Nagios is a program that will monitor hosts and services on your
network. It has the ability to email or page you when a problem
arises and when a problem is resolved. Nagios is written in C and
is designed to run under Linux (and some other *NIX variants) as a
background process, intermittently running checks on various
services that you specify.

The actual service checks are performed by separate "plugin"
programs which return the status of the checks to Nagios.

This package provide core programs for nagios. The web interface,
documentation, and development files are built as separate
packages