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SIGPROCMASK(2)              BSD System Calls Manual             SIGPROCMASK(2)

     sigprocmask -- manipulate current signal mask

     #include <&lt;signal.h>&gt;

     sigprocmask(int how, const sigset_t *set, sigset_t *oset);

     The sigprocmask() function examines and/or changes the current signal
     mask (those signals that are blocked from delivery).  Signals are blocked
     if they are members of the current signal mask set.

     If set is not null, the action of sigprocmask() depends on the value of
     the parameter how.  The signal mask is changed as a function of the spec-
     ified set and the current mask.  The function is specified by how using
     one of the following values from <signal.h>:

     SIG_BLOCK    The new mask is the union of the current mask and the speci-
                  fied set.

     SIG_UNBLOCK  The new mask is the intersection of the current mask and the
                  complement of the specified set.

     SIG_SETMASK  The current mask is replaced by the specified set.

     If oset is not null, it is set to the previous value of the signal mask.
     When set is null, the value of how is insignificant and the mask remains
     unset providing a way to examine the signal mask without modification.

     The system quietly disallows SIGKILL or SIGSTOP to be blocked.

     A 0 value indicated that the call succeeded.  A -1 return value indicates
     an error occurred and errno is set to indicated the reason.

     The sigprocmask() call will fail and the signal mask will be unchanged if
     one of the following occurs:

     [EINVAL]           how has a value other than those listed here.

     kill(2), sigaction(2), sigsetops(3), sigsuspend(2)

     The sigprocmask() function call is expected to conform to IEEE Std
     1003.1-1988 (``POSIX.1'').

BSD                              June 4, 1993                              BSD