nagios

Start nagios

$ nagios /etc/nagios/nagios.cfg

$ nagios -d

$ nagios -s

$ nagios -v

nagios [-d] [-f config_file] [-p pid_file] [-u user] [-g group] [-l log_file] [-s status_file] [-v] [-t]

Note: Direct invocation of the nagios daemon with these options is less common. It is usually started, stopped, and reloaded via system service management commands (e.g., systemctl start nagios).

-d
    Run the nagios daemon in the background.

-f config_file
    Specify the main Nagios configuration file to use. This file typically points to other configuration files.

-p pid_file
    Specify the path to the PID file where the daemon's process ID will be stored.

-u user
    Run the nagios daemon as the specified user. This is important for security.

-g group
    Run the nagios daemon as the specified group.

-l log_file
    Specify the path to the event log file where Nagios will write its operational logs.

-s status_file
    Specify the path to the status file, which stores real-time monitoring information for the web interface.

-v
    Display the version information for the Nagios daemon and exit.

-t
    Test the specified configuration files for validity and exit. This is crucial for troubleshooting configuration issues.

The nagios command refers to the core daemon of the Nagios monitoring system. Nagios is a widely-used, open-source tool designed to monitor hosts, services, and network devices across an entire IT infrastructure. Its primary function is to continuously check the status of defined objects (like servers, routers, services such as HTTP, SSH, or disk space) by executing various monitoring plugins. If a check fails or deviates from predefined thresholds, Nagios can generate alerts and send notifications via various methods, including email, SMS, or custom scripts.

The daemon maintains a comprehensive view of the network's health, logs events, and provides a centralized web interface for administrators to view current status, historical data, and manage alerts. While nagios is the executable that runs the main monitoring process, it is typically managed and controlled through system service managers (like systemd or SysVinit scripts) rather than being directly invoked by users from the command line for daily operations.

The nagios daemon is primarily a background service and is rarely invoked directly by users with its command-line options. Its lifecycle (start, stop, reload) is almost exclusively managed by operating system service managers like systemd or traditional SysVinit scripts.

Nagios relies heavily on a complex set of external configuration files, and proper functionality requires careful and extensive setup. The actual monitoring tasks are performed by external Nagios plugins, which are separate executables that the daemon invokes.

The nagios daemon's behavior is entirely defined by a hierarchy of configuration files (e.g., nagios.cfg, commands.cfg, hosts.cfg, services.cfg, timeperiods.cfg, etc.). These files specify what to monitor, how often, who to notify, and more. A common practice is to organize these files into separate directories for clarity.

The core nagios daemon does not perform actual checks itself. Instead, it relies on external executables called Nagios Plugins. These are independent scripts or binaries (e.g., check_http, check_disk, check_cpu) that perform specific checks and return their status (OK, WARNING, CRITICAL, UNKNOWN) and performance data in a standardized format that Nagios understands. This plugin architecture makes Nagios highly extensible.

While nagios is a command-line daemon, its primary user interface for monitoring status, acknowledging problems, and viewing historical data is a comprehensive web interface. This interface provides dashboards, status maps, reports, and event logs, making it easy for administrators to get an overview of their monitored environment.

Nagios originated in 1999 as NetSaint, developed by Ethan Galstad. It was initially designed as a simple host and service monitoring application. Due to trademark issues, the project was renamed to Nagios (a recursive acronym for 'Nagios Ain't Gonna Insist On Sainthood') in 2002.

Over the years, Nagios has evolved significantly, becoming one of the most popular and influential open-source monitoring solutions. It has spawned a rich ecosystem of plugins, add-ons, and commercial derivatives like Nagios XI, while Nagios Core remains the free and open-source foundation.

systemctl(1), service(8), nagiostats(8), check_http(8), check_disk(8), check_ping(8)