A step by step guide for Ubuntu 16.04 which explains how to :

1. Install Snort
2. Replace with Emerging Threats rules
3. Configure Oinkmaster for automatic updates
4. Start snort and view analytics in TrisulNSM

Snort has a package for Ubuntu. This installs all components required.

apt-get update
apt-get install snort

Also install oinkmaster , which also has an Ubuntu package

apt-get install oinkmaster

We like the ET and ET Pro rulesets for a number of reasons. If you wish to remain with the Snort community rules or move to the excellent Talos ruleset, you can skip this step.

cd /etc/snort
mv rules rules_old
wget https://rules.emergingthreats.net/open/snort-2.9.0/emerging.rules.tar.gz
tar xf emerging.rules.tar.gz -C /etc/snort 

Open snort.conf and copy the lines from rules/emerging.conf into snort.conf and comment out the old snort.conf rules.

Next specify a HOMENET, otherwise many ET rules wont load

Example:

ipvar HOME_NET 192.168.0.0/16,10.0.0.0/8