1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)kill.2 8.3 (Berkeley) 04/19/94 7.\" 8.Dd 9.Dt KILL 2 10.Os BSD 4 11.Sh NAME 12.Nm kill 13.Nd send signal to a process 14.Sh SYNOPSIS 15.Fd #include <signal.h> 16.Ft int 17.Fn kill "pid_t pid" "int sig" 18.Sh DESCRIPTION 19The 20.Fn kill 21function sends the signal given by 22.Fa sig 23to 24.Fa pid , 25a 26process or a group of processes. 27.Fa Sig 28may be one of the signals specified in 29.Xr sigaction 2 30or it may be 0, in which case 31error checking is performed but no 32signal is actually sent. 33This can be used to check the validity of 34.Fa pid . 35.Pp 36For a process to have permission to send a signal to a process designated 37by 38.Fa pid , 39the real or effective user ID of the receiving process must match 40that of the sending process or the user must have appropriate privileges 41(such as given by a set-user-ID program or the user is the super-user). 42A single exception is the signal SIGCONT, which may always be sent 43to any descendant of the current process. 44.Bl -tag -width Ds 45.It \&If Fa pid No \&is greater than zero : 46.Fa Sig 47is sent to the process whose ID is equal to 48.Fa pid. 49.It \&If Fa pid No \&is zero : 50.Fa Sig 51is sent to all processes whose group ID is equal 52to the process group ID of the sender, and for which the 53process has permission; 54this is a variant of 55.Xr killpg 2 . 56.It \&If Fa pid No \&is -1 : 57If the user has super-user privileges, 58the signal is sent to all processes excluding 59system processes and the process sending the signal. 60If the user is not the super user, the signal is sent to all processes 61with the same uid as the user excluding the process sending the signal. 62No error is returned if any process could be signaled. 63.El 64.Pp 65For compatibility with System V, 66if the process number is negative but not -1, 67the signal is sent to all processes whose process group ID 68is equal to the absolute value of the process number. 69This is a variant of 70.Xr killpg 2 . 71.Sh RETURN VALUES 72Upon successful completion, a value of 0 is returned. 73Otherwise, a value of -1 is returned and 74.Va errno 75is set to indicate the error. 76.Sh ERRORS 77.Fn Kill 78will fail and no signal will be sent if: 79.Bl -tag -width [EINVAL] 80.It Bq Er EINVAL 81.Fa Sig 82is not a valid signal number. 83.It Bq Er ESRCH 84No process can be found corresponding to that specified by 85.Fa pid . 86.It Bq Er ESRCH 87The process id was given as 0 88but the sending process does not have a process group. 89.It Bq Er EPERM 90The sending process is not the super-user and its effective 91user id does not match the effective user-id of the receiving process. 92When signaling a process group, this error is returned if any members 93of the group could not be signaled. 94.El 95.Sh SEE ALSO 96.Xr getpid 2 , 97.Xr getpgrp 2 , 98.Xr killpg 2 , 99.Xr sigaction 2 100.Sh STANDARDS 101The 102.Fn kill 103function is expected to 104conform to IEEE Std 1003.1-1988 105.Pq Dq Tn POSIX . 106