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signal(2)							    signal(2)


  signal - Modifies signal functions


  #include <&lt;signal.h>&gt;

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


  Interfaces documented	on this	reference page conform to industry standards
  as follows:

  signal():  XPG4, XPG4-UNIX

  Refer	to the standards(5) reference page for more information	about indus-
  try standards	and associated tags.


  sig Defines the signal.  All signals are valid with the exception of SIG-
      KILL and SIGSTOP.

      Specifies	the address of a signal	handler.


  The signal function provides compatibility for older versions	of the
  operating system whose function is a subset of the sigaction function. The
  signal function sets the action associated with a signal. The	function
  parameter uses the values SIG_DFL, SIG_IGN, or it can	point to an address
  of a signal handler.

  A SIG_DFL value specifies the	default	action that is to be taken when	the
  signal is delivered.	A value	of SIG_IGN specifies that the signal has no
  effect on the	receiving process. A pointer to	a function requests that the
  signal be caught; that is, the signal	should cause the function to be
  called. These	actions	are more fully described in the	<&lt;signal.h>&gt; file.


  The sigaction() function provides a more comprehensive and reliable mechan-
  ism for controlling signals and is recommended instead of signal() for new

  [Tru64 UNIX]	The effect of calling the signal function behavior differs
  depending on whether the calling program is linked with either of the
  special libraries, libbsd or libsys5,	which supply BSD or System V signal-
  ing characteristics respectively. If neither library is used,	the behavior
  is the same as that of the sigaction function	with all the flags set to 0
  (zero).  If the libsys5 library is used (through compilation with the	-
  lsys5	switch), then the specified signal is not blocked from delivery	when
  the handler is entered, and the disposition of the signal reverts to
  SIG_DFL when the signal is delivered.	 If the	libbsd library or the
  bsd_signal() function	is used, the behavior is the same as that of the
  sigaction() function with the	SA_RESTART flag	set.

  [Tru64 UNIX]	When compiled in the X/Open UNIX environment, calls to the
  signal() function are	internally renamed by prepending _E to the function
  name.	 When you are debugging	a module that includes the libc	version	of
  the signal() function	and for	which _XOPEN_SOURCE_EXTENDED has been
  defined, use _Esignal	to refer to the	signal() call.	See standards(5) for
  information on when the _XOPEN_SOURCE_EXTENDED macro is defined.


  Upon successful completion of	the signal function, the value of the previ-
  ous signal action is returned. Otherwise, SIG_ERR is returned	and errno is
  set to indicate the error.


  The signal() function	sets errno to the specified values for the following

      The sig parameter	is not a valid signal number or	an attempt was made
      to catch a signal	that cannot be caught or to ignore a signal that can-
      not be ignored.


  Commands:  kill(1)

  Functions:  acct(2), bsd_signal(2), exit(2), kill(2),	pause(3), ptrace(2),
  setjmp(3), sigaction(2), sigblock(2),	sigpause(3), sigprocmask(2), sig-
  stack(2), sigsuspend(2), sigvec(2), umask(2),	wait(2)

  Files:  signal(4)

  Standards:  standards(5)