def add_cron(signal, minute, hour, day, month, weekday):
    """Adds cron. The interface to the uWSGI signal cron facility. The syntax is

    .. note:: The last 5 arguments work similarly to a standard crontab,
        but instead of "*", use -1, and instead of "/2", "/3", etc. use -2 and -3, etc.

    :param int signal: Signal to raise.

    :param int minute: Minute 0-59. Defaults to `each`.

    :param int hour: Hour 0-23. Defaults to `each`.

    :param int day: Day of the month number 1-31. Defaults to `each`.

    :param int month: Month number 1-12. Defaults to `each`.

    :param int weekday: Day of a the week number. Defaults to `each`.
        0 - Sunday  1 - Monday  2 - Tuesday  3 - Wednesday
        4 - Thursday  5 - Friday  6 - Saturday

    :rtype: bool

    :raises ValueError: If unable to add cron rule.
    """
