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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 *restrict act, struct
       sigaction *restrict 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.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. 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.h(3HEAD) or that of  a  user  specified  signal
       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  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 alter-
                       nate 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,  SIG-
                       TRAP,  and  SIGPWR  cannot be  automatically reset when
                       delivered; the system silently enforces  this  restric-
                       tion).



       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  fol-
                       lowing   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 sig-
                       nal was generated  (see  siginfo.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  SIGWAIT-
                       ING, SIGCANCEL, or SIGLWP.



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


       tab()     allbox;     cw(2.750000i)|    cw(2.750000i)    lw(2.750000i)|
       lw(2.750000i).  ATTRIBUTE TYPEATTRIBUTE VALUE Interface  StabilityStan-
       dard MT-LevelAsync-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),   waitid(2),   write(2),   recv(3SOCKET),
       send(3SOCKET), siginfo.h(3HEAD),  signal(3C),  signal.h(3HEAD),  sigse-
       tops(3C),  thr_create(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 <&lt;sys/ucontext.h>&gt;) 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 5.10                        1 Nov 2003                      sigaction(2)