nagios Linux: Complete Infrastructure Monitoring System Setup Guide

Introduction to Nagios

Nagios is one of the most popular open-source infrastructure monitoring systems available for Linux environments. Originally developed by Ethan Galstad in 1999, Nagios has evolved into a comprehensive monitoring solution that helps system administrators keep track of network services, host resources, and infrastructure components in real-time.

The name “Nagios” originally stood for “Nagios Ain’t Gonna Insist On Sainthood,” a recursive acronym that reflects the practical, no-nonsense approach of this monitoring tool. Today, Nagios serves as the backbone for monitoring critical infrastructure in organizations ranging from small businesses to large enterprises.

Key Features of Nagios

Nagios offers a comprehensive set of features that make it an excellent choice for infrastructure monitoring:

• Network Service Monitoring: Monitor HTTP, HTTPS, SMTP, POP3, NNTP, ICMP, SNMP, FTP, SSH, and other network protocols
• Host Resource Monitoring: Track processor load, disk usage, memory utilization, and running processes
• Simple Plugin Design: Allows users to easily develop custom service checks
• Parallelized Service Checks: Efficient monitoring through parallel execution
• Escalation and Notification System: Flexible alert mechanisms with multiple notification methods
• Web Interface: User-friendly web-based dashboard for monitoring and administration
• Optional Redundancy: Failover monitoring for critical systems

System Requirements

Before installing Nagios on your Linux system, ensure you meet the following requirements:

Hardware Requirements

• Minimum 2GB RAM (4GB recommended for larger environments)
• At least 20GB available disk space
• Multi-core processor (dual-core minimum)

Software Requirements

• Linux distribution (CentOS, RHEL, Ubuntu, Debian)
• Apache HTTP Server
• PHP (version 7.0 or later)
• GCC compiler
• GD library for image creation

Installing Nagios on Linux

Ubuntu/Debian Installation

First, update your system and install the required dependencies:

sudo apt update
sudo apt upgrade -y
sudo apt install -y apache2 php libapache2-mod-php php-gd libgd-dev
sudo apt install -y build-essential unzip wget openssl libssl-dev

Create a nagios user and group:

sudo useradd nagios
sudo groupadd nagcmd
sudo usermod -a -G nagcmd nagios
sudo usermod -a -G nagcmd www-data

Download and compile Nagios Core:

cd /tmp
wget https://github.com/NagiosEnterprises/nagioscore/archive/nagios-4.4.7.tar.gz
tar xzf nagios-4.4.7.tar.gz
cd nagioscore-nagios-4.4.7/
sudo ./configure --with-command-group=nagcmd
sudo make all
sudo make install
sudo make install-commandmode
sudo make install-init
sudo make install-config
sudo make install-webconf

CentOS/RHEL Installation

Install EPEL repository and required packages:

sudo yum install -y epel-release
sudo yum install -y httpd php gcc glibc glibc-common wget unzip
sudo yum install -y gd gd-devel make net-snmp openssl-devel xinetd

Create nagios user and group:

sudo useradd nagios
sudo groupadd nagcmd
sudo usermod -a -G nagcmd nagios
sudo usermod -a -G nagcmd apache

Follow the same compilation steps as Ubuntu, then start and enable services:

sudo systemctl start httpd
sudo systemctl enable httpd
sudo systemctl start nagios
sudo systemctl enable nagios

Installing Nagios Plugins

Nagios plugins are essential for monitoring various services and systems. Install the official plugin package:

cd /tmp
wget https://github.com/nagios-plugins/nagios-plugins/archive/release-2.3.3.tar.gz
tar xzf release-2.3.3.tar.gz
cd nagios-plugins-release-2.3.3/
sudo ./tools/setup
sudo ./configure
sudo make
sudo make install

Basic Nagios Configuration

Main Configuration File

The primary configuration file is located at /usr/local/nagios/etc/nagios.cfg. Key configuration parameters include:

# Main configuration file location
cfg_file=/usr/local/nagios/etc/objects/commands.cfg
cfg_file=/usr/local/nagios/etc/objects/contacts.cfg
cfg_file=/usr/local/nagios/etc/objects/timeperiods.cfg
cfg_file=/usr/local/nagios/etc/objects/templates.cfg

# Object configuration files
cfg_file=/usr/local/nagios/etc/objects/localhost.cfg

# Status file location
status_file=/usr/local/nagios/var/status.dat

# Command check interval
command_check_interval=-1

# Log file location
log_file=/usr/local/nagios/var/nagios.log

Web Interface Authentication

Create a web authentication user for the Nagios interface:

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

You’ll be prompted to enter a password for the nagiosadmin user.

Configuring Host Monitoring

Adding a New Host

Create a new configuration file for your hosts in /usr/local/nagios/etc/objects/:

sudo nano /usr/local/nagios/etc/objects/servers.cfg

Add a host definition:

define host{
    use                     linux-server
    host_name              web-server-01
    alias                  Web Server 01
    address                192.168.1.100
    max_check_attempts     5
    check_period           24x7
    notification_interval  30
    notification_period    24x7
}

Host Groups Configuration

Organize hosts into logical groups:

define hostgroup{
    hostgroup_name  web-servers
    alias           Web Servers
    members         web-server-01,web-server-02
}

Service Monitoring Configuration

Basic Service Checks

Configure service monitoring for your hosts:

define service{
    use                     generic-service
    host_name              web-server-01
    service_description    HTTP
    check_command          check_http
    max_check_attempts     4
    normal_check_interval  5
    retry_check_interval   1
}

Custom Service Checks

Create custom service definitions for specific monitoring needs:

define service{
    use                     generic-service
    host_name              web-server-01
    service_description    MySQL Database
    check_command          check_mysql
    max_check_attempts     3
    normal_check_interval  10
    retry_check_interval   2
}

Notification Configuration

Contact Definitions

Configure contacts for receiving notifications:

define contact{
    contact_name                    admin
    alias                          System Administrator
    service_notification_period    24x7
    host_notification_period       24x7
    service_notification_options   w,u,c,r
    host_notification_options      d,u,r
    service_notification_commands  notify-service-by-email
    host_notification_commands     notify-host-by-email
    email                          [email protected]
}

Contact Groups

Create contact groups for organized notification management:

define contactgroup{
    contactgroup_name   admins
    alias               Nagios Administrators
    members             admin,backup-admin
}

Advanced Monitoring Examples

Disk Usage Monitoring

Monitor disk usage on remote hosts using NRPE:

define service{
    use                     generic-service
    host_name              web-server-01
    service_description    Root Partition
    check_command          check_nrpe!check_disk
    max_check_attempts     4
    normal_check_interval  5
}

Load Average Monitoring

Monitor system load average:

define service{
    use                     generic-service
    host_name              web-server-01
    service_description    Current Load
    check_command          check_nrpe!check_load
    max_check_attempts     4
    normal_check_interval  5
}

Memory Usage Monitoring

Track memory utilization:

define service{
    use                     generic-service
    host_name              web-server-01
    service_description    Memory Usage
    check_command          check_nrpe!check_mem
    max_check_attempts     4
    normal_check_interval  10
}

Command Definitions

Commands define how Nagios executes checks. Common command definitions include:

define command{
    command_name    check_http
    command_line    $USER1$/check_http -H $HOSTADDRESS$ $ARG1$
}

define command{
    command_name    check_ssh
    command_line    $USER1$/check_ssh $HOSTADDRESS$
}

define command{
    command_name    check_ping
    command_line    $USER1$/check_ping -H $HOSTADDRESS$ -w $ARG1$ -c $ARG2$ -p 5
}

NRPE Configuration

Installing NRPE

NRPE (Nagios Remote Plugin Executor) allows remote monitoring:

cd /tmp
wget https://github.com/NagiosEnterprises/nrpe/archive/nrpe-4.0.3.tar.gz
tar xzf nrpe-4.0.3.tar.gz
cd nrpe-nrpe-4.0.3/
sudo ./configure --enable-command-args
sudo make all
sudo make install
sudo make install-config
sudo make install-init

NRPE Configuration on Client

Configure NRPE on the client machine:

sudo nano /usr/local/nagios/etc/nrpe.cfg

Add allowed hosts and command definitions:

allowed_hosts=127.0.0.1,192.168.1.10
command[check_users]=/usr/local/nagios/libexec/check_users -w 5 -c 10
command[check_load]=/usr/local/nagios/libexec/check_load -w 15,10,5 -c 30,25,20
command[check_disk]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /

Web Interface Overview

Access the Nagios web interface through your browser at http://your-server-ip/nagios. The interface provides several key sections:

• Tactical Overview: Quick summary of system status
• Host Detail: Detailed information about monitored hosts
• Service Detail: Current status of all monitored services
• Host Groups: Organized view of host collections
• Service Groups: Grouped service monitoring
• Problems: Current issues requiring attention

Troubleshooting Common Issues

Configuration Verification

Always verify your configuration before restarting Nagios:

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

Expected output for valid configuration:

Nagios Core 4.4.7
Copyright (c) 2009-present Nagios Core Development Team and Community Contributors
License: GPL

Website: https://www.nagios.org
Reading configuration data...
   Read main config file /usr/local/nagios/etc/nagios.cfg
   Processing object config files...
   
Total Warnings: 0
Total Errors: 0

Things look okay - No serious problems were detected during the pre-flight check

Permission Issues

Fix common permission problems:

sudo chown -R nagios:nagios /usr/local/nagios/
sudo chmod -R 755 /usr/local/nagios/

Service Start Issues

Check Nagios service status and logs:

sudo systemctl status nagios
sudo tail -f /usr/local/nagios/var/nagios.log

Performance Optimization

Check Interval Tuning

Optimize check intervals based on criticality:

define service{
    use                     generic-service
    host_name              critical-server
    service_description    Critical Service
    check_command          check_http
    normal_check_interval  1    # Check every minute
    retry_check_interval   1    # Retry immediately
}

Parallel Processing

Configure parallel processing for better performance:

# In nagios.cfg
max_concurrent_checks=20
check_result_reaper_frequency=10

Security Best Practices

Web Interface Security

Secure the web interface with SSL and strong authentication:

# Enable SSL in Apache configuration
sudo a2enmod ssl
sudo a2ensite default-ssl

File Permissions

Ensure proper file permissions for security:

sudo chmod 600 /usr/local/nagios/etc/htpasswd.users
sudo chown nagios:nagcmd /usr/local/nagios/var/rw/nagios.cmd

Backup and Recovery

Configuration Backup

Create regular backups of your Nagios configuration:

#!/bin/bash
BACKUP_DIR="/backup/nagios"
DATE=$(date +%Y%m%d_%H%M%S)
mkdir -p $BACKUP_DIR
tar -czf $BACKUP_DIR/nagios-config-$DATE.tar.gz /usr/local/nagios/etc/

Database Backup

If using Nagios with a database backend, include database backups:

mysqldump -u nagios -p nagios > /backup/nagios/nagios-db-$(date +%Y%m%d).sql

Integration with Other Tools

Integration with Grafana

Nagios can be integrated with Grafana for enhanced visualization. Install the Nagios datasource plugin and configure connection parameters to display Nagios metrics in custom dashboards.

Log Integration

Configure log forwarding to centralized logging systems:

# Configure rsyslog to forward Nagios logs
echo "local0.*    @@logserver:514" >> /etc/rsyslog.conf

Conclusion

Nagios remains one of the most powerful and flexible monitoring solutions available for Linux environments. Its extensive plugin ecosystem, robust notification system, and comprehensive monitoring capabilities make it an excellent choice for organizations of all sizes.

The key to successful Nagios implementation lies in proper planning, configuration management, and regular maintenance. Start with basic monitoring of critical services and gradually expand your monitoring coverage as you become more familiar with the system.

Remember to regularly update your Nagios installation, review and optimize configurations, and maintain proper backup procedures to ensure continuous monitoring capability for your infrastructure.