1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 4. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)kill.2 8.3 (Berkeley) 4/19/94 29.\" $FreeBSD$ 30.\" 31.Dd April 19, 1994 32.Dt KILL 2 33.Os 34.Sh NAME 35.Nm kill 36.Nd send signal to a process 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In sys/types.h 41.In signal.h 42.Ft int 43.Fn kill "pid_t pid" "int sig" 44.Sh DESCRIPTION 45The 46.Fn kill 47system call sends the signal given by 48.Fa sig 49to 50.Fa pid , 51a 52process or a group of processes. 53The 54.Fa sig 55argument 56may be one of the signals specified in 57.Xr sigaction 2 58or it may be 0, in which case 59error checking is performed but no 60signal is actually sent. 61This can be used to check the validity of 62.Fa pid . 63.Pp 64For a process to have permission to send a signal to a process designated 65by 66.Fa pid , 67the real or effective user ID of the receiving process must match 68that of the sending process or the user must have appropriate privileges 69(such as given by a set-user-ID program or the user is the super-user). 70A single exception is the signal SIGCONT, which may always be sent 71to any process with the same session ID as the caller. 72.Bl -tag -width Ds 73.It \&If Fa pid No \&is greater than zero : 74The 75.Fa sig 76signal 77is sent to the process whose ID is equal to 78.Fa pid . 79.It \&If Fa pid No \&is zero : 80The 81.Fa sig 82signal 83is sent to all processes whose group ID is equal 84to the process group ID of the sender, and for which the 85process has permission; 86this is a variant of 87.Xr killpg 2 . 88.It \&If Fa pid No \&is -1 : 89If the user has super-user privileges, 90the signal is sent to all processes excluding 91system processes 92(with 93.Dv P_SYSTEM 94flag set), 95process with ID 1 96(usually 97.Xr init 8 ) , 98and the process sending the signal. 99If the user is not the super user, the signal is sent to all processes 100with the same uid as the user excluding the process sending the signal. 101No error is returned if any process could be signaled. 102.El 103.Pp 104For compatibility with System V, 105if the process number is negative but not -1, 106the signal is sent to all processes whose process group ID 107is equal to the absolute value of the process number. 108This is a variant of 109.Xr killpg 2 . 110.Sh RETURN VALUES 111.Rv -std kill 112.Sh ERRORS 113The 114.Fn kill 115system call 116will fail and no signal will be sent if: 117.Bl -tag -width Er 118.It Bq Er EINVAL 119The 120.Fa sig 121argument 122is not a valid signal number. 123.It Bq Er ESRCH 124No process can be found corresponding to that specified by 125.Fa pid . 126.It Bq Er ESRCH 127The process id was given as 0 128but the sending process does not have a process group. 129.It Bq Er EPERM 130The sending process is not the super-user and its effective 131user id does not match the effective user-id of the receiving process. 132When signaling a process group, this error is returned if any members 133of the group could not be signaled. 134.El 135.Sh SEE ALSO 136.Xr getpgrp 2 , 137.Xr getpid 2 , 138.Xr killpg 2 , 139.Xr sigaction 2 , 140.Xr raise 3 , 141.Xr init 8 142.Sh STANDARDS 143The 144.Fn kill 145system call is expected to conform to 146.St -p1003.1-90 . 147.Sh HISTORY 148The 149.Fn kill 150function appeared in 151.At v7 . 152