Install Request Tracker
Since covering an install of Request Tracker 4 on Debian (Part 1/2, 2/2), my most common request has been a guide for Ubuntu. A lot of the material is the same, since Ubuntu is a derivative of Debian.
This guide assumes you are installing a fresh install of Ubuntu 12.04 LTS Server onto a new computer or virtual machine. I have chosen the latest LTS release as it will be supported for far longer than regular releases. These instruction should also work on any version of Ubuntu released after 11.10 (minor changes may be required).