Deploy Nagios Core on RamNode VPS

Why Nagios Core?

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

Monitor servers, networks, and applications

Flexible alerting and escalation policies

Extensible with thousands of plugins

Web-based dashboard interface

Prerequisites

Requirements

• Ubuntu 22.04 or Debian 12
• Root or sudo access
• Minimum 1 GB RAM
• 20 GB disk space

Optional

• Domain name for web access
• SSL certificate
• Mail server for notifications
• Additional hosts to monitor

Update Your System

Start by ensuring your system is up to date:

System Update

sudo apt update && sudo apt upgrade -y

Install Dependencies

Install Required Packages

Install Apache, PHP, and build tools:

Install Dependencies

sudo apt install -y apache2 php libapache2-mod-php php-gd \
    wget unzip curl openssl libssl-dev build-essential \
    libgd-dev libperl-dev daemon autoconf gcc make

Create Nagios User and Group

Create dedicated user and group for Nagios:

Create User

sudo useradd -m -s /bin/bash nagios
sudo groupadd nagcmd
sudo usermod -aG nagcmd nagios
sudo usermod -aG nagcmd www-data

Install Nagios Core

Download Nagios Core

Download the latest Nagios Core release:

Download Nagios

cd /tmp
NAGIOS_VER="4.5.2"
wget https://github.com/NagiosEnterprises/nagioscore/releases/download/nagios-${NAGIOS_VER}/nagios-${NAGIOS_VER}.tar.gz
tar -xzf nagios-${NAGIOS_VER}.tar.gz
cd nagios-${NAGIOS_VER}

Compile and Install

Compile and install Nagios:

Build Nagios

./configure --with-httpd-conf=/etc/apache2/sites-enabled \
    --with-command-group=nagcmd
make all
sudo make install
sudo make install-init
sudo make install-commandmode
sudo make install-config
sudo make install-webconf

Configure Apache

Enable required Apache modules and create admin user:

Apache Setup

# Enable required modules
sudo a2enmod rewrite cgi

# Create Nagios admin user for web interface
sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

# You'll be prompted to enter and confirm a password
# Save this password securely!

# Restart Apache
sudo systemctl restart apache2

Install Nagios Plugins

Download and Install Plugins

Install the official Nagios plugins:

Install Plugins

cd /tmp
PLUGINS_VER="2.4.10"
wget https://github.com/nagios-plugins/nagios-plugins/releases/download/release-${PLUGINS_VER}/nagios-plugins-${PLUGINS_VER}.tar.gz
tar -xzf nagios-plugins-${PLUGINS_VER}.tar.gz
cd nagios-plugins-${PLUGINS_VER}

# Compile and install
./configure --with-nagios-user=nagios --with-nagios-group=nagios
make
sudo make install

Install Memory Check Plugin

Install a custom memory monitoring plugin:

Memory Plugin

cd /usr/local/nagios/libexec
sudo wget -O check_mem https://raw.githubusercontent.com/justintime/nagios-plugins/master/check_mem/check_mem.pl
sudo chmod +x check_mem
sudo chown nagios:nagios check_mem

# Verify it works
/usr/local/nagios/libexec/check_mem -f -w 80 -c 90

Start Nagios

Verify configuration and start Nagios:

Start Nagios

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

# Enable and start Nagios service
sudo systemctl enable nagios
sudo systemctl start nagios

# Check status
sudo systemctl status nagios

Command Definitions

Define Check Commands

Edit the commands configuration:

Edit Commands

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

commands.cfg

# Memory check command
define command {
    command_name    check_local_mem
    command_line    $USER1$/check_mem -f -w $ARG1$ -c $ARG2$
}

# Disk check command
define command {
    command_name    check_local_disk
    command_line    $USER1$/check_disk -w $ARG1$ -c $ARG2$ -p $ARG3$
}

# Load check command
define command {
    command_name    check_local_load
    command_line    $USER1$/check_load -w $ARG1$ -c $ARG2$
}

Monitoring Configuration

Create VPS Configuration

Create a monitoring configuration for your VPS:

Create Config File

sudo nano /usr/local/nagios/etc/objects/ramnode-vps.cfg

ramnode-vps.cfg

# Host definition
define host {
    use                     linux-server
    host_name               ramnode-vps
    alias                   RamNode VPS Server
    address                 127.0.0.1
    max_check_attempts      5
    check_period            24x7
    notification_interval   30
    notification_period     24x7
}

# PING check
define service {
    use                     local-service
    host_name               ramnode-vps
    service_description     PING
    check_command           check_ping!100.0,20%!500.0,60%
}

# Root partition disk space
define service {
    use                     local-service
    host_name               ramnode-vps
    service_description     Disk Space - Root
    check_command           check_local_disk!20%!10%!/
}

# Memory usage
define service {
    use                     local-service
    host_name               ramnode-vps
    service_description     Memory Usage
    check_command           check_local_mem!80!90
}

# System load
define service {
    use                     local-service
    host_name               ramnode-vps
    service_description     System Load
    check_command           check_local_load!5.0,4.0,3.0!10.0,8.0,6.0
}

# Current users
define service {
    use                     local-service
    host_name               ramnode-vps
    service_description     Current Users
    check_command           check_local_users!20!50
}

# Total processes
define service {
    use                     local-service
    host_name               ramnode-vps
    service_description     Total Processes
    check_command           check_local_procs!250!400!RSZDT
}

# SSH service
define service {
    use                     local-service
    host_name               ramnode-vps
    service_description     SSH
    check_command           check_ssh
}

# HTTP service
define service {
    use                     local-service
    host_name               ramnode-vps
    service_description     HTTP
    check_command           check_http
}

# Swap usage
define service {
    use                     local-service
    host_name               ramnode-vps
    service_description     Swap Usage
    check_command           check_local_swap!20%!10%
}

Include Configuration

Add the new config to Nagios:

Edit nagios.cfg

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

# Add this line:
cfg_file=/usr/local/nagios/etc/objects/ramnode-vps.cfg

Validate and Restart

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

# Restart Nagios
sudo systemctl restart nagios

Threshold Tuning

Recommended Thresholds by VPS Size

VPS Size	Load Warning	Load Critical	Mem Warn	Mem Crit
1 vCPU	1.5,1.2,1.0	3.0,2.5,2.0	80	90
2 vCPU	3.0,2.5,2.0	6.0,5.0,4.0	80	90
4 vCPU	6.0,5.0,4.0	12.0,10.0,8.0	85	95
8 vCPU	12.0,10.0,8.0	24.0,20.0,16.0	85	95

Load values are: 1-minute, 5-minute, 15-minute averages.

Security

Enable HTTPS with Let's Encrypt

Secure your Nagios installation with SSL:

Install Certbot

sudo apt install -y certbot python3-certbot-apache
sudo certbot --apache -d nagios.yourdomain.com

Restrict Access by IP

Limit access to trusted IPs:

Edit Apache Config

sudo nano /etc/apache2/sites-enabled/nagios.conf

IP Restrictions

<Directory "/usr/local/nagios/sbin">
    Options ExecCGI
    AllowOverride None
    <RequireAll>
        Require all granted
        Require ip 192.168.1.0/24
        Require ip your.public.ip.address
    </RequireAll>
    AuthName "Nagios Access"
    AuthType Basic
    AuthUserFile /usr/local/nagios/etc/htpasswd.users
    Require valid-user
</Directory>

Restart Apache

sudo systemctl restart apache2

Configure Firewall

Open required ports:

UFW Rules

sudo ufw allow 80/tcp
sudo ufw allow 443/tcp
sudo ufw enable

Email Notifications

Install Mail Utilities

Install mail tools for notifications:

Install Mail

sudo apt install -y mailutils postfix

# During Postfix installation:
# - Select "Internet Site"
# - Enter your server's hostname

Configure Contacts

Update the Nagios admin contact:

Edit Contacts

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

contacts.cfg

define contact {
    contact_name    nagiosadmin
    use             generic-contact
    alias           Nagios Admin
    email           your-email@domain.com
}

Restart Nagios

sudo systemctl restart nagios

Testing

Verify Services

Check that all services are running:

Check Status

sudo systemctl status nagios
sudo systemctl status apache2

Test Plugins Manually

Test each plugin from the command line:

Plugin Tests

# Test disk check
/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /

# Test memory check
/usr/local/nagios/libexec/check_mem -f -w 80 -c 90

# Test load check
/usr/local/nagios/libexec/check_load -w 5.0,4.0,3.0 -c 10.0,8.0,6.0

# Test swap check
/usr/local/nagios/libexec/check_swap -w 20% -c 10%

Access Web Interface

Navigate to the Nagios dashboard:

Web URL

http://your-vps-ip/nagios

Troubleshooting

Common Issues

Nagios won't start

Debug

sudo journalctl -u nagios -f
sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

Permission denied errors

Fix Permissions

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

Web interface shows "Forbidden"

Enable CGI

sudo a2enmod cgi
sudo systemctl restart apache2

Plugins returning unknown status

Check Plugins

# Check plugin permissions
ls -la /usr/local/nagios/libexec/

# Test as nagios user
sudo -u nagios /usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /

Next Steps

→Configure NRPE for remote host monitoring

→Integrate with Slack or PagerDuty

→Add custom plugins from Nagios Exchange

→Set up event handlers for auto-remediation

Self-Hosted Nagios Core

Why Nagios Core?

Prerequisites

Requirements

Optional

Update Your System

Install Dependencies

Install Required Packages

Create Nagios User and Group

Install Nagios Core

Download Nagios Core

Compile and Install

Configure Apache

Install Nagios Plugins

Download and Install Plugins

Install Memory Check Plugin

Start Nagios

Command Definitions

Define Check Commands

Monitoring Configuration

Create VPS Configuration

Include Configuration

Threshold Tuning

Recommended Thresholds by VPS Size

Security

Enable HTTPS with Let's Encrypt

Restrict Access by IP

Configure Firewall

Email Notifications

Install Mail Utilities

Configure Contacts

Testing

Verify Services

Test Plugins Manually

Access Web Interface

Troubleshooting

Common Issues

Nagios won't start

Permission denied errors

Web interface shows "Forbidden"

Plugins returning unknown status

Next Steps