nagios2

Start nagios2

$ nagios2 /etc/nagios2/nagios.cfg

$ nagios2 -d

$ nagios2 -s

$ nagios2 -v

nagios [-c <config_file>] [-d] [-v] [-s] [-u <user>] [-g <group>] [-p <pid_file>] [-x <debug_level>] [-V]

-c <config_file>
    Specifies an alternative main configuration file to use instead of the default (`nagios.cfg`).

-d
    Runs the Nagios daemon in the background. This is the typical mode of operation for continuous monitoring.

-v
    Verifies the configuration files for syntax errors, logical issues, and duplicate definitions, then exits. Highly recommended before starting or restarting.

-s
    Displays program status information to standard output (if compiled with status output support), useful for debugging.

-u <user>
    Runs the Nagios daemon as the specified unprivileged user after initialization. Improves security.

-g <group>
    Runs the Nagios daemon as the specified unprivileged group after initialization. Improves security.

-p <pid_file>
    Specifies an alternative PID file path for the daemon. The PID file contains the process ID of the running Nagios instance.

-x <debug_level>
    Sets the debug level for the daemon, allowing more verbose logging for troubleshooting. Higher numbers mean more detail.

-V
    Prints the Nagios Core version information and exits, useful for verifying the installed version.

The nagios command primarily refers to the Nagios Core daemon, the heart of the Nagios IT infrastructure monitoring system. While "nagios2" specifically implies version 2.x of this system, the core daemon command itself is typically nagios. It runs in the background, continuously checking the health of hosts, services, and network devices based on predefined configuration files. Nagios uses plugins to execute checks, processing their output to determine the status (OK, WARNING, CRITICAL, UNKNOWN) and triggering notifications or event handlers when issues are detected. It's a foundational tool for proactive system administration, helping identify and resolve problems before they impact users. Its modular design allows extensive customization and integration with various IT environments.

Nagios Core, especially older versions like 2.x, requires significant manual configuration through text files, which can be complex and error-prone for large environments. While powerful, its setup and maintenance demand a deep understanding of its configuration syntax and monitoring principles. It lacks a built-in discovery mechanism, requiring all hosts and services to be manually defined. Performance can become a concern with thousands of checks, and alert fatigue is a common issue if notifications are not carefully managed. Newer versions (Nagios 4.x) offer improvements, but the core configuration paradigm remains similar.

Nagios relies heavily on plain-text configuration files, typically located in /usr/local/nagios/etc/ or /etc/nagios/. These files define hosts, hostgroups, services, servicegroups, contacts, timeperiods, and commands, dictating exactly what to monitor and how.

Nagios Core includes a basic web interface (CGI-based) for viewing current status, history, reports, and managing downtime. It provides a centralized dashboard for monitoring all configured items and is accessible via a web browser.

The Nagios project began in 1999 as "NetSaint" by Ethan Galstad. It was renamed "Nagios" (a recursive acronym for "Nagios Ain't Gonna Insist On Sainthood") in 2002 due to trademark issues. Nagios 2.x, released around 2004-2005, significantly improved upon its predecessors with features like distributed monitoring capabilities and enhanced event handling. This version was widely adopted and formed the basis for many monitoring setups for years. Development continued with Nagios 3.x (2007) and currently Nagios 4.x (2013 onwards), each bringing further scalability, performance, and user interface enhancements while maintaining backward compatibility with much of the core configuration model.

nrpe(8), check_nrpe(1), service(8), systemctl(1)