root@1da693ad87d6:/# apt-get update
Err:1 http://ppa.launchpad.net/nginx/stable/ubuntu xenial InRelease
  Temporary failure resolving 'ppa.launchpad.net'
Err:2 http://archive.ubuntu.com/ubuntu xenial InRelease
  Temporary failure resolving 'archive.ubuntu.com'
Err:3 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
  Temporary failure resolving 'archive.ubuntu.com'
Err:4 http://archive.ubuntu.com/ubuntu xenial-security 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-security/InRelease  Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://ppa.launchpad.net/nginx/stable/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.
root@1da693ad87d6:/# cat /etc/debian_version
stretch/sid