Comment 2 for bug 1350811

The fault is not in the S. O. , is a fault of the environment graphic MATE 1.8 . From -> Ubuntu 12.04 » Ubuntu Server Guide » Networking »:

The most notable difference for the user is that any change manually done to /etc/resolv.conf will be lost as it
gets overwritten each time something triggers resolvconf. Instead, resolvconf uses DHCP client hooks, and /etc/network/interfaces to generate a list of nameservers and domains to put in /etc/resolv.conf, which is now a symlink:

/etc/resolv.conf -> ../run/resolvconf/resolv.conf

To configure the resolver, add the IP addresses of the nameservers that are appropriate for your network in the file
/etc/network/interfaces.

You can close this bug.
Thanks.