Astrill Setup Manual:How to configure DNS on network adapter on Linux

http://askubuntu.com/questions/130452/how-do-i-add-a-dns-server-via-resolv-conf

http://www.liberiangeek.net/2012/05/setup-static-dns-servers-in-ubuntu-12-04-precise-pangolin/

http://lani78.wordpress.com/2012/07/22/setting-up-a-dns-for-the-local-network-on-the-ubuntu-12-04-precise-pangolin-server/

Ubuntu developers are very inconsistent, so many places for DNS resolver. Google is your best friend if you want to fix your DNS issues.