SIGSET(3)						     Linux Programmer's Manual							 SIGSET(3)

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       API is obsolete: new applications should use the POSIX signal API (sigaction(2), sigprocmask(2), etc.)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.	(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 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(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  sig-
       nal  (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), feature_test_macros(7), signal(7)

COLOPHON

       This  page is part of release 3.25 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/.

Linux								    2009-03-15								 SIGSET(3)