title: Signatures couldn't be verified because the public key is not available error while installing docker
body: <p>Unable to install docker with:  </p>
  
  <pre><code>sudo sh -c "echo deb https://get.docker.com/ubuntu docker main &gt; /etc/apt/sources.list.d/docker.list"
  </code></pre>
  
  <p>error log:</p>
  
  <blockquote>
    <p>GPG error: <a href="https://get.docker.com" rel="noreferrer">https://get.docker.com</a> docker Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D8576A8BA88D21E9</p>
  </blockquote>