You will need to edit this file with your favorite editor:

sudo vim /etc/dhcp/dhclient.conf

Once in file, you should see a commented line with the word supersede next to it:

#supersede domain-name "...."

Uncomment that line, substitute the name supersede for append, then add the domain names you wish to search (follow the example below and leave a space after the first "):

append domain-name " ubuntu.com ubuntu.net test.ubunut.com";

Save the file and close.

All you need to do is restart your network connection. You can do this by unplugging and plugging in the physical network connect OR disable and enable your network connect (see picture below). After that you should be good to go:

To verify:

sudo cat /etc/resolv.conf

Disconnect Network

Connect Network