This only concerns when the resolvconf package is installed
sudo cp -p head head.orig #backup copy, always do this
sudo nano head
The top of the file is a scary warning. The file /etc/resolv.conf is autogenerated from the contents of this file; the warning is there so it will get put in /etc/resolv.conf when /etc/resolv.conf is generated.
To the end of the file, add (IP of DNS server):
Press Ctrl x and answer yes to saving the file. To finish up, regenerate /etc/resolv.conf so the changes are applied right now:
sudo resolvconf -u