Comment 25 for bug 900903

Yeah, though in this case I don't see how we could have automatically detected it.

The initial installation (based on kernel versions) was Ubuntu 8.04 which apparently was still writing interface entries in /etc/network/interfaces even when using Network Manager (we don't do that anymore).

Now, to be able to automatically migrate that configuration to its current equivalent (which is to only have the loopback device in /etc/network/interfaces), we'd need to have a way to know whether the user actually meant for eth0 to be in /etc/network/interfaces which is a supported use case currently interpreted by Network Manager as "don't touch this interface and let ifupdown deal with it".

I'm not completely sure as I don't have any desktop install of Ubuntu 8.04 around (end of support) but I guess if we wanted to fix this issue we would have needed to put some magic in the 8.04 => 8.10 and 8.04 => 10.04 upgrader, potentially looking at the installer debconf database or the install log to figure out whether the current /etc/network/interfaces is the result of the installer or the result of someone manually disabling Network Manager.