If you've added another network card to Ubuntu Server, the way to enable it is:
First you need to find the name of the card
Try:
dmesg | grep -i network
You could also search for "eth" instead of "network"
In my case I have two:
[ 1.165623] e1000 0000:00:03.0: eth0: Intel(R) PRO/1000 Network Connection
[ 1.645478] e1000 0000:00:08.0: eth1: Intel(R) PRO/1000 Network Connection
named eth0 and eth1.
To see which is already in use and other info about your networking interfaces:
ifconfig
In my case eth0 is currently already configured, so I need to enable eth1
Edit /etc/network/interfaces, adding these lines:
auto eth1
iface eth1 inet dhcp
Then you can stop/start/restart networking with:
sudo /etc/init.d/networking start
sudo /etc/init.d/networking stop
sudo /etc/init.d/networking restart
For a static IP, add this to /etc/network/interfaces instead. (You'll need to figure out what the numbers should be somewhere else, but you could set it to use dhcp first and use ifconfig to get a clue as to what they should be.)
auto eth1
iface eth1 inet static
address 192.168.1.2
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
