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 correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
signal - signal management
void (*signal(int sig, void (*func)(int)))(int);
Use of this function is unspecified in a multi-threaded process.
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
When a signal occurs, and func points to a function, it is implementation-defined whether the equivalent of a:
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:
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. If the signal occurs as the result of calling the abort(), raise(), kill(), pthread_kill(), or sigqueue() function, the
signal handler shall not call the raise() function.
If the signal occurs other than as the result of calling abort(), raise(), kill(), pthread_kill(), or sigqueue(), the behavior is unde-
fined if the signal handler refers to any object 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 in the standard library other than one of the functions listed in Signal
Concepts . Furthermore, if such a call fails, the value of errno is unspecified.
At program start-up, the equivalent of:
is executed for some signals, and the equivalent of:
is executed for all other signals (see exec).
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.
The sigaction() function provides a more comprehensive and reliable mechanism for controlling signals; new applications should use sigac-
tion() rather than signal().
Signal Concepts, exec(), pause(), sigaction(), sigsuspend(), waitid(), the Base Definitions volume of IEEE Std 1003.1-2001, <signal.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .
/The Open Group 2003 SIGNAL(3P)