Nagios Installation Guide

Trademark Notice

Nagios® and the Nagios logo are trademarks of Nagios Enterprises, LLC. All trademarks and logos are used for representation purposes only. No prior copyright or trademark authorization has been obtained. This content is for educational purposes only.

Nagios is a powerful open-source monitoring system that enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes.

Installation Methods

Linux Installation (Ubuntu/Debian)

Install Nagios Core from Source

# Install prerequisites
sudo apt-get update
sudo apt-get install -y autoconf gcc libc6 make wget unzip apache2 php libapache2-mod-php7.4 libgd-dev

# Install Nagios Core build dependencies
sudo apt-get install -y libmcrypt-dev make libssl-dev bc gawk dc build-essential snmp libnet-snmp-perl gettext

# Download Nagios Core
cd /tmp
wget -O nagioscore.tar.gz https://github.com/NagiosEnterprises/nagioscore/archive/nagios-4.4.14.tar.gz
tar xzf nagioscore.tar.gz

# Compile Nagios Core
cd /tmp/nagioscore-nagios-4.4.14/
sudo ./configure --with-httpd-conf=/etc/apache2/sites-enabled
sudo make all

# Create user and group
sudo make install-groups-users
sudo usermod -a -G nagios www-data

# Install binaries and files
sudo make install
sudo make install-daemoninit
sudo make install-commandmode
sudo make install-config
sudo make install-webconf

# Enable Apache modules
sudo a2enmod rewrite
sudo a2enmod cgi

# Set up Nagios admin user
sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

# Start services
sudo systemctl restart apache2
sudo systemctl start nagios
sudo systemctl enable nagios

Install Nagios via Package Manager (Ubuntu)

# Add repository
sudo add-apt-repository ppa:nagios/nagios
sudo apt-get update

# Install Nagios
sudo apt-get install -y nagios4 nagios-plugins-contrib nagios-nrpe-plugin

# Start service
sudo systemctl start nagios4
sudo systemctl enable nagios4

Install on RHEL/CentOS

# Install EPEL repository
sudo yum install -y epel-release

# Install dependencies
sudo yum install -y gcc glibc glibc-common wget unzip httpd php gd gd-devel perl postfix

# Download and compile (similar to Ubuntu process above)
cd /tmp
wget https://github.com/NagiosEnterprises/nagioscore/archive/nagios-4.4.14.tar.gz
tar xzf nagios-4.4.14.tar.gz
cd nagioscore-nagios-4.4.14/

sudo ./configure
sudo make all
sudo make install-groups-users
sudo usermod -a -G nagios apache
sudo make install
sudo make install-init
sudo make install-commandmode
sudo make install-config
sudo make install-webconf

# Set SELinux permissions
sudo chcon -R -t httpd_sys_content_t /usr/local/nagios/share/
sudo chcon -R -t httpd_sys_rw_content_t /usr/local/nagios/var/

# Start services
sudo systemctl start nagios
sudo systemctl enable nagios
sudo systemctl restart httpd

Docker Installation

# Pull Nagios Docker image
docker pull jasonrivers/nagios:latest

# Run Nagios container
docker run -d --name nagios4 \
  -p 8080:80 \
  -v /path/to/nagios/etc:/opt/nagios/etc \
  -v /path/to/nagios/var:/opt/nagios/var \
  -v /path/to/custom-plugins:/opt/Custom-Nagios-Plugins \
  -e NAGIOSADMIN_USER=nagiosadmin \
  -e NAGIOSADMIN_PASS=nagiospassword \
  jasonrivers/nagios:latest

# Access at http://localhost:8080/nagios

Windows Installation (Using NSClient++)

# Download NSClient++ (Nagios agent for Windows)
# Visit https://nsclient.org/download/ and download the latest version

# Install NSClient++ silently
msiexec /i NSCP-0.5.2.35-x64.msi /quiet

# Configure NSClient++ for Nagios server
# Edit C:\Program Files\NSClient++\nsclient.ini

# Start NSClient++ service
Start-Service nscp

# Set to start automatically
Set-Service -Name nscp -StartupType Automatic

Install Nagios Plugins

# Download Nagios Plugins
cd /tmp
wget https://github.com/nagios-plugins/nagios-plugins/archive/release-2.4.6.tar.gz
tar xzf release-2.4.6.tar.gz
cd nagios-plugins-release-2.4.6/

# Compile and install
sudo ./tools/setup
sudo ./configure
sudo make
sudo make install

Configuration

Main Configuration File

Edit /usr/local/nagios/etc/nagios.cfg:

# Main Nagios configuration
log_file=/usr/local/nagios/var/nagios.log
cfg_dir=/usr/local/nagios/etc/objects
cfg_dir=/usr/local/nagios/etc/servers
object_cache_file=/usr/local/nagios/var/objects.cache
precached_object_file=/usr/local/nagios/var/objects.precache
resource_file=/usr/local/nagios/etc/resource.cfg
status_file=/usr/local/nagios/var/status.dat
status_update_interval=10
nagios_user=nagios
nagios_group=nagios
check_external_commands=1
command_file=/usr/local/nagios/var/rw/nagios.cmd

Define Hosts

Create /usr/local/nagios/etc/objects/myhost.cfg:

define host {
    use                     linux-server
    host_name               webserver1
    alias                   Production Web Server
    address                 192.168.1.100
    max_check_attempts      5
    check_period            24x7
    notification_interval   30
    notification_period     24x7
}

define service {
    use                     generic-service
    host_name               webserver1
    service_description     HTTP
    check_command           check_http
    notifications_enabled   1
}

define service {
    use                     generic-service
    host_name               webserver1
    service_description     SSH
    check_command           check_ssh
    notifications_enabled   1
}

Configure Notifications

Edit /usr/local/nagios/etc/objects/contacts.cfg:

define contact {
    contact_name                    admin
    alias                           Nagios Admin
    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                           admin@example.com
}

define contactgroup {
    contactgroup_name       admins
    alias                   Nagios Administrators
    members                 admin
}

NRPE Configuration (Remote Monitoring)

Install NRPE on monitored hosts:

# On Ubuntu/Debian
sudo apt-get install -y nagios-nrpe-server nagios-plugins

# Configure NRPE
sudo nano /etc/nagios/nrpe.cfg

NRPE configuration:

# Allow Nagios server IP
allowed_hosts=127.0.0.1,192.168.1.10

# Define commands
command[check_users]=/usr/lib/nagios/plugins/check_users -w 5 -c 10
command[check_load]=/usr/lib/nagios/plugins/check_load -w 15,10,5 -c 30,25,20
command[check_disk]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /
command[check_procs]=/usr/lib/nagios/plugins/check_procs -w 250 -c 400

Restart NRPE:

sudo systemctl restart nagios-nrpe-server

Verification

# Verify Nagios configuration
sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

# Check Nagios status
sudo systemctl status nagios

# Test plugin execution
/usr/local/nagios/libexec/check_http -H localhost

# Access Web Interface
# Navigate to: http://your-server-ip/nagios
# Login with nagiosadmin credentials

Advanced Configuration

Performance Data and Graphing (PNP4Nagios)

# Install PNP4Nagios for performance graphing
sudo apt-get install -y pnp4nagios

# Enable performance data processing
sudo nano /usr/local/nagios/etc/nagios.cfg

Add these lines:

process_performance_data=1
service_perfdata_command=process-service-perfdata
host_perfdata_command=process-host-perfdata

Monitoring MySQL

# Install MySQL plugin
sudo apt-get install -y nagios-plugins-mysql

# Create MySQL monitoring user
mysql -u root -p
CREATE USER 'nagios'@'localhost' IDENTIFIED BY 'password';
GRANT REPLICATION CLIENT ON *.* TO 'nagios'@'localhost';
FLUSH PRIVILEGES;

Define service:

define service {
    use                     generic-service
    host_name               dbserver
    service_description     MySQL
    check_command           check_mysql!nagios!password
}

API Monitoring

# Monitor REST APIs
/usr/local/nagios/libexec/check_http -H api.example.com \
  -u /api/health \
  -s "status\":\"healthy" \
  -w 2 -c 5

Troubleshooting

Common Issues

Nagios won't start:

# Check configuration
sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

# Check logs
sudo tail -f /usr/local/nagios/var/nagios.log

Web interface not accessible:

# Check Apache configuration
sudo apache2ctl configtest

# Restart Apache
sudo systemctl restart apache2

# Check permissions
sudo chown -R nagios:nagios /usr/local/nagios

Plugins not working:

# Verify plugin path
ls -la /usr/local/nagios/libexec/

# Test plugin manually
sudo -u nagios /usr/local/nagios/libexec/check_ping -H 8.8.8.8 -w 100,20% -c 500,60%

Best Practices

1. Organize Configuration Files: Use separate directories for different host groups
2. Set Realistic Thresholds: Avoid alert fatigue with appropriate warning/critical levels
3. Use Templates: Create host and service templates for consistency
4. Enable Notifications: Configure email, SMS, or Slack notifications
5. Monitor Nagios Itself: Set up self-monitoring checks
6. Regular Backups: Backup /usr/local/nagios/etc/ directory
7. Performance Tuning: Adjust check intervals based on infrastructure size
8. Documentation: Maintain a runbook for common alerts
9. Security: Use HTTPS, restrict web interface access, keep plugins updated
10. Distributed Monitoring: Use NRPE for remote host monitoring

Integration with Modern Tools

Nagios + Grafana

# Use Nagios data in Grafana
# Install Grafana Nagios datasource plugin
grafana-cli plugins install ibm-apm-datasource

Nagios + PagerDuty

Configure PagerDuty integration in contacts.cfg:

define contact {
    contact_name                    pagerduty
    alias                           PagerDuty
    service_notification_commands   notify-service-by-pagerduty
    host_notification_commands      notify-host-by-pagerduty
}

Resources

• Official Documentation: https://www.nagios.org/documentation/
• Nagios Exchange: https://exchange.nagios.org/ (plugins and addons)
• Community Forums: https://support.nagios.com/forum/
• GitHub: https://github.com/NagiosEnterprises/nagioscore

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Note: Nagios provides robust monitoring capabilities but requires manual configuration. For more automated, cloud-native monitoring, consider complementing with tools like Prometheus or Datadog.