1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
|
.\" $OpenBSD: kill.2,v 1.22 2014/12/14 07:42:50 schwarze Exp $
.\" $NetBSD: kill.2,v 1.7 1995/02/27 12:33:53 cgd Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)kill.2 8.3 (Berkeley) 4/19/94
.\"
.Dd $Mdocdate: December 14 2014 $
.Dt KILL 2
.Os
.Sh NAME
.Nm kill
.Nd send signal to a process
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fn kill "pid_t pid" "int sig"
.Sh DESCRIPTION
The
.Fn kill
function sends the signal given by
.Fa sig
to
.Fa pid ,
a
process or a group of processes.
.Fa sig
may be one of the signals specified in
.Xr sigaction 2
or it may be 0, in which case
error checking is performed but no
signal is actually sent.
This can be used to check the validity of
.Fa pid .
.Pp
For a process to have permission to send a signal to a process designated
by
.Fa pid ,
the real or effective user ID of the receiving process must match
that of the sending process or the user must have appropriate privileges
(such as given by a set-user-ID program or the user is the superuser).
A single exception is the signal
.Dv SIGCONT ,
which may always be sent
to any process with the same session ID as the caller.
.Bl -tag -width Ds
.It \&If Fa pid No \&is greater than zero :
.Fa sig
is sent to the process whose ID is equal to
.Fa pid .
.It \&If Fa pid No \&is zero :
.Fa sig
is sent to all processes whose group ID is equal
to the process group ID of the sender, and for which the
process has permission;
this is a variant of
.Xr killpg 3 .
.It \&If Fa pid No \&is -1 :
If the user has superuser privileges,
the signal is sent to all processes excluding
system processes and the process sending the signal.
If the user is not the superuser, the signal is sent to all processes
with the same uid as the user excluding the process sending the signal.
No error is returned if any process could be signaled.
.El
.Pp
Setuid and setgid processes are dealt with slightly differently.
For the non-root user, to prevent attacks against such processes, some signal
deliveries are not permitted and return the error
.Er EPERM .
The following signals are allowed through to this class of processes:
.Dv SIGKILL ,
.Dv SIGINT ,
.Dv SIGTERM ,
.Dv SIGSTOP ,
.Dv SIGTTIN ,
.Dv SIGTTOU ,
.Dv SIGTSTP ,
.Dv SIGHUP ,
.Dv SIGUSR1 ,
.Dv SIGUSR2 .
.Pp
For compatibility with System V,
if the process number is negative but not \-1,
the signal is sent to all processes whose process group ID
is equal to the absolute value of the process number.
This is a variant of
.Xr killpg 3 .
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn kill
will fail and no signal will be sent if:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa sig
is not a valid signal number.
.It Bq Er ESRCH
No process can be found corresponding to that specified by
.Fa pid .
.It Bq Er EPERM
The sending process is not the superuser and its effective
user ID does not match the effective user ID of the receiving process.
When signaling a process group, this error is returned if none of the members
of the group could be signaled.
.El
.Sh SEE ALSO
.Xr getpgrp 2 ,
.Xr getpid 2 ,
.Xr sigaction 2 ,
.Xr killpg 3 ,
.Xr raise 3
.Sh STANDARDS
The
.Fn kill
function is expected to conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn kill
system call first appeared in
.At v3 .
The
.Fa sig
argument was introduced in
.At v4 .
.Sh BUGS
.St -p1003.1-2008
specifies that
.Fn kill 0 sig
should send signal
.Fa sig
to the calling process, but
.Ox
doesn't do so for historical reasons.
|
