Scenario: You have a box running Ubuntu Server. Something happens to the box and you decide to move the hard-drive to another physical machine to get the server back up and running. The hardware is identical on the other machine, so there shouldn't be any issues at all, right? The machine starts up fine, but when you try and hit the network, you can't. Closer inspection using the ifconfig command reveals that there is no "eth0? adapter configured. Why? Here's how to fix it. Ubuntu Server keeps tabs on the MAC address of the configured ethernet adapter. Unlike Ubuntu Desktop, you can't simply change network cards willy nilly -- while Ubuntu Server does detect and automatically setup new cards, it won't automatically replace any adapter already configured as eth0 with another one, so you need to tell Ubuntu Server that you no longer need the old adapter. This problem can also appear if you have a virtual machine such as one from Virtualbox, and you move or copy it from one host to another without ensuring that the MAC address configured for that VM's ethernet adapter is 100% identical to the previous one. These instructions were done with Ubuntu Server 9.04 Jaunty Jackalope in mind, but should apply to just about any release. Since you can't SSH in, you will need to login directly on the Ubuntu Server console as an appropriate user with sudo rights. . Once logged in, type in the following and hit Enter: $ sudo nano