Unity HUD Errors

Issue

Unity under Ubuntu 12.04 issues errors to the effect of "HUD Service not running". This usually arises after a user update from 10.04 to 12.04, with the vanilla Precise Pangolin image. Pressing the Alt key brings up the HUD and can accept input, but doesn't show any options nor can be interacted with in any other way.

Solution

A package is missing that provides the backend for the HUD service. Booted (or chrooted) into the 12.04 environment, run the following:

 sudo apt-get install indicator-appmenu-tools

No reboot should be necessary.