1SIGNAL(3P) POSIX Programmer's Manual SIGNAL(3P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 signal — signal management
13
15 #include <signal.h>
16 void (*signal(int sig, void (*func)(int)))(int);
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20 The functionality described on this reference page is aligned with the
21 ISO C standard. Any conflict between the requirements described here
22 and the ISO C standard is unintentional. This volume of POSIX.1‐2017
23 defers to the ISO C standard.
24 The signal() function chooses one of three ways in which receipt of the
26 signal number sig is to be subsequently handled. If the value of func
27 is SIG_DFL, default handling for that signal shall occur. If the value
28 of func is SIG_IGN, the signal shall be ignored. Otherwise, the appli‐
29 cation shall ensure that func points to a function to be called when
30 that signal occurs. An invocation of such a function because of a sig‐
31 nal, or (recursively) of any further functions called by that invoca‐
32 tion (other than functions in the standard library), is called a ``sig‐
33 nal handler''.
34 When a signal occurs, and func points to a function, it is implementa‐
36 tion-defined whether the equivalent of a:
37 signal(sig, SIG_DFL);
40 is executed or the implementation prevents some implementation-defined
42 set of signals (at least including sig) from occurring until the cur‐
43 rent signal handling has completed. (If the value of sig is SIGILL, the
44 implementation may alternatively define that no action is taken.) Next
45 the equivalent of:
46 (*func)(sig);
49 is executed. If and when the function returns, if the value of sig was
51 SIGFPE, SIGILL, or SIGSEGV or any other implementation-defined value
52 corresponding to a computational exception, the behavior is undefined.
53 Otherwise, the program shall resume execution at the point it was
54 interrupted. The ISO C standard places a restriction on applications
55 relating to the use of raise() from signal handlers. This restriction
56 does not apply to POSIX applications, as POSIX.1‐2008 requires raise()
57 to be async-signal-safe (see Section 2.4.3, Signal Actions).
58 If the process is multi-threaded, or if the process is single-threaded
60 and a signal handler is executed other than as the result of:
61 * The process calling abort(), raise(), kill(), pthread_kill(), or
63 sigqueue() to generate a signal that is not blocked
64 * A pending signal being unblocked and being delivered before the
66 call that unblocked it returns
67 the behavior is undefined if the signal handler refers to any object
69 other than errno with static storage duration other than by assigning a
70 value to an object declared as volatile sig_atomic_t, or if the signal
71 handler calls any function defined in this standard other than one of
72 the functions listed in Section 2.4, Signal Concepts.
73 At program start-up, the equivalent of:
75 signal(sig, SIG_IGN);
78 is executed for some signals, and the equivalent of:
80 signal(sig, SIG_DFL);
83 is executed for all other signals (see exec).
85 The signal() function shall not change the setting of errno if success‐
87 ful.
88
90 If the request can be honored, signal() shall return the value of func
91 for the most recent call to signal() for the specified signal sig.
92 Otherwise, SIG_ERR shall be returned and a positive value shall be
93 stored in errno.
94
96 The signal() function shall fail if:
97 EINVAL The sig argument is not a valid signal number or an attempt is
99 made to catch a signal that cannot be caught or ignore a signal
100 that cannot be ignored.
101 The signal() function may fail if:
103 EINVAL An attempt was made to set the action to SIG_DFL for a signal
105 that cannot be caught or ignored (or both).
106 The following sections are informative.
108
110 None.
111
113 The sigaction() function provides a more comprehensive and reliable
114 mechanism for controlling signals; new applications should use sigac‐
115 tion() rather than signal().
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118 None.
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121 None.
122
124 Section 2.4, Signal Concepts, exec, pause(), raise(), sigaction(), sig‐
125 suspend(), waitid()
126 The Base Definitions volume of POSIX.1‐2017, <signal.h>
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130 Portions of this text are reprinted and reproduced in electronic form
131 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
132 table Operating System Interface (POSIX), The Open Group Base Specifi‐
133 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
134 Electrical and Electronics Engineers, Inc and The Open Group. In the
135 event of any discrepancy between this version and the original IEEE and
136 The Open Group Standard, the original IEEE and The Open Group Standard
137 is the referee document. The original Standard can be obtained online
138 at http://www.opengroup.org/unix/online.html .
139 Any typographical or formatting errors that appear in this page are
141 most likely to have been introduced during the conversion of the source
142 files to man page format. To report such errors, see https://www.ker‐
143 nel.org/doc/man-pages/reporting_bugs.html .
144IEEE/The Open Group 2017 SIGNAL(3P)