The following sections if followed, will ensure that you end up with an extremely secure system.

Introduction

Decisions to Make

Install the Base Ubuntu System

First Configuration

Initial Configuration

Base Security

Add Software

https://ubuntuforums.org/showthread.php?t=1983344

The CIS benchmarks recommendations for hardening the system.

http://benchmarks.cisecurity.org/en-us/?route=downloads.benchmarks

https://www.thefanclub.co.za/how-to/how-secure-ubuntu-1604-lts-server-part-1-basics

debsums http://ubuntuforums.org/showthread.php?t=2225059

http://manpages.ubuntu.com/manpages/xenial/man1/debsums.1.html

/etc/issue

https://www.digitalocean.com/community/tutorials/7-security-measures-to-protect-your-servers