host/service/network monitoring and management system core files

 Nagios is a monitoring and management system for hosts, services and
 networks. The package contains the nagios4 monitoring daemon.
 .
 Nagios' features include:
 .
  * Monitoring of network services (via TCP port, SMTP, POP3, HTTP, NNTP,
     PING, etc.)
  * Plugin interface to allow for user-developed service checks
  * Contact notifications when 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)
  * Web output (current status, notifications, problem history, log file, etc.)