SIGNAL(P)						     POSIX Programmer's Manual							 SIGNAL(P)

NAME

       signal - signal management

SYNOPSIS

       #include <signal.h>

       void (*signal(int sig, void (*func)(int)))(int);

DESCRIPTION

       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
       "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.  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:

	      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).

RETURN VALUE

       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.

ERRORS

       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.

EXAMPLES

       None.

APPLICATION USAGE

       The  sigaction()  function provides a more comprehensive and reliable mechanism for controlling signals; new applications should use sigac-
       tion() rather than signal().

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Signal Concepts , exec() , pause() , sigaction() , sigsuspend() , waitid() , the Base Definitions  volume  of  IEEE Std 1003.1-2001,  <sig-
       nal.h>

COPYRIGHT

       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 .

IEEE
/The Open Group						       2003								 SIGNAL(P)