno
is set to indicate the error.
.SH ERRORS
.BR Kill 
will fail and no signal will be sent if:
.RS
.IP \fBEINVAL\fR
.I Sig
is not a valid signal number.
.IP \fBESRCH\fR
No process can be found corresponding to that specified by
.RI ( pid )
.IP \fBESRCH\fR
The process id was given as 0
but the sending process does not have a process group.
.IP \fBEPERM\fR
The sending process is not the super-user and its effective
user id does not match the effective user-id of the receiving process.
When signaling a process group, this error is returned if any members
of the group could not be signaled.
.RE
.SH BUGS
Do not attempt to send signals from inside a CDA (Classic Desk Accessory)
or interrupt handler.
.SH SEE ALSO
.BR getpid (2),
.BR getpgrp (2),
.BR killpg (2),
.BR signal (2)
.SH STANDARDS
The
.BR kill 
function is expected to
conform to IEEE Std 1003.1-1988 (POSIX).