How to Install Nagios on AlmaLinux 9

Nagios Core on AlmaLinux 9 — Enterprise-Grade Monitoring with a Stable RHEL Foundation

Nagios Core is a widely trusted open-source monitoring solution that provides health checks, status tracking, and alerting for infrastructure components. It is ideal for setups where configuration transparency, plugin extensibility, and system-level control are required.

AlmaLinux 9, as a downstream rebuild of Red Hat Enterprise Linux 9, delivers the security, performance, and long-term support needed for deploying Nagios Core in production environments, whether on bare metal, virtual machines, or containers.

Why Use Nagios Core on AlmaLinux 9?

AlmaLinux 9 is tailored for enterprise workloads. It provides a consistent and secure platform with 10+ years of lifecycle support—perfect for long-term monitoring solutions like Nagios.

AlmaLinux 9 Feature	Benefit for Nagios Core
Kernel 5.14 LTS	Modern hardware support and I/O optimization
Systemd 250+	Efficient service management for Nagios and Apache
SELinux (enforcing)	Strong access control, especially for plugin security
dnf & modularity	Allows selection of compatible PHP/Apache versions
OpenSSL 3.x	Required for TLS-secured plugin and web UI connections

This makes AlmaLinux a particularly good fit for air-gapped, compliance-driven, or mission-critical environments.

Nagios Core System Components

Nagios Core consists of:

nagios daemon — The main scheduling and check-processing engine
Apache with CGI — Provides the web interface
Object Definitions — Static configuration files for hosts, services, templates
Nagios Plugins — Executable scripts/binaries for health checks
Notification Handlers — Scripts that trigger alerts via email, SMS, or APIs

These components align well with the package and service management structures provided by AlmaLinux and the RHEL ecosystem.

Advantages of Using Nagios Core on AlmaLinux 9

Predictable OS Environment
AlmaLinux provides RPM-based consistency, great for automation and long-term configuration management.
Systemd Integration
Nagios and Apache services are easily managed, monitored, and restarted using systemctl.
Security Hardening
SELinux policies can restrict plugin behavior. Custom rules ensure Nagios only interacts with explicitly permitted resources.
Enterprise-Grade PHP Support
Through Application Streams, you can pin compatible PHP versions (like PHP 8.1 or 8.2) for CGI UI support.
FirewallD Compatibility
Easily configure secure access to Nagios UI and remote monitoring ports.
Minimal Overhead
AlmaLinux is optimized for headless, non-GUI workloads—ideal for server-grade deployments with high uptime expectations.

Use Cases for Nagios Core on AlmaLinux 9

Infrastructure Monitoring in Data Centers
Remote Site Monitoring via VPN or SSH
PCI-DSS or HIPAA-Compliant Environments
Air-Gapped Monitoring Networks
Hybrid Infrastructure (VMs, Physical, Cloud Instances)

Nagios Core’s text-based configurations and plugin architecture make it highly adaptable to a range of environments with strict audit or change control requirements.

Security Considerations

Security Layer	Implementation Strategy on AlmaLinux 9
SELinux	Create custom policies for plugin execution and file access
HTTPS (TLS)	Use Apache with mod_ssl and OpenSSL 3.x for encrypted UI
FirewallD	Restrict access to ports (80/443 or 5666 for NRPE)
Systemd Hardening	Apply unit restrictions like `ProtectSystem=full`
User Management	Define Nagios UI access via Apache’s htpasswd authentication

Combined, these features enable Nagios to operate within secure enclaves or externally exposed hardened networks.

Plugin Ecosystem & Extensions

Nagios Core on AlmaLinux supports:

Standard Nagios Plugins (check_http, check_disk, check_load, etc.)
NRPE / NCPA for remote Linux/Windows monitoring
SNMP tools for network device integration
Webhook/SMS integration for modern alerting via custom scripts
Visualization tools like Grafana (via PNP4Nagios or InfluxDB exporters)

Scripts can be written in Bash, Python, Perl, or compiled languages and run directly as part of the monitoring schedule.

Comparison with Other Monitoring Tools on AlmaLinux 9

Feature/Need	Nagios Core	Zabbix	Icinga 2
Transparency	Full config file control	Web-based	Hybrid (text + web)
Plugins	Custom and reusable	Integrated	Compatible with Nagios
Web Interface	Basic CGI	Rich UI	Rich UI + API
Time Series Data	External tools needed	Built-in	Optional via DB
Ease of Scaling	Manual / with addons	Native agent support	Distributed support

Nagios Core is best when full control over monitoring definitions, schedules, and scripts is preferred.

Running Nagios Core on AlmaLinux 9 gives you:

A secure and stable RHEL-class Linux environment
Long lifecycle support through 2032
Fine-tuned plugin execution and system resource usage
Compatibility with enterprise security models (SELinux, SSL, firewalls)
A mature and extensible monitoring platform for complex infrastructure

This setup is ideal for sysadmins and infrastructure teams seeking deterministic behavior, low resource usage, and deep customization.

Step 1: Create a Shape.Host Instance

Go to https://shape.host and log in.

Click “Create”, then choose “Instance”.

Choose a server location closest to your users.

Select AlmaLinux 9 (64-bit) as the OS.

Choose a plan with at least 2 CPUs, 2 GB RAM, and 10 GB SSD.

Click “Create Instance”.

After creation, copy the IP address of the server.

Step 2: Connect to the Instance

On Linux/macOS:

ssh root@your-server-ip

On Windows:

Download and install PuTTY.
Open PuTTY and enter your server’s IP.
Log in as root when prompted.

Step 3: Update the system

dnf update -y

This ensures all packages are up to date.

Step 4: Install Required Packages

dnf install httpd php php-cli gcc glibc glibc-common unzip wget make autoconf automake libtool libxml2 libxml2-devel gd gd-devel openssl openssl-devel perl gettext -y

Installs Apache, PHP, compilers, libraries, and other dependencies needed for compiling and running Nagios.

Step 5: Create Nagios User and Group

useradd nagios

Creates the nagios user.

groupadd nagcmd

Creates the nagcmd group for command access.

usermod -a -G nagcmd nagios
usermod -a -G nagcmd apache

Adds nagios and apache users to nagcmd group.

Step 6: Download and Compile Nagios Core

cd /usr/src
wget -O nagioscore.tar.gz https://github.com/NagiosEnterprises/nagioscore/archive/refs/tags/nagios-4.5.9.tar.gz
tar xzf nagioscore.tar.gz
cd nagioscore-nagios-4.5.9

Downloads and extracts Nagios Core source code.

./configure --with-command-group=nagcmd
make all

Configures and compiles Nagios.

Step 7: Install Nagios

make install
make install-init
make install-commandmode
make install-config
make install-webconf

Installs Nagios binaries, daemon, command mode, configuration files, and web config for Apache.

Step 8: Create Web Login

htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

Creates the nagiosadmin login for accessing the Nagios web interface.

Step 9: Enable and Start Apache

systemctl enable httpd
systemctl start httpd
systemctl status httpd

Starts and enables the Apache web server.

Step 10: Install Nagios Plugins

cd /usr/src
wget -O nagios-plugins.tar.gz https://github.com/nagios-plugins/nagios-plugins/archive/refs/tags/release-2.4.12.tar.gz
tar xzf nagios-plugins.tar.gz
cd nagios-plugins-release-2.4.12

Downloads and extracts Nagios plugins.

./tools/setup
./configure --with-nagios-user=nagios --with-nagios-group=nagios
make
make install

Configures, compiles, and installs plugins.

Step 11: Verify Configuration and Start Nagios

/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

Checks if your Nagios config is valid.

systemctl enable nagios
systemctl start nagios
systemctl status nagios

Starts and enables Nagios monitoring.

Step 12: Access Nagios Web Interface

Open your browser and go to:

http://your-server-ip/nagios

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