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 .