title: Unable to find image error, How to setup proxy to download images
body: <p>I need setup the corporation proxy in order Docker can download the images from public registry.</p>
  
  <pre><code>$ sudo docker run hello-world 
  Unable to find image 'hello-world:latest' locally 
  Pulling repository docker.io/library/hello-world 
  Error while pulling image: Get https://index.docker.io/v1/repositories/library/hello-world/images: dial tcp: lookup index.docker.io: no such host
  </code></pre>
  
  <p>I'm using Ubuntu 12.04 machine. I have found <a href="https://stackoverflow.com/questions/23111631/cannot-download-docker-images-behind-a-proxy">this answer</a> but <code>systemctl</code> is not present in Ubuntu 12.04. How can I do this?</p>
  
  <p>Thanks.</p>