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Learn how to Deploy Nagios on Ubuntu VPS! This guide walks through deploying Nagios Core on an Ubuntu VPS, from system prep to web access, plugins, hosts/services, and hardening. Commands target Ubuntu 22.04 LTS (works similarly on 20.04/24.04). What You’ll Build A Nagios Core monitoring server Web UI secured with HTTP auth Standard monitoring plugins Example host & service checks Basic security and troubleshooting Prerequisites Ubuntu VPS with root or sudo access 2 vCPU / 2 GB RAM minimum (4 GB recommended) Public IP or hostname Open ports: 80/443 (web), 5666 (optional NRPE) How to Deploy Nagios on Ubuntu VPS (Step-by-Step) To deploy Nagios on Ubuntu VPS, follow the steps below: Update the System sudo apt update && sudo apt upgrade -y sudo reboot Install Required Packages Nagios Core is typically compiled from source for the latest stable features. sudo apt-get install -y autoconf gcc libc6 make wget unzip apache2 php libapache2-mod-php libgd-dev ufw sudo apt-get install -y openssl libssl-dev Enable Apache modules: sudo a2enmod rewrite cgi sudo systemctl restart apache2 Create Nagios User & Groups sudo useradd nagios sudo groupadd nagcmd sudo usermod -aG nagcmd nagios sudo usermod -aG nagcmd www-data Download & Compile Nagios Core cd /tmp wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.5.5.tar.gz tar xzf nagios-4.5.5.tar.gz cd nagios-4.5.5 Configure and build: ./configure --with-command-groupnagcmd make all sudo make install sudo make install-init sudo make install-commandmode sudo make install-config sudo make install-webconf Set Apache Authentication Create a web admin user: sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin Restart Apache: sudo systemctl restart apache2 Install Nagios Plugins Plugins power checks (CPU, disk, HTTP, ping, etc.). cd /tmp wget https://nagios-plugins.org/download/nagios-plugins-2.4.8.tar.gz tar xzf nagios-plugins-2.4.8.tar.gz cd nagios-plugins-2.4.8 ./configure --with-nagios-usernagios --with-nagios-groupnagios make sudo make install Start & Enable Nagios sudo systemctl enable nagios sudo systemctl start nagios Verify config before restarts: sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg Access the Web Interface Open in your browser: http://YOUR_SERVER_IP/nagios Login with: Username: nagiosadmin Password: (set earlier) Add a Host to Monitor Create a hosts file: sudo nano /usr/local/nagios/etc/objects/hosts.cfg Example: define host { use linux-server host_name web01 alias Web Server 01 address 192.0.2.10 max_check_attempts 5 check_period 24x7 notification_interval 30 notification_period 24x7 } Include it in nagios.cfg: sudo nano /usr/local/nagios/etc/nagios.cfg Add: cfg_file/usr/local/nagios/etc/objects/hosts.cfg Restart: sudo systemctl restart nagios Add Service Checks Edit services: sudo nano /usr/local/nagios/etc/objects/services.cfg Example HTTP check: define service { use generic-service host_name web01 service_description HTTP check_command check_http } Restart Nagios after changes. (Optional) Monitor Remote Servers with NRPE Install NRPE on the remote host: sudo apt install -y nagios-nrpe-server nagios-plugins Allow the Nagios server IP in: sudo nano /etc/nagios/nrpe.cfg Restart NRPE: sudo systemctl restart nagios-nrpe-server On the Nagios server, define NRPE commands and services. Secure & Harden Use HTTPS (Let’s Encrypt with Apache) Restrict /nagios via firewall/IP allowlist Change default object definitions Rotate logs (/usr/local/nagios/var/) Use ufw: sudo ufw allow OpenSSH sudo ufw allow 80 sudo ufw enable Troubleshooting Check status sudo systemctl status nagios Validate config sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg Common paths Config: /usr/local/nagios/etc/ Plugins: /usr/local/nagios/libexec/ Logs: /usr/local/nagios/var/nagios.log HTTPS + Let’s Encrypt Automation for Nagios on Ubuntu VPS Now that we know how to deploy Nagios on Ubuntu VPS, let's add HTTPS and Let's Encrypt automation. This guide secures the Nagios web interface with HTTPS using automated certificates from Let's Encrypt, via Certbot on Apache. It includes automatic renewal and validation checks. Assumptions Nagios Core already installed at /usr/local/nagios Apache in use (apache2) Public DNS name pointing to your VPS (recommended) Ubuntu 20.04 / 22.04 / 24.04 To configure HTTPS + Let's Encrypt automation for Nagios on Ubuntu VPS, follow the steps below: Install Certbot for Apache sudo apt update sudo apt install -y certbot python3-certbot-apache Verify: certbot --version Nagios installs its Apache config here: /etc/apache2/conf-enabled/nagios.conf Confirm Apache is serving on port 80: sudo apachectl -S You should see your Nagios site bound to *:80. Obtain the SSL Certificate (Auto-Configure Apache) Run Certbot and let it modify Apache automatically: sudo certbot --apache During prompts: Enter your email Agree to TOS Choose the domain serving Nagios (e.g. nagios.example.com) Select Redirect HTTP to HTTPS (recommended) Certbot will: Issue the certificate Create SSL VirtualHost Add redirect rules Verify HTTPS Access Open in browser: https://nagios.example.com/nagios Confirm: Valid certificate No mixed-content warnings Login works normally Force HTTPS for Nagios (Optional Hardening) If you want an explicit redirect at Apache level: sudo nano /etc/apache2/conf-enabled/nagios.conf Add near the top: RewriteEngine On RewriteCond %{HTTPS} !on RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} Reload Apache: sudo systemctl reload apache2 Automatic Certificate Renewal (Systemd Timer) Certbot installs a systemd timer by default. Check status: systemctl list-timers | grep certbot Test renewal safely: sudo certbot renew --dry-run No errors automation is working. Harden TLS Configuration (Recommended) Edit the SSL VirtualHost created by Certbot (usually): /etc/apache2/sites-enabled/000-default-le-ssl.conf Add: SSLProtocol all -SSLv3 -TLSv1 -TLSv1.1 SSLCipherSuite HIGH:!aNULL:!MD5 SSLHonorCipherOrder on Header always set Strict-Transport-Security "max-age63072000; includeSubDomains; preload" Enable headers module if needed: sudo a2enmod headers sudo systemctl reload apache2 Firewall Check Ensure HTTPS is allowed: sudo ufw allow 443 sudo ufw reload Common Issues & Fixes Certificate issued but browser still shows HTTP Apache reload required: sudo systemctl reload apache2 Certbot fails validation DNS not pointing to server Port 80 blocked by firewall Incorrect VirtualHost Mixed content warning Ensure no http:// references in custom Nagios UI assets File Locations (Quick Reference) Certificates: /etc/letsencrypt/live/nagios.example.com/ Apache SSL vhost: /etc/apache2/sites-enabled/*-le-ssl.conf Nagios Apache config: /etc/apache2/conf-enabled/nagios.conf Result You now have: Full HTTPS encryption Automatic 90-day certificate renewal Enforced HTTPS redirects Hardened TLS configuration Summary You now know how to deploy Nagios on Ubuntu VPS.

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