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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 December 1, 2017 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 user must be the super-user, or 68the real or saved user ID of the receiving process must match 69the real or effective user ID of the sending process. 70A single exception is the signal SIGCONT, which may always be sent 71to any process with the same session ID as the sender. 72In addition, if the 73.Va security.bsd.conservative_signals 74.Xr sysctl 9 75is set to 1, the user is not a super-user, and 76the receiver is set-uid, then 77only job control and terminal control signals may 78be sent (in particular, only SIGKILL, SIGINT, SIGTERM, SIGALRM, 79SIGSTOP, SIGTTIN, SIGTTOU, SIGTSTP, SIGHUP, SIGUSR1, SIGUSR2). 80.Bl -tag -width Ds 81.It \&If Fa pid No \&is greater than zero : 82The 83.Fa sig 84signal 85is sent to the process whose ID is equal to 86.Fa pid . 87.It \&If Fa pid No \&is zero : 88The 89.Fa sig 90signal 91is sent to all processes whose group ID is equal 92to the process group ID of the sender, and for which the 93process has permission; 94this is a variant of 95.Xr killpg 2 . 96.It \&If Fa pid No \&is -1 : 97If the user has super-user privileges, 98the signal is sent to all processes excluding 99system processes 100(with 101.Dv P_SYSTEM 102flag set), 103process with ID 1 104(usually 105.Xr init 8 ) , 106and the process sending the signal. 107If the user is not the super user, the signal is sent to all processes 108with the same uid as the user excluding the process sending the signal. 109No error is returned if any process could be signaled. 110.El 111.Pp 112For compatibility with System V, 113if the process number is negative but not -1, 114the signal is sent to all processes whose process group ID 115is equal to the absolute value of the process number. 116This is a variant of 117.Xr killpg 2 . 118.Sh RETURN VALUES 119.Rv -std kill 120.Sh ERRORS 121The 122.Fn kill 123system call 124will fail and no signal will be sent if: 125.Bl -tag -width Er 126.It Bq Er EINVAL 127The 128.Fa sig 129argument 130is not a valid signal number. 131.It Bq Er ESRCH 132No process or process group can be found corresponding to that specified by 133.Fa pid . 134.It Bq Er EPERM 135The sending process does not have permission to send 136.Va sig 137to the receiving process. 138.El 139.Sh SEE ALSO 140.Xr getpgrp 2 , 141.Xr getpid 2 , 142.Xr killpg 2 , 143.Xr sigaction 2 , 144.Xr sigqueue 2 , 145.Xr raise 3 , 146.Xr init 8 147.Sh STANDARDS 148The 149.Fn kill 150system call is expected to conform to 151.St -p1003.1-90 . 152.Sh HISTORY 153A version of the 154.Fn kill 155function appeared in 156.At v3 . 157The signal number was added to the 158.Fn kill 159function in 160.At v4 . 161