docs: def ScheduleSystemCronFlows(names=None, token=None):
    """Schedule all the SystemCronFlows found."""
  
    if data_store.RelationalDBEnabled():
      return cronjobs.ScheduleSystemCronJobs(names=names)
  
    errors = []
    for name in config.CONFIG["Cron.disabled_system_jobs"]:
      try:
        cls = registry.AFF4FlowRegistry.FlowClassByName(name)
      except ValueError:
        errors.append("No such flow: %s." % name)
        continue
  
      if not issubclass(cls, SystemCronFlow):
        errors.append("Disabled system cron job name doesn't correspond to "
                      "a flow inherited from SystemCronFlow: %s" % name)
  
    if names is None:
      names = iterkeys(registry.AFF4FlowRegistry.FLOW_REGISTRY)
  
    for name in names:
      cls = registry.AFF4FlowRegistry.FlowClassByName(name)
  
      if not issubclass(cls, SystemCronFlow):
        continue
  
      cron_args = rdf_cronjobs.CreateCronJobFlowArgs(
          periodicity=cls.frequency,
          lifetime=cls.lifetime,
          allow_overruns=cls.allow_overruns)
      cron_args.flow_runner_args.flow_name = name
  
      if cls.enabled:
        enabled = name not in config.CONFIG["Cron.disabled_system_jobs"]
      else:
        enabled = False
  
      job_urn = CronManager.CRON_JOBS_PATH.Add(name)
      with aff4.FACTORY.Create(
          job_urn,
          aff4_type=CronJob,
          mode="rw",
          token=token,
          force_new_version=False) as cron_job:
  
        # If the cronjob was already present we don't want to overwrite the
        # original start_time.
        existing_cron_args = cron_job.Get(cron_job.Schema.CRON_ARGS)
  
        if cron_args != existing_cron_args:
          cron_job.Set(cron_job.Schema.CRON_ARGS(cron_args))
  
        cron_job.Set(cron_job.Schema.DISABLED(not enabled))
  
    if errors:
      raise ValueError("Error(s) while parsing Cron.disabled_system_jobs: %s" %
                       errors)