Why is my USB Ethernet Card not working in Ubuntu 14.04 Server?

Question

I've got a laptop which I'm trying to set up as a server (a rebadged Uniwill 223ii0), but it has an ethernet port which is dodgy (sometimes works, sometimes doesn't).

I bought a £20 usb ethernet card which worked out of the box when the laptop was running Windows 7, and worked during the server install, but not once the server was standing on its own two feet, as it tries to get network configuration on boot, then waits another minute before giving up and completing the boot.

Once logged in, using sudo ifup eth2 yields that it is already configured, so bringing the adapter down and up yields with a long DHCPDISCOVER sequence which yields that "the network is down".

I am using the adapter on my Windows 7 machine right now to write this, and the same cable in the dodgy port on the laptop is working, for now

Any ideas?

Solution

Huh, looks like I found a bug with the way 14.04 is installed.

It turns out that whilst my USB card was eth2 on install, it got reassigned eth1 afterward, and the system tried to connect on eth2 (whatever eth2 may be, unless the onboard modem or wireless card counts as an ethernet interface).

Replacing eth2 with eth1 in /etc/network/interfaces and bringing up the adapter with sudo ifup eth1 solved this for me