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NAME

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

SYNOPSIS

       #define _XOPEN_SOURCE 500
       #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);

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       is   obsolete:  new  applications  should  use  the  POSIX  signal  API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.

       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).

NOTES

       These functions appeared in glibc version 2.1.

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

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

       On  System  V,  the signal() function provides unreliable semantics (as
       when  calling  sigaction()  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(), 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 all versions of glibc up to and including 2.3.5, 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.

CONFORMING TO

       SVr4.  These functions are obsolete: do not use them in new programs.

SEE ALSO

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