zammad/db/migrate/20170515000001_scheduler_status.rb

class SchedulerStatus < ActiveRecord::Migration[4.2]
  def up

    # return if it's a new setup
    return if !Setting.find_by(name: 'system_init_done')

    change_table :schedulers do |t|
      t.string :error_message, null: true
      t.string :status, null: true
    end
  end
end