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. 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.\" 30.Dd December 1, 2019 31.Dt KILL 2 32.Os 33.Sh NAME 34.Nm kill 35.Nd send signal to a process 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In sys/types.h 40.In signal.h 41.Ft int 42.Fn kill "pid_t pid" "int sig" 43.Sh DESCRIPTION 44The 45.Fn kill 46system call sends the signal given by 47.Fa sig 48to 49.Fa pid , 50a 51process or a group of processes. 52The 53.Fa sig 54argument 55may be one of the signals specified in 56.Xr sigaction 2 57or it may be 0, in which case 58error checking is performed but no 59signal is actually sent. 60This can be used to check the validity of 61.Fa pid . 62.Pp 63For a process to have permission to send a signal to a process designated 64by 65.Fa pid , 66the user must be the super-user, or 67the real or saved user ID of the receiving process must match 68the real or effective user ID of the sending process. 69A single exception is the signal SIGCONT, which may always be sent 70to any process with the same session ID as the sender. 71In addition, if the 72.Va security.bsd.conservative_signals 73.Xr sysctl 9 74is set to 1, the user is not a super-user, and 75the receiver is set-uid, then 76only job control and terminal control signals may 77be sent (in particular, only SIGKILL, SIGINT, SIGTERM, SIGALRM, 78SIGSTOP, SIGTTIN, SIGTTOU, SIGTSTP, SIGHUP, SIGUSR1, SIGUSR2). 79.Bl -tag -width Ds 80.It \&If Fa pid No \&is greater than zero : 81The 82.Fa sig 83signal 84is sent to the process whose ID is equal to 85.Fa pid . 86.It \&If Fa pid No \&is zero : 87The 88.Fa sig 89signal 90is sent to all processes whose group ID is equal 91to the process group ID of the sender, and for which the 92process has permission; 93this is a variant of 94.Xr killpg 2 . 95.It \&If Fa pid No \&is -1 : 96If the user has super-user privileges, 97the signal is sent to all processes excluding 98system processes 99(with 100.Dv P_SYSTEM 101flag set), 102process with ID 1 103(usually 104.Xr init 8 ) , 105and the process sending the signal. 106If the user is not the super user, the signal is sent to all processes 107which the caller has permissions to, excluding the process sending the signal. 108No error is returned if any process could be signaled. 109.El 110.Pp 111If the process number is negative but not -1, 112the signal is sent to all processes whose process group ID 113is equal to the absolute value of the process number. 114This is a variant of 115.Xr killpg 2 . 116.Sh RETURN VALUES 117.Rv -std kill 118.Sh ERRORS 119The 120.Fn kill 121system call 122will fail and no signal will be sent if: 123.Bl -tag -width Er 124.It Bq Er EINVAL 125The 126.Fa sig 127argument 128is not a valid signal number. 129.It Bq Er ESRCH 130No process or process group can be found corresponding to that specified by 131.Fa pid . 132.It Bq Er EPERM 133The sending process does not have permission to send 134.Va sig 135to any receiving process. 136.El 137.Sh SEE ALSO 138.Xr getpgrp 2 , 139.Xr getpid 2 , 140.Xr killpg 2 , 141.Xr sigaction 2 , 142.Xr sigqueue 2 , 143.Xr raise 3 , 144.Xr init 8 145.Sh STANDARDS 146The 147.Fn kill 148system call is expected to conform to 149.St -p1003.1-90 . 150.Sh HISTORY 151A version of the 152.Fn kill 153function appeared in 154.At v3 . 155The signal number was added to the 156.Fn kill 157function in 158.At v4 . 159