Ubuntu Geek shows you how to install Nagios 4.0.1 in Ubuntu 13.10 server

Nagios® Core™ is an Open Source system and network monitoring application. It watches hosts and services that you specify, alerting you when things go bad and when they get better.Nagios Core was originally designed to run under Linux, although it should work under most other unices as well.

Some of the many features of Nagios Core include:

Monitoring of network services (SMTP, POP3, HTTP, NNTP, PING, etc.)
Monitoring of host resources (processor load, disk usage, etc.)
Simple plugin design that allows users to easily develop their own service checks
Parallelized service checks
Ability to define network host hierarchy using "parent" hosts, allowing detection of and distinction between hosts that are down and those that are unreachable
Contact notifications when service or host problems occur and get resolved (via email, pager, or user-defined method)
Ability to define event handlers to be run during service or host events for proactive problem resolution
Automatic log file rotation
Support for implementing redundant monitoring hosts

  How to install Nagios 4.0.1 (Monitoring Tool) in ubuntu 13.10 server (Saucy Salamander)