Xmodule posted a tutorial about monitor Linux servers with SNMP and Cacti

SNMP (or Simple Network Management Protocol) is used to gather data on what is going on within a device such as load, hard disk states, bandwidth. These data are used by network monitoring tools such as Cacti to generate graphs for monitoring purposes.

In a typical deployment of Cacti and SNMP, there will be one or more SNMP-enabled devices, as well as a separate monitoring server where Cacti collects SNMP feeds from those devices. Please keep in mind that all the devices that need to be monitored must be SNMP enabled. In this tutorial, we will be configuring Cacti and SNMP in the same Linux server for demonstration purpose

  How to monitor Linux servers with SNMP and Cacti