sudo apt update
Err http://us.archive.ubuntu.com trusty InRelease

Err http://security.ubuntu.com trusty-security InRelease

Err http://us.archive.ubuntu.com trusty-updates InRelease

Err http://us.archive.ubuntu.com trusty-backports InRelease

Err http://security.ubuntu.com trusty-security Release.gpg
  Could not resolve 'security.ubuntu.com'
Err http://us.archive.ubuntu.com trusty Release.gpg
  Could not resolve 'us.archive.ubuntu.com'
Err http://us.archive.ubuntu.com trusty-updates Release.gpg
  Could not resolve 'us.archive.ubuntu.com'
Err http://us.archive.ubuntu.com trusty-backports Release.gpg
  Could not resolve 'us.archive.ubuntu.com'
Reading package lists... Done
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty/InRelease

W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-updates/InRelease

W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-backports/InRelease

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/InRelease

W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty/Release.gpg  Could not resolve 'us.archive.ubuntu.com'

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/Release.gpg  Could not resolve 'security.ubuntu.com'

W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-updates/Release.gpg  Could not resolve 'us.archive.ubuntu.com'

W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-backports/Release.gpg  Could not resolve 'us.archive.ubuntu.com'

W: Some index files failed to download. They have been ignored, or old ones used instead.