sigset(3) — Linux manual page


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

NAME         top

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

SYNOPSIS         top

       #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

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

DESCRIPTION         top

       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  This API is obsolete: new applications should use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

       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

       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         top

       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         top

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

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

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

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                             Attribute     Value   │
       │sigset(), sighold(), sigrelse(),      │ Thread safety │ MT-Safe │
       │sigignore()                           │               │         │

CONFORMING TO         top

       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.

NOTES         top

       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         top

       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         top

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

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at

Linux                          2021-03-22                      SIGSET(3)

Pages that refer to this page: sigvec(3)signal(7)signal-safety(7)