Ok.
Since we now know that the WebUI starts when you fire it up manually, we know it works. It is just the autostart feature that do not fire.
Have you tried this (from HOW TO: install MINEOS-NODE on UBUNTU SERVER 14.04.2):
AUTOMATIC/ START ON BOOT COMMANDS-
sudo cp /usr/games/minecraft/init/upstart_conf /etc/init/mineos.conf
sudo start mineos
This is for an Ubuntu Server 14.04.2 clean install, so your OS may have other commands for adding to the autostart-feature. Did you download one of the precompiled MineOS images and install from scratch? Or did you install a linux-version first, then added MineOS ?