Changing network settings in new versions of Ubuntu (don’t know when exactly this new methodology started) like Ubuntu 12.04 Precise Server Edition, has a major difference from the old methodology.
The major change is that you no longer need to edit “/etc/resolv.conf”, and if you try to, your settings will be lost or overwritten once you reboot.
All what you need to change if you want to apply a static address (which is the case in almost all server installations) is the “/etc/network/interfaces” file.
iface eth0 inet static
dns-nameservers xx.xx.xx.xx xx.xx.xx.xx xx.xx.xx.xx
You will notice that everything is the same, except the last line which used to be added to the /etc/resolv.conf directly before. With this new methodology the “resolvconf” utility will automatically read the “dns-nameservers” one by one (separated by a space) and will append them to the “etc/resolv.conf” file.
After that to apply your changes, you can just do “sudo /etc/init.d/networking restart” or simply reboot your machine if you wish.