1 .\" Copyright (c) 1980, 1991, 1993
2 .\" The Regents of the University of California. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
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.
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
28 .\" @(#)signal.3 8.3 (Berkeley) 4/19/94
29 .\" $FreeBSD: src/lib/libc/gen/signal.3,v 1.17.2.9 2003/03/13 18:05:37 trhodes Exp $
36 .Nd simplified software signal facilities
41 .\" The following is Quite Ugly, but syntactically correct. Don't try to
44 .Fn (*signal "int sig" "void (*func)(int)))(int"
48 equivalent but easier to read typedef'd version:
49 .Ft typedef "void (*sig_t) (int)" ;
51 .Fn signal "int sig" "sig_t func"
56 is a simplified interface to the more general
60 Signals allow the manipulation of a process from outside its
61 domain as well as allowing the process to manipulate itself or
62 copies of itself (children).
63 There are two general types of signals:
64 those that cause termination of a process and those that do not.
65 Signals which cause termination of a program might result from
66 an irrecoverable error or might be the result of a user at a terminal
67 typing the `interrupt' character.
68 Signals are used when a process is stopped because it wishes to access
69 its control terminal while in the background (see
71 Signals are optionally generated
72 when a process resumes after being stopped,
73 when the status of child processes changes,
74 or when input is ready at the control terminal.
75 Most signals result in the termination of the process receiving them
77 is taken; some signals instead cause the process receiving them
78 to be stopped, or are simply discarded if the process has not
86 function allows for a signal to be caught, to be ignored, or to generate
88 These signals are defined in the file
90 .Bl -column SIGCKPTEXITXX "create core imagexxx"
91 .It Sy NAME Ta Sy Default Action Ta Sy Description
92 .It Dv SIGHUP Ta terminate process Ta terminal line hangup
93 .It Dv SIGINT Ta terminate process Ta interrupt program
94 .It Dv SIGQUIT Ta create core image Ta quit program
95 .It Dv SIGILL Ta create core image Ta illegal instruction
96 .It Dv SIGTRAP Ta create core image Ta trace trap
97 .It Dv SIGABRT Ta create core image Ta abort program (formerly Dv SIGIOT )
98 .It Dv SIGEMT Ta create core image Ta emulate instruction executed
99 .It Dv SIGFPE Ta create core image Ta floating-point exception
100 .It Dv SIGKILL Ta terminate process Ta kill program
101 .It Dv SIGBUS Ta create core image Ta bus error
102 .It Dv SIGSEGV Ta create core image Ta segmentation violation
103 .It Dv SIGSYS Ta create core image Ta non-existent system call invoked
104 .It Dv SIGPIPE Ta terminate process Ta write on a pipe with no reader
105 .It Dv SIGALRM Ta terminate process Ta real-time timer expired
106 .It Dv SIGTERM Ta terminate process Ta software termination signal
107 .It Dv SIGURG Ta discard signal Ta urgent condition present on socket
108 .It Dv SIGSTOP Ta stop process Ta stop (cannot be caught or ignored)
109 .It Dv SIGTSTP Ta stop process Ta stop signal generated from keyboard
110 .It Dv SIGCONT Ta discard signal Ta continue after stop
111 .It Dv SIGCHLD Ta discard signal Ta child status has changed
112 .It Dv SIGTTIN Ta stop process Ta background read attempted from control terminal
113 .It Dv SIGTTOU Ta stop process Ta background write attempted to control terminal
114 .It Dv SIGIO Ta discard signal Ta I/O is possible on a descriptor (see Xr fcntl 2 )
115 .It Dv SIGXCPU Ta terminate process Ta cpu time limit exceeded (see Xr setrlimit 2 )
116 .It Dv SIGXFSZ Ta terminate process Ta file size limit exceeded (see Xr setrlimit 2 )
117 .It Dv SIGVTALRM Ta terminate process Ta virtual time alarm (see Xr setitimer 2 )
118 .It Dv SIGPROF Ta terminate process Ta profiling timer alarm (see Xr setitimer 2 )
119 .It Dv SIGWINCH Ta discard signal Ta window size change
120 .It Dv SIGINFO Ta discard signal Ta status request from keyboard
121 .It Dv SIGUSR1 Ta terminate process Ta user defined signal 1
122 .It Dv SIGUSR2 Ta terminate process Ta user defined signal 2
123 .It Dv SIGCKPT Ta checkpoint process Ta checkpoint
124 .It Dv SIGCKPTEXIT Ta terminate process Ta checkpoint and exit
129 argument specifies which signal was received.
132 procedure allows a user to choose the action upon receipt of a signal.
133 To set the default action of the signal to occur as listed above,
139 resets the default action.
144 This will cause subsequent instances of the signal to be ignored
145 and pending instances to be discarded.
149 further occurrences of the signal are
150 automatically blocked and
154 The handled signal is unblocked when the
156 the process continues from where it left off when the signal occurred.
158 Unlike previous signal facilities, the handler
159 func() remains installed after a signal has been delivered.
162 For some system calls, if a signal is caught while the call is
163 executing and the call is prematurely terminated,
164 the call is automatically restarted.
165 (The handler is installed using the
169 The affected system calls include
177 on a communications channel or a low speed device
182 However, calls that have already committed are not restarted,
183 but instead return a partial success (for example, a short read count).
184 These semantics could be changed with
187 When a process which has installed signal handlers forks,
188 the child process inherits the signals.
189 All caught signals may be reset to their default action by a call
193 ignored signals remain ignored.
197 for a list of functions
198 that are considered safe for use in signal handlers.
200 The previous action is returned on a successful call.
203 is returned and the global variable
205 is set to indicate the error.
210 will fail and no action will take place if one of the
217 is not a valid signal number.
219 An attempt is made to ignore or supply a handler for