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

NAME
     sigprocmask -- manipulate current signal mask

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

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

DESCRIPTION
     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, which can be one of the following values:

     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
     unchanged, providing a way to examine the signal mask without modifica-
     tion.

     The system quietly disallows SIGKILL or SIGSTOP to be blocked.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     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.

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

STANDARDS
     The sigprocmask() function call is expected to conform to IEEE Std
     1003.1-2008 (``POSIX.1'').

BSD                             March 28, 2017                             BSD