title: How to start Docker daemon on Ubuntu?
body: <p>On Windows, I've always been able to build Docker images with no problems. </p>
  
  <p>I'm now trying to build a simple Docker image on Ubuntu 18.04 and typing in the terminal: </p>
  
  <pre><code>sudo docker build -t test .
  </code></pre>
  
  <p>results in the following error: </p>
  
  <pre><code>Cannot connect to the Docker daemon at unix:///var/run/docker.sock. 
  Is the docker daemon running?
  </code></pre>
  
  <p>How do I start the Docker daemon? I want to be able to build the image successfully</p>
  
  <p><strong>EDIT:</strong> </p>
  
  <p>Typing <code>sudo systemctl start docker</code> as stated in the original documentation <a href="https://docs.docker.com/config/daemon/systemd/" rel="noreferrer">https://docs.docker.com/config/daemon/systemd/</a> results in the following error: </p>
  
  <pre><code>Failed to start docker.service: Unit docker.service is masked.
  </code></pre>