Ubuntu Server 10.04
Upgraded by "do-release-upgrade"
Ubuntu Server 12.04
ISPconfig 3 v.18.104.22.168
By accident, almost, I upgraded to Ubuntu Server 12.04.
I did this before the ISPconfig3 installation. But, I followed the tutorial "The Perfect Server - Ubuntu 10.04" not knowing that I actually had an Ubuntu 12.04 installation. I found some of the differenses such as /etc/network/interfaces where I added the nameservers according to the tutorial for Ubuntu 12.04. Still I'm wondering if there is other things to be corrected. If there's someone who also upgraded his/her server, please don't hesitate to inform me