The sigfillset function initializes the signal set pointed to
    by set such that you include all signals. A call to sigemptyset
    or sigfillset must be made at least once for each object of type
    sigset_t prior to any other use of that object.

    This function operates on data objects that you can address by
    the application, not on any set of signals known to the system.
    For example, this function does not operate on the set blocked
    from delivery to a process or the set pending for a process.

    See also sigemptyset.