code: @Override
    public void start() throws SchedulerException {
  
      if (shuttingDown || closed) {
        throw new SchedulerException(
            "The Scheduler cannot be restarted after shutdown() has been called.");
      }
  
      if (initialStart == null) {
        initialStart = new Date();
        quartzSchedulerResources.getJobStore().schedulerStarted();
        startPlugins();
      }
  
      this.quartzSchedulerThread.togglePause(false);
  
      logger.info("Scheduler started.");
  
      notifySchedulerListenersStarted();
    }
docs: Starts the <code>QuartzScheduler</code>'s threads that fire <code>
  {@link org.quartz.triggers.Trigger}s</code>.
  
  <p>All <code>{@link org.quartz.triggers.Trigger}s</code> that have misfired will be passed to
  the appropriate TriggerListener(s).