NAME

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

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <signal.h>

       typedef void (*sighandler_t)(int);

       [[deprecated]] sighandler_t sigset(int sig, sighandler_t disp);

       [[deprecated]] int sighold(int sig);
       [[deprecated]] int sigrelse(int sig);
       [[deprecated]] int sigignore(int sig);

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

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

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  This API is obsolete: new applications should use the POSIX  signal  API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

ATTRIBUTES

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

       ┌──────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                                                     │ Attribute     │ Value   │
       ├──────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │sigset(), sighold(), sigrelse(), sigignore()                                  │ Thread safety │ MT-Safe │
       └──────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       POSIX.1-2008.

       sighandler_t
              GNU.  POSIX.1 uses the same type but without a typedef.

HISTORY

       glibc 2.1.  SVr4, POSIX.1-2001.  POSIX.1-2008 marks these functions as obsolete, recommending the use  of
       sigaction(2), sigprocmask(2), pthread_sigmask(3), and sigsuspend(2) instead.

NOTES

       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

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

       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.

SEE ALSO

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