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.
Open up the /etc/network/interfaces file. I’m going to use vi, but you can choose a different editor
sudo vi /etc/network/interfaces
For the primary interface, which is usually eth0, you will see these lines:
auto eth0 iface eth0 inet dhcp
We are going to change dhcp to static, and then there are a number of options that should be added below it. You will need to 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 vi /etc/resolv.conf
On the line ‘name server 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)
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.