MRTG

Introduction
The Multi Router Traffic Grapher, or just simply MRTG, is free software for monitoring and measuring the traffic load on network links. It allows the user to see traffic load on a network over time in graphical form.

HOWTO: Install On Ubuntu Server
https://www.iceflatline.com/2009/08/how-to-install-and-configure-mrtg-on-ubuntu-server/