root@server1:~# sudo apt-get update
Err:1 http://apt.izzysoft.de/ubuntu generic InRelease
  Temporary failure resolving 'apt.izzysoft.de'
Err:2 http://ppa.launchpad.net/ondrej/apache2/ubuntu xenial InRelease
  Temporary failure resolving 'ppa.launchpad.net'
Err:3 http://apt.newrelic.com/debian newrelic InRelease
  Temporary failure resolving 'apt.newrelic.com'
Err:4 http://software.virtualmin.com/gpl/ubuntu virtualmin-xenial InRelease
  Temporary failure resolving 'software.virtualmin.com'
Err:5 http://ppa.launchpad.net/ondrej/php/ubuntu xenial InRelease
  Temporary failure resolving 'ppa.launchpad.net'
Err:6 http://security.ubuntu.com/ubuntu xenial-security InRelease
  Temporary failure resolving 'security.ubuntu.com'
Err:7 http://software.virtualmin.com/gpl/ubuntu virtualmin-universal InRelease
  Temporary failure resolving 'software.virtualmin.com'
Err:8 http://archive.ubuntu.com/ubuntu xenial InRelease
  Temporary failure resolving 'archive.ubuntu.com'
Err:9 https://deb.nodesource.com/node_4.x xenial InRelease
  Could not resolve host: deb.nodesource.com
Err:10 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
  Temporary failure resolving 'archive.ubuntu.com'
Err:11 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
  Temporary failure resolving 'archive.ubuntu.com'
Reading package lists... Done
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial/InRelease  Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-updates/InRelease  Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-backports/InRelease  Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/InRelease  Temporary failure resolving 'security.ubuntu.com'
W: Failed to fetch http://software.virtualmin.com/gpl/ubuntu/dists/virtualmin-xenial/InRelease  Temporary failure resolving 'software.virtualmin.com'
W: Failed to fetch http://software.virtualmin.com/gpl/ubuntu/dists/virtualmin-universal/InRelease  Temporary failure resolving 'software.virtualmin.com'
W: Failed to fetch http://apt.izzysoft.de/ubuntu/dists/generic/InRelease  Temporary failure resolving 'apt.izzysoft.de'
W: Failed to fetch http://apt.newrelic.com/debian/dists/newrelic/InRelease  Temporary failure resolving 'apt.newrelic.com'
W: Failed to fetch https://deb.nodesource.com/node_4.x/dists/xenial/InRelease  Could not resolve host: deb.nodesource.com
W: Failed to fetch http://ppa.launchpad.net/ondrej/apache2/ubuntu/dists/xenial/InRelease  Temporary failure resolving 'ppa.launchpad.net'
W: Failed to fetch http://ppa.launchpad.net/ondrej/php/ubuntu/dists/xenial/InRelease  Temporary failure resolving 'ppa.launchpad.net'
W: Some index files failed to download. They have been ignored, or old ones used instead.