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 undefined 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 sigaction() 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, <signal.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- 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)