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sigaction(2)			 System	Calls			  sigaction(2)

NAME
       sigaction - detailed signal management

SYNOPSIS
       #include	<signal.h>

       int  sigaction(int  sig,	 const struct sigaction	*act, struct sigaction
       *oact);

DESCRIPTION
       The sigaction() function	allows the calling process to examine or spec-
       ify the action to be taken on delivery of a specific signal. (See  sig-
       nal(3HEAD) for an explanation of	general	signal concepts.)

       The sig argument	specifies the signal and can be	assigned  any  of  the
       signals	specified  in  signal(3HEAD) except  SIGKILL and SIGSTOP. In a
       multithreaded process, sig cannot be SIGWAITING,	SIGCANCEL, or SIGLWP.

       If the argument act is not  NULL, it points to a	structure   specifying
       the new action to be taken when delivering sig. If the argument oact is
       not  NULL, it points to a structure where the action previously associ-
       ated with sig is	to be stored on	return from sigaction().

       The sigaction structure includes	the following members:

       void	 (*sa_handler)();
       void	 (*sa_sigaction)(int, siginfo_t	*, void	*);
       sigset_t	 sa_mask;
       int	 sa_flags;

       The  storage occupied by	sa_handler and sa_sigaction may	overlap, and a
       standard-conforming application (see standards(5)) must	not  use  both
       simultaneously.

       The  sa_handler	member identifies the action to	be associated with the
       specified signal, if the	 SA_SIGINFO flag (see below) is	cleared	in the
       sa_flags	 field of the sigaction	structure. It may take any of the val-
       ues specified in	signal(3HEAD) or that of a user	specified signal  han-
       dler.  If  the	SA_SIGINFO  flag  is  set  in  the sa_flags field, the
       sa_sigaction field specifies a signal-catching function.

       The sa_mask member specifies a set of signals to	be blocked  while  the
       signal  handler	is active. On entry to the signal handler, that	set of
       signals is added	to the set of signals already being blocked  when  the
       signal is delivered. In addition, the signal that caused	the handler to
       be executed will	also be	blocked, unless	the  SA_NODEFER	flag has  been
       specified.  SIGSTOP and	SIGKILL	cannot be blocked (the system silently
       enforces	this restriction).

       The sa_flags member specifies a set of flags used to modify the	deliv-
       ery of the signal. It is	formed by a logical OR of any of the following
       values:

       SA_ONSTACK
	     If	set and	the signal is caught, and if the thread	that is	chosen
	     to	processes a delivered signal has an alternate signal stack de-
	     clared with sigaltstack(2), then it will process  the  signal  on
	     that  stack.  Otherwise,  the signal is delivered on the thread's
	     normal stack.

       SA_RESETHAND
	     If	set and	the signal is caught, the disposition of the signal is
	     reset  to	SIG_DFL	and the	signal will not	be blocked on entry to
	     the signal	handler	(SIGILL, SIGTRAP, and SIGPWR cannot be	 auto-
	     matically reset when delivered; the system	silently enforces this
	     restriction).

       SA_NODEFER
	     If	set and	the signal is caught, the signal will not be automati-
	     cally blocked by the kernel while it is being caught.

       SA_RESTART
	     If	 set  and the signal is	caught,	functions that are interrupted
	     by	the execution  of  this	 signal's  handler  are	 transparently
	     restarted by the system, namely fcntl(2), ioctl(2),  wait(2),
	      waitid(2), and the following functions on	slow devices like ter-
	     minals: getmsg() and getpmsg()  (see  getmsg(2));	 putmsg()  and
	     putpmsg()	(see  putmsg(2));  pread(),  read(),  and readv() (see
	     read(2)); pwrite(), write(), and writev() (see write(2)); recv(),
	     recvfrom(),   and	recvmsg()  (see	 recv(3SOCKET));  and  send(),
	     sendto(), and sendmsg() (see send(3SOCKET). Otherwise, the	 func-
	     tion returns an  EINTR error.

       SA_SIGINFO
	     If	 cleared  and  the signal is caught, sig is passed as the only
	     argument to the signal-catching function. If set and  the	signal
	     is	 caught,   two	additional arguments are passed	to the signal-
	     catching function.	 If the	second argument	is not equal to	 NULL,
	     it	 points	to a siginfo_t structure containing the	reason why the
	     signal was	generated (see	siginfo(3HEAD));  the  third  argument
	     points   to  a  ucontext_t	 structure  containing	the  receiving
	     process's context	when  the  signal  was	delivered  (see	 ucon-
	     text(3HEAD)).

       SA_NOCLDWAIT
	     If	set and	sig equals  SIGCHLD, the system	will not create	zombie
	     processes when children of	the calling process exit. If the call-
	     ing process subsequently issues a wait(2),	it blocks until	all of
	     the calling process's child processes terminate, and then returns
	     -1	with errno set to ECHILD.

       SA_NOCLDSTOP
	     If	 set  and  sig equals SIGCHLD, SIGCHLD will not	be sent	to the
	     calling process when its child processes stop or continue.

       SA_WAITSIG
	     If	set and	sig equals  SIGWAITING,	enables	generation of SIGWAIT-
	     ING signals.  Reserved for	use by the threads library.

RETURN VALUES
       Upon  successful	 completion, 0 is returned. Otherwise, -1 is returned,
       errno is	set to indicate	the error, and no new signal  handler  is  in-
       stalled.

ERRORS
       The sigaction() function	will fail if:

       EINVAL
	     The  value	of the sig argument is not a valid signal number or is
	     equal to  SIGKILL or SIGSTOP. In addition,	if in a	 multithreaded
	     process, it is equal to SIGWAITING, SIGCANCEL, or SIGLWP.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE	TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe		   |
       +-----------------------------+-----------------------------+

SEE ALSO
       kill(1),	 intro(2),  exit(2),  fcntl(2),	 getmsg(2), ioctl(2), kill(2),
       pause(2),   putmsg(2),	read(2),    sigaltstack(2),    sigprocmask(2),
       sigsend(2), sigsuspend(2), wait(2), waitid(2), write(2),	recv(3SOCKET),
       send(3SOCKET),  siginfo(3HEAD),	 signal(3C),   signal(3HEAD),	sigse-
       tops(3C),   thr_create(3THR),   ucontext(3HEAD),	 attributes(5),	 stan-
       dards(5)

NOTES
       The handler routine can be declared:

	      void handler (int	sig, siginfo_t *sip, ucontext_t	*uap);

       The sig argument	is the signal number. The sip argument	is  a  pointer
       (to  space on the stack)	to a siginfo_t structure, which	provides addi-
       tional detail about the delivery	of the signal. The uap argument	 is  a
       pointer	(again	to  space on the stack)	to a ucontext_t	structure (de-
       fined in	<sys/ucontext.h>) which	contains the context from  before  the
       signal.	 It  is	not recommended	that uap be used by the	handler	to re-
       store the context from before the signal	delivery.

SunOS 5.9			  23 Jul 2001			  sigaction(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | ATTRIBUTES | SEE ALSO | NOTES

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