sigprocmask - manipulate the signal mask

     #include <signal.h>

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

     Sigprocmask() examines or manipulates the signal mask.  This mask is  the
     set  of  signals that are currently blocked.  The how argument determines
     the action  that  must  be  performed.   In  all  cases  the  signal  set
     referenced  by  oset, if not NULL, will be used to receive the old signal
     mask.  The set argument, if not NULL, will be used to set or  modify  the
     current signal mask.

     How can be one of:

     SIG_BLOCK      Add the signals referenced by set to the mask.

     SIG_UNBLOCK    Remove the signals referenced by set from the mask.

     SIG_SETMASK    Set the signal mask to the set referenced by set.

     The value of how is ignored if set is NULL.

     sigaction(2), sigpending(2), sigsuspend(2), sigset(3).

     Returns 0 on success and -1 on error.  The error code is EFAULT for a bad
     set or oset address, or EINVAL for a bad how argument.

     Kees J. Bot (