Ubuntu Ethernet Configuration

First, verify that you have a valid ethernet interface; ideally eth0:
See if you can connect temporarily:
sudo dhclient eth0
If you connect, edit /etc/network/interfaces to set a static IP address appropriate for a server:
sudo vim /etc/network/interfaces
I suggest the following, adjusted, of course to suit your network:
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
Save the file and quit vim. Be sure to use an IP address outside the range of the DHCP pool in the router so as to avoid collisions. Get the system to read and use the changes:
sudo ifdown eth0 && sudo ifup -v eth0
ping -c3 www.google.com
If you get ping returns, you are all set.