title: Unable to resolve 'us.archive.ubuntu.com' when using 'update' command in Ubuntu
body: <p>When I use the command "sudo apt-get update" I get the following errors:</p>
  
  <pre><code>   Err:1 http://us.archive.ubuntu.com/ubuntu bionic InRelease
       Could not resolve 'us.archive.ubuntu.com'
     Err:2 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease
       Could not resolve 'us.archive.ubuntu.com'
     Err:3 http://security.ubuntu.com/ubuntu bionic-security InRelease
       Could not resolve 'security.ubuntu.com'
     Err:4 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease
       Could not resolve 'us.archive.ubuntu.com'
     Reading package lists... Done
     W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/bionic      /InRelease  Could not resolve 'us.archive.ubuntu.com'
     W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/bionic-updates/InRelease  Could not resolve 'us.archive.ubuntu.com'
     W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/bionic-backports/InRelease  Could not resolve 'us.archive.ubuntu.com'
     W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/bionic-security/InRelease  Could not resolve 'security.ubuntu.com'
     W: Some index files failed to download. They have been ignored, or old ones used instead.
  </code></pre>
  
  <p>Could you please help me to solve it?</p>