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As the questioner gives the contents of his /etc/network/interfaces I infer that he is using ifup to configure interfaces. But since he may actually be using NetworkManager, I will discuss that as well.

If you are using ifup then DNS settings go in /etc/network/interfaces. For each interface you add dns-* options appropriate for the nameserver(s) available over that interface. E.g., if a nameserver at address 1.2.3.4 is available over interface eth0, then add dns-nameservers 1.2.3.4 to the iface eth0 stanza.

If you are using NetworkManager then settings are entered in the Connection Editor (network indicator | Edit Connections...) in the IPv4 Settings tab.

Doing /etc/init.d/networking restart to reconfigure interfaces is deprecated. If you are using ifup then first ifdown each active network interface, then ifup each interface. If you are using NetworkManager then, first, disable networking using the indicator (top of the desktop); then open a terminal and run

sudo restart network-manager

and then enable networking using the indicator.

Or you can just reboot.

Regarding the fact that /etc/init.d/networking restart resulted in

RTNETLINK answers: File exists

Failed to bring up eth0  

This means that ifupdown thinks that eth0 is already up. Use ifdown --force eth0 to cause ifupdown to stop believing that it has already configured the interface.

Regarding the "deprecated" message, this message is no longer printed in Ubuntu 12.10 but you should still note that initscripts are "on their way out". To restart a service foo, use service foo restart or restart foo. Note also that if you want to reconfigure your interfaces it is better to ifdown them one by one than to rely on restarting "networking".

If none of the above work, keep it mind that Ubuntu appends a tail file to the resolv.conf file that it generates.

Try this:

sudo nano /etc/resolvconf/resolv.conf.d/tail

Which will open a blank resolv.conf.d file in the nano text editor. You will need to place your DNS server address on the first line of this file and remember to end the line with a carriage return (hit enter) as seen below:

nameserver 10.20.1.2

Editing the tail file instead of the actual resolv.conf file will prevent your change from being lost upon a system reboot.

You will need to run sudo resolvconf -u to activate the change. You should be able to ping google.com after this. Good luck!

Command line version:

You should add your nameserver(s) to /etc/resolvconf/resolv.conf.d/base file this way:

nameserver 66.212.63.228 

nameserver 66.212.48.10

All of the answers which relate to /etc/network/interfaces incorrectly state dns-nameservers rather than dns-nameserver - below should work:

auto wlan0

iface wlan0 inet static

address 192.168.1.28

netmask 255.255.255.0

gateway 192.168.1.1

dns-nameserver 8.8.8.8

dns-nameserver 8.8.4.4

dns-search something.network.com

(tested on Ubuntu 15.04)

Easiest method of configuring your DNS servers is to use NetworkManager

Under IPv4, fill in your dns server(s)

I was able to work around this on a headless ubuntu server install by adding

nameserver 8.8.8.8

...after the relevant interface stuff in /etc/network/interfaces:

auto wlan0

iface wlan0 inet static

address 192.168.1.28

netmask 255.255.255.0

gateway 192.168.1.1

dns-nameservers 8.8.8.8

dns-nameservers 8.8.4.4

Hope this helps later users!

Note: carefull using without direct access on the machine, this will cut the connection...

I use

sudo ifdown eth0

then

sudo ifup eth0

It will reset and release everything...

If it faces with errors related to configuration, you can use:

sudo ifdown eth0 --force

This worked for me

sudo vi /etc/resolvconf/resolv.conf.d/base

and add:

nameserver <add your router ip>

Run:

sudo resolvconf -u

I use core install of ubuntu server.

You are missing a subnet specification in the interfaces file.

Add netmask 255.255.255.0 to /etc/network/interfaces below the network line.

For some reason the dns-nameservers statement does nothing in my case. And the other answers are not by the book, as they bypass dnsmasq as it is utilized in Ubuntu.

To do this right, edit /etc/dnsmasq.conf

Add your nameservers to the bottom of the file:

server=8.8.8.8

server=8.8.4.4

Restart dnsmasq to use the new settings:
sudo service dnsmasq restart

Credit: https://unix.stackexchange.com/a/163506/187949

You might configure that interface in an other file too, since you have more gateways.

Details are here.