If the Ubuntu Server installer has set your server to use DHCP, you will want to change it to a static IP address so that people can actually use it.
Changing this setting without a GUI will require some text editing, but that's classic linux, right?
Let's open up the /etc/network/interfaces file. I'm going to use nano, but you can choose a different editor.
sudo nano /etc/network/interfaces
For the primary interface, which is usually eth0, you will see these lines:
auto eth0 iface eth0 inet dhcp
As you can see, it's using DHCP right now. We are going to change dhcp to static, and then there are a number of options that should be added below it. Obviously you'd customize this to your network.
auto eth0
iface eth0 inet static
address 192.168.1.100
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
gateway 192.168.1.1
Now we'll need to add in the DNS settings by editing the resolv.conf file:
sudo nano /etc/resolv.conf
On the line 'nameserver xxx.xxx.xxx.xxx' replace the x with the IP of your name server. (You can do ifconfig /all to find out what they are)
You need to also remove the dhcp client for this to stick (thanks to Peter for noticing). You might need to remove dhcp-client3 instead.
sudo apt-get remove dhcp-client<br /> //OR_<br /> sudo apt-get remove isc-dhcp-client
Now we'll just need to restart the networking components:
sudo /etc/init.d/networking restart
Ping www.google.com. If you get a response, name resolution is working(unless of course if google is in your hosts file).
To temporarily do this run:<br />
ifconfig eth1 promisc
If you want to make it permanent, edit /etc/network/interfaces
auto eth1
iface eth1 inet manual
up ifconfig $IFACE 0.0.0.0 up
up ip link set $IFACE promisc on
down ip link set $IFACE promisc off
down ifconfig $IFACE down