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.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)kill.2 8.3 (Berkeley) 4/19/94 33.\" $FreeBSD$ 34.\" 35.Dd April 19, 1994 36.Dt KILL 2 37.Os 38.Sh NAME 39.Nm kill 40.Nd send signal to a process 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In sys/types.h 45.In signal.h 46.Ft int 47.Fn kill "pid_t pid" "int sig" 48.Sh DESCRIPTION 49The 50.Fn kill 51system call sends the signal given by 52.Fa sig 53to 54.Fa pid , 55a 56process or a group of processes. 57The 58.Fa sig 59argument 60may be one of the signals specified in 61.Xr sigaction 2 62or it may be 0, in which case 63error checking is performed but no 64signal is actually sent. 65This can be used to check the validity of 66.Fa pid . 67.Pp 68For a process to have permission to send a signal to a process designated 69by 70.Fa pid , 71the real or effective user ID of the receiving process must match 72that of the sending process or the user must have appropriate privileges 73(such as given by a set-user-ID program or the user is the super-user). 74A single exception is the signal SIGCONT, which may always be sent 75to any process with the same session ID as the caller. 76.Bl -tag -width Ds 77.It \&If Fa pid No \&is greater than zero : 78The 79.Fa sig 80signal 81is sent to the process whose ID is equal to 82.Fa pid . 83.It \&If Fa pid No \&is zero : 84The 85.Fa sig 86signal 87is sent to all processes whose group ID is equal 88to the process group ID of the sender, and for which the 89process has permission; 90this is a variant of 91.Xr killpg 2 . 92.It \&If Fa pid No \&is -1 : 93If the user has super-user privileges, 94the signal is sent to all processes excluding 95system processes 96(with 97.Dv P_SYSTEM 98flag set), 99process with ID 1 100(usually 101.Xr init 8 ) , 102and the process sending the signal. 103If the user is not the super user, the signal is sent to all processes 104with the same uid as the user excluding the process sending the signal. 105No error is returned if any process could be signaled. 106.El 107.Pp 108For compatibility with System V, 109if the process number is negative but not -1, 110the signal is sent to all processes whose process group ID 111is equal to the absolute value of the process number. 112This is a variant of 113.Xr killpg 2 . 114.Sh RETURN VALUES 115.Rv -std kill 116.Sh ERRORS 117The 118.Fn kill 119system call 120will fail and no signal will be sent if: 121.Bl -tag -width Er 122.It Bq Er EINVAL 123The 124.Fa sig 125argument 126is not a valid signal number. 127.It Bq Er ESRCH 128No process can be found corresponding to that specified by 129.Fa pid . 130.It Bq Er ESRCH 131The process id was given as 0 132but the sending process does not have a process group. 133.It Bq Er EPERM 134The sending process is not the super-user and its effective 135user id does not match the effective user-id of the receiving process. 136When signaling a process group, this error is returned if any members 137of the group could not be signaled. 138.El 139.Sh SEE ALSO 140.Xr getpgrp 2 , 141.Xr getpid 2 , 142.Xr killpg 2 , 143.Xr sigaction 2 , 144.Xr raise 3 , 145.Xr init 8 146.Sh STANDARDS 147The 148.Fn kill 149system call is expected to conform to 150.St -p1003.1-90 . 151.Sh HISTORY 152The 153.Fn kill 154function appeared in 155.At v7 . 156