title: Vagrant fail to run triggers: Unknown configuration section 'trigger'
body: <p>Trying to execute a very basic example of triggers usage shown in the official <a href="https://www.vagrantup.com/docs/triggers/usage.html" rel="nofollow noreferrer">docs</a>:</p>
  
  <pre><code>Vagrant.configure("2") do |config|
  
    config.trigger.before :up do |trigger|
      trigger.name = "Hello world"
      trigger.info = "I am running before vagrant up!!"
    end
  
    config.trigger.after :up do |trigger|
      trigger.name = "Hello world"
      trigger.info = "I am running after vagrant up!!"
    end
  
    config.vm.define "ubuntu" do |ubuntu|
      ubuntu.vm.box = "ubuntu/trusty64"
    end
  
  end  
  </code></pre>
  
  <p>Failing with the following error:</p>
  
  <blockquote>
    <p>Vagrant: Unknown configuration section 'trigger'.</p>
  </blockquote>
  
  <p>Any idea?</p>
  
  <hr>
  
  <p>(*) The <a href="https://github.com/emyl/vagrant-triggers" rel="nofollow noreferrer">vagrant-triggers</a> plugin was <a href="https://github.com/hashicorp/vagrant/pull/9713" rel="nofollow noreferrer">merged</a> to  <a href="https://github.com/hashicorp/vagrant/blob/v2.2.5/CHANGELOG.md#210-may-3-2018" rel="nofollow noreferrer">Vagrant 2.1.0</a> in may 2018.</p>