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.Dd December 1, 2019 29.Dt KILL 2 30.Os 31.Sh NAME 32.Nm kill 33.Nd send signal to a process 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In sys/types.h 38.In signal.h 39.Ft int 40.Fn kill "pid_t pid" "int sig" 41.Sh DESCRIPTION 42The 43.Fn kill 44system call sends the signal given by 45.Fa sig 46to 47.Fa pid , 48a 49process or a group of processes. 50The 51.Fa sig 52argument 53may be one of the signals specified in 54.Xr sigaction 2 55or it may be 0, in which case 56error checking is performed but no 57signal is actually sent. 58This can be used to check the validity of 59.Fa pid . 60.Pp 61For a process to have permission to send a signal to a process designated 62by 63.Fa pid , 64the user must be the super-user, or 65the real or saved user ID of the receiving process must match 66the real or effective user ID of the sending process. 67A single exception is the signal SIGCONT, which may always be sent 68to any process with the same session ID as the sender. 69In addition, if the 70.Va security.bsd.conservative_signals 71.Xr sysctl 9 72is set to 1, the user is not a super-user, and 73the receiver is set-uid, then 74only job control and terminal control signals may 75be sent (in particular, only SIGKILL, SIGINT, SIGTERM, SIGALRM, 76SIGSTOP, SIGTTIN, SIGTTOU, SIGTSTP, SIGHUP, SIGUSR1, SIGUSR2). 77.Bl -tag -width Ds 78.It \&If Fa pid No \&is greater than zero : 79The 80.Fa sig 81signal 82is sent to the process whose ID is equal to 83.Fa pid . 84.It \&If Fa pid No \&is zero : 85The 86.Fa sig 87signal 88is sent to all processes whose group ID is equal 89to the process group ID of the sender, and for which the 90process has permission; 91this is a variant of 92.Xr killpg 2 . 93.It \&If Fa pid No \&is -1 : 94If the user has super-user privileges, 95the signal is sent to all processes excluding 96system processes 97(with 98.Dv P_SYSTEM 99flag set), 100process with ID 1 101(usually 102.Xr init 8 ) , 103and the process sending the signal. 104If the user is not the super user, the signal is sent to all processes 105which the caller has permissions to, excluding the process sending the signal. 106No error is returned if any process could be signaled. 107.El 108.Pp 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 or process group can be found corresponding to that specified by 129.Fa pid . 130.It Bq Er EPERM 131The sending process does not have permission to send 132.Va sig 133to any receiving process. 134.El 135.Sh SEE ALSO 136.Xr getpgrp 2 , 137.Xr getpid 2 , 138.Xr killpg 2 , 139.Xr sigaction 2 , 140.Xr sigqueue 2 , 141.Xr raise 3 , 142.Xr init 8 143.Sh STANDARDS 144The 145.Fn kill 146system call is expected to conform to 147.St -p1003.1-90 . 148.Sh HISTORY 149A version of the 150.Fn kill 151function appeared in 152.At v3 . 153The signal number was added to the 154.Fn kill 155function in 156.At v4 . 157