public function crontabCallback(Crontab $crontab, LoopInterface $loop)
    {
        $loop->addTimer(60 - time() % 60, function () use ($crontab) {
            $pid = pcntl_fork();
            if ($pid > 0) {
                return;
            } elseif ($pid == 0) {
                $crontab->start(time());
                exit();
            } else {
                $this->logger->error("could not fork");
                exit();
            }
        });
    }