sigaction(2)							   System Calls 						      sigaction(2)

NAME

       sigaction - detailed signal management

SYNOPSIS

       #include <signal.h>

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

DESCRIPTION

       The sigaction() function allows the calling process to examine or specify the action to be taken on delivery of a specific signal. See sig-
       nal.h(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.h(3HEAD) except  SIGKILL and SIGSTOP.

       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 associated 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 values specified in signal.h(3HEAD) or that of a user specified sig-
       nal handler. 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 delivery of the signal. It is formed by a logical OR of any of the follow-
       ing 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  declared	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  automatically reset when delivered; the system silently
		       enforces this restriction).

       SA_NODEFER      If set and the signal is caught, the signal will not be automatically 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(3C), waitid(2), and the following functions on slow devices like
		       terminals: 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 function 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  sig-
		       info.h(3HEAD));	the  third  argument  points to a ucontext_t structure containing the receiving process's context when the
		       signal was delivered (see ucontext.h(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 calling process subsequently issues a wait(3C), 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.

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
       installed.

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	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed 		   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+
       |Standard		     |See standards(5). 	   |
       +-----------------------------+-----------------------------+

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), waitid(2), write(2), recv(3SOCKET), send(3SOCKET), siginfo.h(3HEAD), signal(3C), signal.h(3HEAD), sigsetops(3C),
       ucontext.h(3HEAD), wait(3C), attributes(5), standards(5)

NOTES

       The handler routine can be declared:

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

       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 ucp argument is a pointer (again to space on the stack) to a ucontext_t structure
       (defined in <sys/ucontext.h>) which contains the context from before the signal.  It is not recommended that ucp be used by the handler	to
       restore the context from before the signal delivery.

SunOS 5.11							    23 Mar 2005 						      sigaction(2)