$ gem install whenever  

$ cd /project  
$ wheneverize .  

every 30.minutes do
  runner "Blog.parseAll"
end

every 30.minutes, :at => 17 do
  runner "PostWeibo.post"
end

every 15.minutes do 
  runner "WeiBo.update"
end

every 30.minutes, :at => 20 do
  runner "RSSGenerator.generate"
end

every 1.day, :at => '2:00 am' do
  command "cd /var/www/mzread/current/public && gunzip -c sitemap1.xml.gz > sitemap1.xml && touch sitemap1.xml "
end

job_type :ruby, "cd :path && /usr/bin/ruby ':task'.rb"  
  
every :hour do  
  ruby 'have_a_rest'  
end  

$ whenever   #不带参数的whenever会显示转换程cron任务的代码，不写入cron任务表  
$ whenever -w #写入cron任务表，开始执行  
$ whenever -c #取消任务 

$ crontab -l  

class MyWorker  
  include Sidekiq::Worker  
  include Sidetiq::Schedulable  
  
  recurrence { daily }  
  
  def perform  
    # do stuff ...  
  end  
end  

require 'clockwork'  
include Clockwork  
  
handler do |job|  
  puts "Running #{job}"  
end  
  
every(10.seconds, 'frequent.job')  
every(3.minutes, 'less.frequent.job')  
every(1.hour, 'hourly.job')  
  
every(1.day, 'midnight.job', :at => '00:00')  

$ clockwork clock.rb  
Starting clock for 4 events: [ frequent.job less.frequent.job hourly.job midnight.job ]  
Triggering frequent.job  

require './config/boot'  
require './config/environment'