Command Section
SIGPROCMASK(2)            FreeBSD System Calls Manual           SIGPROCMASK(2)

     sigprocmask - manipulate current signal mask

     Standard C Library (libc, -lc)

     #include <signal.h>

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

     The sigprocmask() system call 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 how argument.  The signal mask is changed as a function of the
     specified 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
                  specified 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.

     In threaded applications, pthread_sigmask(3) must be used instead of

     The sigprocmask() function returns the value 0 if successful; otherwise
     the value -1 is returned and the global variable errno is set to indicate
     the error.

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

     [EINVAL]           The how argument has a value other than those listed

     kill(2), sigaction(2), sigpending(2), sigsuspend(2), fpsetmask(3),
     pthread_sigmask(3), sigsetops(3)

     The sigprocmask() system call is expected to conform to IEEE Std
     1003.1-1990 (``POSIX.1'').

FreeBSD 11.1-RELEASE-p4           May 7, 2010          FreeBSD 11.1-RELEASE-p4
Command Section