Ubuntu loses network connection after do-release-upgrade - Ignoring unknown interface eth0=eth0

Over the weekend I decided to upgrade one of my linux servers, running an Ubuntu desktop. The Ubuntu do-release-upgrade tool is pretty reliable, even over SSH the whole process completed without any errors (try that from Windows 2003 - 2008). The only issue is that after reboot the machine disappeared from the net. Had to hack into the console to have a look what's going on. Turns out my eth0 interface wasn't configured so didn't get any IP addresses:

> ifup eth0
 * Reconfiguring network interfaces... Ignoring unknown interface eth0=eth0.

The fix was pretty easy, just had to edit /etc/network/interfaces files and try again:

auto lo
iface lo inet loopback
# For DHCP only
auto eth0
# Statis IP assignment
iface eth0 inet static
address 79.1.2.3
netmask 255.255.255.0
gateway 79.1.2.1
# Google's DNS - fast and reliable
dns-nameservers 8.8.8.8

ifup eth0 was much friendlier this time, the box was back on the net again.

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