title: Ubuntu lightdm.service does not exist
body: <p>Not able to login Ubuntu from GUI but console is fine. Then I tried</p>
  
  <pre><code>systemctl start lightdm
  </code></pre>
  
  <p>It shows</p>
  
  <pre><code>Unit lightdm.service not found.
  </code></pre>
  
  <p>After reinstalling lightdm, got same result: lightdm.service not found</p>
  
  <p>Ubuntu I'm using should be the newest version which I downloaded yesterday.(Oct30/2018)</p>
  
  <p>Not sure what's going wrong, any suggestions?</p>