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SIGNAL(3P)                 POSIX Programmer's Manual                SIGNAL(3P)

PROLOG
       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.
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 appli-
       cation shall ensure that func points to a function to  be  called  when
       that  signal occurs. An invocation of such a function because of a sig-
       nal, or (recursively) of any further functions called by  that  invoca-
       tion  (other than functions in the standard library), is called a "sig-
       nal handler".
       When a signal occurs, and func points to a function, it is  implementa-
       tion-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  cur-
       rent 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 stor-
       age 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. Oth-
       erwise, 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, <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(3P)