NAME

       sigset, sighold, sigrelse, sigignore - System V signal API

SYNOPSIS

       #include <signal.h>

       typedef void (*sighandler_t)(int);

       sighandler_t sigset(int sig, sighandler_t disp);

       int sighold(int sig);

       int sigrelse(int sig);

       int sigignore(int sig);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sigset(), sighold(), sigrelse(), sigignore():
           _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION

       These  functions  are  provided  in  glibc as a compatibility interface for programs that make use of the
       historical System V signal API.  This API is obsolete: new applications should use the POSIX  signal  API
       (sigaction(2), sigprocmask(2), etc.)

       The  sigset()  function modifies the disposition of the signal sig.  The disp argument can be the address
       of a signal handler function, or one of the following constants:

       SIG_DFL
              Reset the disposition of sig to the default.

       SIG_IGN
              Ignore sig.

       SIG_HOLD
              Add sig to the process's signal mask, but leave the disposition of sig unchanged.

       If disp specifies the address of a signal handler, then sig is added to the process's signal mask  during
       execution of the handler.

       If disp was specified as a value other than SIG_HOLD, then sig is removed from the process's signal mask.

       The dispositions for SIGKILL and SIGSTOP cannot be changed.

       The sighold() function adds sig to the calling process's signal mask.

       The sigrelse() function removes sig from the calling process's signal mask.

       The sigignore() function sets the disposition of sig to SIG_IGN.

RETURN VALUE

       On  success,  sigset()  returns  SIG_HOLD  if  sig  was blocked before the call, or the signal's previous
       disposition if it was not blocked before the call.  On error, sigset() returns  -1,  with  errno  set  to
       indicate the error.  (But see BUGS below.)

       The  sighold(),  sigrelse(),  and  sigignore()  functions  return 0 on success; on error, these functions
       return -1 and set errno to indicate the error.

ERRORS

       For sigset() see the ERRORS under sigaction(2) and sigprocmask(2).

       For sighold() and sigrelse() see the ERRORS under sigprocmask(2).

       For sigignore(), see the errors under sigaction(2).

CONFORMING TO

       SVr4, POSIX.1-2001.  These functions are obsolete: do not use them in new programs.   POSIX.1-2008  marks
       sighold(),  sigignore(),  sigpause(),  sigrelse(),  and  sigset()  as  obsolete,  recommending the use of
       sigaction(2), sigprocmask(2), pthread_sigmask(3), and sigsuspend(2) instead.

NOTES

       These functions appeared in glibc version 2.1.

       The sighandler_t type is a GNU extension; it is used on this page only to  make  the  sigset()  prototype
       more easily readable.

       The  sigset()  function  provides  reliable  signal handling semantics (as when calling sigaction(2) with
       sa_mask equal to 0).

       On System V, the signal() function provides unreliable  semantics  (as  when  calling  sigaction(2)  with
       sa_mask equal to SA_RESETHAND | SA_NODEFER).  On BSD, signal() provides reliable semantics.  POSIX.1-2001
       leaves these aspects of signal() unspecified.  See signal(2) for further details.

       In order to wait for a signal, BSD and System V both provided a  function  named  sigpause(3),  but  this
       function has a different argument on the two systems.  See sigpause(3) for details.

BUGS

       In versions of glibc before 2.2, sigset() did not unblock sig if disp was specified as a value other than
       SIG_HOLD.

       In versions of glibc before 2.5, sigset() does not correctly  return  the  previous  disposition  of  the
       signal  in two cases.  First, if disp is specified as SIG_HOLD, then a successful sigset() always returns
       SIG_HOLD.  Instead, it should return the previous disposition  of  the  signal  (unless  the  signal  was
       blocked,  in  which  case SIG_HOLD should be returned).  Second, if the signal is currently blocked, then
       the return value of a successful sigset() should be SIG_HOLD.  Instead, the previous disposition  of  the
       signal is returned.  These problems have been fixed since glibc 2.5.

SEE ALSO

       kill(2), pause(2), sigaction(2), signal(2), sigprocmask(2), raise(3), sigpause(3), sigvec(3), signal(7)

COLOPHON

       This  page  is  part  of  release 3.54 of the Linux man-pages project.  A description of the project, and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.