Nagios Wiki

Nagios:  is a popular open source computer system and network monitoring software application. It watches hosts and services, alerting.

 Monitoring of network services (SMTP, POP3, HTTP, NNTP, PING, etc.)

 Monitoring of host resources (processor load, disk and memory usage, running processes, log files, etc.)

All the hard work is done by plugins, the nagios daemon «only» schedules them to be executed at the right time with the right parameters and collect results.


The cgi interface is entirely optional, but highly useful.


Nagios Operation

The nagios daemon

• schedules and executes active host and service checks
• accepts asyncronous passive checks
• sends out notifications on host or service state change
• executes event handlers on host or service state change
• writes and rotates log and state files


Nagios Operation Local Plugin Execution


 All active checks involve the local execution of some plugin. Locally executed plugins can just check for some local service or then can go to the network and check some remote host or service. NRPE allows execution of plugins on remote hosts. Remote plugin results are reported to nagios by the locally executed check_nrpe plugin.

Distributed Monitoring

Nagios can be configured to support distributed monitoring of network services and resources. The goal in the distributed monitoring environment that I will describe is to offload the overhead (CPU usage, etc.) of performing service checks from a "central" server onto one or more "distributed" servers. When you want to start monitoring hundreds or even thousands of hosts (and several times that many services) using Nagios, this becomes quite important. A distributed solution is often called a master/slave solution. On the master you have a copy of every service that you want to check on the slaves, but the copy on the master has the active check disabled and notification enabled, while on the slaves both active and passive checks are enabled and notification is disabled.

nagios.cfg – contains options for daemon behaviour
cgi.cfg – controls the web interface
resource.cfg – tells nagios where to look for plugins

Check configuration with nagios -v nagios.cfg

# File locations
log_file=/var/log/nagios.log
cfg_file=/etc/opt/nagios/checkcommands.cfg
cfg_file=/etc/opt/nagios/misccommands.cfg
cfg_file=/etc/opt/nagios/host.cfg
resource_/etc/opt/nagios/resource.cfg
lock_file=/var/run/nagios.lock

The NRPE addon is designed to allow you to execute Nagios plugins on 
remote Linux/Unix machines. This allow Nagios to monitor "local" 
resources (like CPU load, memory usage, etc.) on remote machines

The NRPE addon consists of two pieces:

The check_nrpe plugin, which resides on the local monitoring machine
The NRPE daemon, which runs on the remote Linux/Unix machine

When Nagios needs to monitor a resource of service from a remote Linux/Unix machine:

Nagios will execute the check_nrpe plugin and tell it what service needs to be checked
The check_nrpe plugin contacts the NRPE daemon on the remote host over an (optionally) SSL-protected
connection

The NRPE daemon runs the appropriate Nagios plugin to check the service or resource
The results from the service check are passed from the NRPE daemon back to the check_nrpe plugin, which
then returns the check results to the Nagios process.
Note: The NRPE daemon requires that Nagios plugins be installed on the remote Linux/Unix host. Without these,
the daemon wouldn't be able to monitor anything.

http://www.softpanorama.org/Admin/Monitoring/nagios.shtml