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


       Standard C library (libc, -lc)


       #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


       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  This API is obsolete: new applications  should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:

              Reset the disposition of sig to the default.

              Ignore sig.

              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.


       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.


       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).


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue   │
       │sigset(), sighold(), sigrelse(), sigignore()                   │ Thread safety │ MT-Safe │


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


       These functions appeared in glibc 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.


       Before glibc 2.2, sigset() did not unblock sig if disp was specified as a value other than

       Before glibc 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.


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