Error failed sudo apt-get update

user@ubuntu-server:~$ sudo apt-get update
Err:1 http://us.archive.ubuntu.com/ubuntu xenial InRelease
  Temporary failure resolving 'us.archive.ubuntu.com'
Err:2 http://security.ubuntu.com/ubuntu xenial-security InRelease
  Temporary failure resolving 'security.ubuntu.com'
Err:3 http://ppa.launchpad.net/ondrej/php5/ubuntu xenial InRelease
  Temporary failure resolving 'ppa.launchpad.net'
Err:4 http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease
  Temporary failure resolving 'us.archive.ubuntu.com'
Err:5 http://us.archive.ubuntu.com/ubuntu xenial-backports InRelease
  Temporary failure resolving 'us.archive.ubuntu.com'
Reading package lists... Done
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial/InRelease  Temporary failure resolving 'us.archive.ubuntu.com'
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial-updates/InRelease  Temporary failure resolving 'us.archive.ubuntu.com'
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial-backports/InRelease  Temporary failure resolving 'us.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://ppa.launchpad.net/ondrej/php5/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.
user@ubuntu-server:~$