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

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

       #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       is  obsolete:  new applications should use the POSIX signal API (sigac-
       tion(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  re-
       moved 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

       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 suc-
       cess; on error, these functions return -1 and set errno to indicate the

       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 at-

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

       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_NODE-
       FER).  On BSD,  signal()  provides  reliable  semantics.   POSIX.1-2001
       leaves  these  aspects of signal() unspecified.  See signal(2) for fur-
       ther details.

       In order to wait for a signal, BSD and System V both provided  a  func-
       tion  named  sigpause(3), but this function has a different argument on
       the two systems.  See sigpause(3) for details.

       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 previ-
       ous 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)

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       description  of  the project, information about reporting bugs, and the
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Linux                             2017-09-15                         SIGSET(3)
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