5 best free and open source system monitoring tools

1. Nagios

Nagios is a powerful, enterprise-class host, service, application, and network monitoring program. Designed to be fast, flexible, and rock-solid stable. Nagios runs on *NIX hosts and can monitor Windows, Linux/Unix/BSD, Netware, and network devices.

2. Cacti

Cacti is a web-based network monitoring and graphing tool designed as a front-end application. Cacti uses RRDtool for the network graphing solution. Using Cacti you can monitor and graph – CPU Load, Network bandwidth utilization, network traffic monitor etc. Cacti also supports plugin architecture.

3. NTop

Ntop is a tool for both Unix and Win32 that shows the network usage, similar to what the popular top Unix command does. It sports a web interface for accessing accounting data and includes support for popular tools/protocols as well DPI and host categorization.

4. Zabbix

ZABBIX is an enterprise-class open source distributed monitoring solution designed to monitor and track performance and availability of network servers, devices and other IT resources. It supports distributed and WEB monitoring, auto-discovery, and more.

5. Munin

Munin the monitoring tool surveys all your computers and remembers what it saw. It presents all the information in graphs through a web interface. Its emphasis is on plug and play capabilities. It  Master/node to gather and graph "everything" on your systems using Tobi Oetiker's rrdtool. It can optionally warn your surveillance software. This software package was originally called LRRD.