nagios: nagios (Host/service/network monitoring program)
nagios: 
nagios: Nagios is a program that will monitor hosts and services on your
nagios: network. It has the ability to email or page you when a problem arises
nagios: and when a problem is resolved. Nagios is written in C and is
nagios: designed to run under Linux (and some other *NIX variants) as a
nagios: background process, intermittently running checks on various services
nagios: that you specify.
nagios:
nagios: The actual service checks are performed by separate "plugin" programs
nagios: in package nagios-plugins.