Now that Ubuntu 9.04 (Jaunty Jackalope) is out I decided to upgrade a few of my servers from 8.10 (Intrepid Ibex) to the latest release. To upgrade via the command line follow these steps (as root or via sudo):

aptitude update
aptitude safe-upgrade
aptitude install update-manager-core

This will get your system upgraded to the latest packages of 8.10 and install the scripts to move to Jaunty. Be sure you have screen installed as well – Ubuntu does not like having upgrades interrupted so you want to be able to resume if your session is interrupted for any reason.

screen do-release-upgrade

It will download and check a few things and then warn you about operating an upgrade over ssh (along with starting an extra ssh daemon on port 9004). Simply follow the instructions from there and you’ll have a fully upgraded server!1

cat /etc/lsb-release
  1. Bear in mind that during the upgrade you will occasionally be asked questions about config files, so don’t try to run this upgrade unattended.