HowTo: Fix networking not working after installing Ubuntu Desktop from a PXE-booted Live Environment

by HyRax June 14, 2012

Scenario: You’ve setup a PXE server. You’ve setup an Ubuntu Live CD to boot over your network via PXE. Everything works well.

You then decide to install a fresh Ubuntu Desktop installation from your PXE-booted environment. All goes well. The install finishes and your system reboots.

When the system comes up, you discover that there’s no network connections. Ethernet doesn’t work, but wifi probably is working OK, or you can’t get wifi working yet because you need to install a closed-source driver for it. You check the Network Manager and find that there is no automatically defined ethernet connection such as “Auto eth0″. What’s the go?

Here’s how to fix it.

When you run a PXE environment, one of the key things that has to be configured before any startup commenced is your IP address. This is performed by your PXE agent and means that when the Ubuntu Live Environment boots up, DHCP is not employed during bootup because it would sever your connection to your NFS server where the Ubuntu Live Environment is booting from.

As a result of this, when you install from the PXE-booted Live Environment, which is effectively a direct copy of the Live Environment, you also end up copying the manually-configured network setup where Network Manager is essentially told not to do anything.

So let’s fix that.

Once your system is installed and rebooted for the first time, open yourself a Terminal window.
Type in the following:

$ sudo nano /etc/network/interfaces

…and hit Enter.
You will see an entry for eth0 there looking something like this:

auto eth0
iface eth0 inet manual
Since Ubuntu uses Network Manager to manage network connections, any definition listed in this file will automatically override it, so simply delete the “iface” line underneath “auto eth0″, but leave the “auto eth0″ line intact.
Save your changes by pressing CTRL+X, then Y and then Enter.
Restart your PC.
Upon restarting, your system should now show a working ethernet connection as normal with all connectivity restored.
Pat yourself on the back. You are done.