title: Running docker container with ubuntu:16.04 actually runs ubuntu 18.04
body: <p>I was trying to run a docker container with ubuntu:16.04 (on a ubuntu 18.04 machine) with the following command:</p>
  
  <pre><code>docker run -i -t --name ubuntu ubuntu:16.04 /bin/bash
  </code></pre>
  
  <p>Running this command attaches me to a container. But when I check the kernel information with <code>uname -a</code>, it shows that the current kernel is Ubuntu 18.04.  Following is the result I get:</p>
  
  <pre><code>Linux 1ac6c3456e2a 5.3.0-40-generic #32~18.04.1-Ubuntu SMP Mon Feb 3 14:05:59 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
  </code></pre>
  
  <p>What could be the cause?</p>