Nagios Core on Ubuntu 24.04 on Azure User Guide

Overview

Nagios Core is the open-source industry standard for IT infrastructure monitoring — hosts, services, switches, applications and more — with alerting and a web dashboard. This cloudimg image installs Nagios Core 4 with its CGI web UI behind Apache, secured with Basic authentication, and generates a unique admin password on the first boot of every VM. Backed by 24/7 cloudimg support.

What is included:

• Nagios Core 4 with the standard monitoring plugins
• The Nagios CGI web UI served by Apache on port 80, secured with Basic auth for user nagiosadmin
• A per-VM nagiosadmin password generated at first boot, in a root-only file
• nagios4.service + apache2.service as systemd units, enabled and active
• 24/7 cloudimg support

Prerequisites

An active Azure subscription, an SSH key pair, and a VNet + subnet in the target region. Standard_B2s is a good starting point; scale up for monitoring many hosts. NSG inbound: allow 22/tcp from your management network and 80/tcp from the networks that need the Nagios UI (front port 80 with TLS for public exposure — see Enabling HTTPS).

Step 1 — Deploy from the Azure Marketplace

Sign in to the Azure Portal, choose Create a resource, search the Marketplace for Nagios Core by cloudimg, and select Create. On Basics pick your subscription, resource group, region and size; under Administrator account choose SSH public key and paste your key; under Inbound port rules allow SSH (22) and HTTP (80). Then Review + create → Create.

Step 2 — Deploy from the Azure CLI

az vm create \
  --resource-group <your-rg> \
  --name nagios \
  --image <marketplace-image-urn> \
  --size Standard_B2s \
  --admin-username azureuser \
  --ssh-key-values ~/.ssh/id_ed25519.pub \
  --vnet-name <your-vnet> --subnet <your-subnet> \
  --public-ip-sku Standard

az vm open-port --resource-group <your-rg> --name nagios --port 80 --priority 1010

Step 3 — Connect to your VM

ssh azureuser@<vm-public-ip>

Step 4 — Confirm the services are running

systemctl is-active nagios4.service apache2.service
curl -s -o /dev/null -w '%{http_code}\n' http://127.0.0.1/health.txt

Both services report active, and the unauthenticated health endpoint returns 200.

Step 5 — Retrieve your admin password

The password is generated uniquely on the first boot of your VM and written to a root-only file:

sudo cat /root/nagios-credentials.txt

The username is nagiosadmin; the password is the NAGIOS_ADMIN_PASSWORD value.

Step 6 — Sign in to the web UI

Browse to http://<vm-public-ip>/nagios4/ and sign in with nagiosadmin and the password from Step 5. You can confirm the authenticated endpoint from the shell — without credentials it returns 401, with them 200:

PW=$(sudo grep '^NAGIOS_ADMIN_PASSWORD=' /root/nagios-credentials.txt | cut -d= -f2-)
echo "unauthenticated: $(curl -s -o /dev/null -w '%{http_code}' http://127.0.0.1/nagios4/)"
echo "authenticated:   $(curl -s -o /dev/null -w '%{http_code}' -u "nagiosadmin:$PW" http://127.0.0.1/nagios4/)"

Step 7 — Add hosts and services

Nagios object definitions live in /etc/nagios4/. Add host and service definitions under /etc/nagios4/conf.d/ (or the configured cfg_dir), then verify and reload:

sudo /usr/sbin/nagios4 -v /etc/nagios4/nagios.cfg
sudo systemctl reload nagios4

The config check must report Things look okay before you reload.

Step 8 — Confirm the runtime

/usr/sbin/nagios4 --version | head -2

Enabling HTTPS

For production, terminate TLS at Apache with a real domain pointed at the VM's public IP. Install certbot and request a certificate (replace the domain):

sudo apt-get update && sudo apt-get install -y certbot python3-certbot-apache
sudo certbot --apache -d your-domain.example.com

Backup and maintenance

Your Nagios configuration lives in /etc/nagios4/. Keep the OS patched with sudo apt update && sudo apt upgrade, validate config changes with nagios4 -v before reloading, and back up /etc/nagios4/. The service restarts cleanly with sudo systemctl restart nagios4.

Support

This image is backed by 24/7 cloudimg support. Contact us by email and chat for help with host and service configuration, notifications, plugins, scaling and TLS.

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