title: How do detect that cloud-init completed initialization
body: <p>I am configuring an OpenStack box using cloud-init/cloud-config. I intend to wait until it is fully configured before I start using it.</p>
  
  <p>This is not all that hard to do using some marker file or detecting if the cloud-init process is still running, though it seems quite cumbersome to do that in every cloud-init script. Is there some recommended way? Natively supported by cloud-init, ideally?</p>