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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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SIGNAL(3P) POSIX Programmer's Manual SIGNAL(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
signal — signal management
#include <signal.h>
void (*signal(int sig, void (*func)(int)))(int);
The functionality described on this reference page is aligned with
the ISO C standard. Any conflict between the requirements
described here and the ISO C standard is unintentional. This
volume of POSIX.1‐2017 defers to the ISO C standard.
The signal() function chooses one of three ways in which receipt
of the signal number sig is to be subsequently handled. If the
value of func is SIG_DFL, default handling for that signal shall
occur. If the value of func is SIG_IGN, the signal shall be
ignored. Otherwise, the application shall ensure that func points
to a function to be called when that signal occurs. An invocation
of such a function because of a signal, or (recursively) of any
further functions called by that invocation (other than functions
in the standard library), is called a ``signal handler''.
When a signal occurs, and func points to a function, it is
implementation-defined whether the equivalent of a:
signal(sig, SIG_DFL);
is executed or the implementation prevents some implementation-
defined set of signals (at least including sig) from occurring
until the current signal handling has completed. (If the value of
sig is SIGILL, the implementation may alternatively define that no
action is taken.) Next the equivalent of:
(*func)(sig);
is executed. If and when the function returns, if the value of sig
was SIGFPE, SIGILL, or SIGSEGV or any other implementation-defined
value corresponding to a computational exception, the behavior is
undefined. Otherwise, the program shall resume execution at the
point it was interrupted. The ISO C standard places a restriction
on applications relating to the use of raise() from signal
handlers. This restriction does not apply to POSIX applications,
as POSIX.1‐2008 requires raise() to be async-signal-safe (see
Section 2.4.3, Signal Actions).
If the process is multi-threaded, or if the process is single-
threaded and a signal handler is executed other than as the result
of:
* The process calling abort(), raise(), kill(), pthread_kill(),
or sigqueue() to generate a signal that is not blocked
* A pending signal being unblocked and being delivered before
the call that unblocked it returns
the behavior is undefined if the signal handler refers to any
object other than errno with static storage duration other than by
assigning a value to an object declared as volatile sig_atomic_t,
or if the signal handler calls any function defined in this
standard other than one of the functions listed in Section 2.4,
Signal Concepts.
At program start-up, the equivalent of:
signal(sig, SIG_IGN);
is executed for some signals, and the equivalent of:
signal(sig, SIG_DFL);
is executed for all other signals (see exec).
The signal() function shall not change the setting of errno if
successful.
If the request can be honored, signal() shall return the value of
func for the most recent call to signal() for the specified signal
sig. Otherwise, SIG_ERR shall be returned and a positive value
shall be stored in errno.
The signal() function shall fail if:
EINVAL The sig argument is not a valid signal number or an attempt
is made to catch a signal that cannot be caught or ignore a
signal that cannot be ignored.
The signal() function may fail if:
EINVAL An attempt was made to set the action to SIG_DFL for a
signal that cannot be caught or ignored (or both).
The following sections are informative.
None.
The sigaction() function provides a more comprehensive and
reliable mechanism for controlling signals; new applications
should use sigaction() rather than signal().
None.
None.
Section 2.4, Signal Concepts, exec(1p), pause(3p), raise(3p),
sigaction(3p), sigsuspend(3p), waitid(3p)
The Base Definitions volume of POSIX.1‐2017, signal.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 SIGNAL(3P)
Pages that refer to this page: signal.h(0p), stropts.h(0p), nohup(1p), sh(1p), abort(3p), fork(3p), sigaction(3p), sighold(3p), sigsetjmp(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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