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1 | .\" Hey Emacs! This file is -*- nroff -*- source. |
2 | .\" | |
3 | .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992 | |
4 | .\" | |
5 | .\" Permission is granted to make and distribute verbatim copies of this | |
6 | .\" manual provided the copyright notice and this permission notice are | |
7 | .\" preserved on all copies. | |
8 | .\" | |
9 | .\" Permission is granted to copy and distribute modified versions of this | |
10 | .\" manual under the conditions for verbatim copying, provided that the | |
11 | .\" entire resulting derived work is distributed under the terms of a | |
12 | .\" permission notice identical to this one. | |
13 | .\" | |
14 | .\" Since the Linux kernel and libraries are constantly changing, this | |
15 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
16 | .\" responsibility for errors or omissions, or for damages resulting from | |
17 | .\" the use of the information contained herein. The author(s) may not | |
18 | .\" have taken the same level of care in the production of this manual, | |
19 | .\" which is licensed free of charge, as they might when working | |
20 | .\" professionally. | |
21 | .\" | |
22 | .\" Formatted or processed versions of this manual, if unaccompanied by | |
23 | .\" the source, must acknowledge the copyright and authors of this work. | |
24 | .\" | |
25 | .\" Modified by Michael Haardt <michael@moria.de> | |
26 | .\" Modified by Thomas Koenig <ig25@rz.uni-karlsruhe.de> | |
27 | .\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu> | |
28 | .\" Modified 1993-07-25 by Rik Faith <faith@cs.unc.edu> | |
29 | .\" Modified 1995-11-01 by Michael Haardt | |
30 | .\" <michael@cantor.informatik.rwth-aachen.de> | |
31 | .\" Modified 1996-04-14 by Andries Brouwer <aeb@cwi.nl> | |
32 | .\" [added some polishing contributed by Mike Battersby <mib@deakin.edu.au>] | |
33 | .\" Modified 1996-07-21 by Andries Brouwer <aeb@cwi.nl> | |
34 | .\" Modified 1997-01-17 by Andries Brouwer <aeb@cwi.nl> | |
35 | .\" Modified 2001-12-18 by Andries Brouwer <aeb@cwi.nl> | |
305a0578 | 36 | .\" Modified 2002-07-24 by Michael Kerrisk <mtk-manpages@gmx.net> |
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37 | .\" Added note on historical rules enforced when an unprivileged process |
38 | .\" sends a signal. | |
305a0578 | 39 | .\" Modified 2004-06-16 by Michael Kerrisk <mtk-manpages@gmx.net> |
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40 | .\" Added note on CAP_KILL |
41 | .\" Modified 2004-06-24 by aeb | |
7f325695 | 42 | .\" Modified, 2004-11-30, after idea from emmanuel.colbus@ensimag.imag.fr |
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43 | .\" |
44 | .TH KILL 2 2004-06-24 "Linux 2.6.7" "Linux Programmer's Manual" | |
45 | .SH NAME | |
46 | kill \- send signal to a process | |
47 | .SH SYNOPSIS | |
48 | .nf | |
49 | .B #include <sys/types.h> | |
50 | .br | |
51 | .B #include <signal.h> | |
52 | .sp | |
53 | .BI "int kill(pid_t " pid ", int " sig ); | |
54 | .fi | |
55 | .SH DESCRIPTION | |
56 | The | |
e511ffb6 | 57 | .BR kill () |
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58 | system call |
59 | can be used to send any signal to any process group or process. | |
60 | .PP | |
61 | If \fIpid\fP is positive, then signal \fIsig\fP is sent to \fIpid\fP. | |
62 | .PP | |
63 | If \fIpid\fP equals 0, then \fIsig\fP is sent to every process in the | |
64 | process group of the current process. | |
65 | .PP | |
30e6794a | 66 | If \fIpid\fP equals \-1, then \fIsig\fP is sent to every process |
cbc84c6e | 67 | for which the calling process has permission to send signals, |
30e6794a | 68 | except for process 1 (init), but see below. |
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69 | .PP |
70 | If \fIpid\fP is less than \-1, then \fIsig\fP is sent to every process | |
71 | in the process group \fI\-pid\fP. | |
72 | .PP | |
73 | If \fIsig\fP is 0, then no signal is sent, but error checking is still | |
74 | performed. | |
75 | ||
76 | For a process to have permission to send a signal | |
77 | it must either be privileged (under Linux: have the | |
78 | .B CAP_KILL | |
79 | capability), or the real or effective | |
80 | user ID of the sending process must equal the real or | |
81 | saved set-user-ID of the target process. | |
82 | In the case of SIGCONT it suffices when the sending and receiving | |
83 | processes belong to the same session. | |
84 | .SH "RETURN VALUE" | |
85 | On success (at least one signal was sent), zero is returned. | |
86 | On error, \-1 is returned, and | |
87 | .I errno | |
88 | is set appropriately. | |
89 | .SH ERRORS | |
90 | .TP | |
91 | .B EINVAL | |
92 | An invalid signal was specified. | |
93 | .TP | |
94 | .B EPERM | |
95 | The process does not have permission to send the signal | |
96 | to any of the target processes. | |
97 | .TP | |
98 | .B ESRCH | |
99 | The pid or process group does not exist. | |
100 | Note that an existing process might be a zombie, | |
101 | a process which already committed termination, but | |
63aa9df0 | 102 | has not yet been \fBwait\fP()ed for. |
fea681da | 103 | .SH NOTES |
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104 | The only signals that can be sent task number one, the |
105 | .I init | |
106 | process, are those for which | |
107 | .I init | |
108 | has explicitly installed signal handlers. | |
109 | This is done to assure the | |
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110 | system is not brought down accidentally. |
111 | .LP | |
2bc2f479 | 112 | POSIX 1003.1-2001 requires that \fIkill(\-1,sig)\fP send \fIsig\fP |
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113 | to all processes that the current process may send signals to, |
114 | except possibly for some implementation-defined system processes. | |
115 | Linux allows a process to signal itself, but on Linux the call | |
8c383102 | 116 | \fIkill(\-1,sig)\fP does not signal the current process. |
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117 | .LP |
118 | POSIX 1003.1-2003 requires that if a process sends a signal to itself, | |
119 | and that process does not have the signal blocked, and no other thread | |
63aa9df0 | 120 | has it unblocked or is waiting for it in \fIsigwait\fP(), at least one |
fea681da | 121 | unblocked signal must be delivered to the sending thread before the |
63aa9df0 | 122 | call of \fIkill\fP() returns. |
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123 | .SH "LINUX HISTORY" |
124 | Across different kernel versions, Linux has enforced different rules | |
125 | for the permissions required for an unprivileged process | |
126 | to send a signal to another process. | |
127 | .\" In the 0.* kernels things chopped and changed quite | |
128 | .\" a bit - MTK, 24 Jul 02 | |
129 | In kernels 1.0 to 1.2.2, a signal could be sent if the | |
130 | effective user ID of the sender matched that of the receiver, | |
131 | or the real user ID of the sender matched that of the receiver. | |
132 | From kernel 1.2.3 until 1.3.77, a signal could be sent if the | |
133 | effective user ID of the sender matched either the real or effective | |
134 | user ID of the receiver. | |
135 | The current rules, which conform to POSIX 1003.1-2001, were adopted | |
136 | in kernel 1.3.78. | |
137 | .SH "CONFORMING TO" | |
b14d4aa5 | 138 | SVr4, SVID, POSIX.1, X/OPEN, 4.3BSD, POSIX 1003.1-2001 |
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139 | .SH "SEE ALSO" |
140 | .BR _exit (2), | |
141 | .BR killpg (2), | |
142 | .BR signal (2), | |
042d7c1b | 143 | .BR sigqueue (2), |
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144 | .BR tkill (2), |
145 | .BR exit (3), | |
146 | .BR capabilities (7), | |
147 | .BR signal (7) |