Overview

After installing Cloudmon, accessing the application URL may display the default “Welcome to nginx” page instead of the Cloudmon UI.
You may also encounter the error below while reloading NGINX:

nginx: [emerg] duplicate default server for 0.0.0.0:80

This article explains why this happens and how to resolve it.

Symptoms

• Cloudmon installation is completed

• NGINX service is running

• Accessing the server IP/URL shows “Welcome to nginx”

• NGINX reload fails with a duplicate default server error

Root Cause

• NGINX is serving its default site instead of Cloudmon

• Multiple NGINX server blocks are configured with:

  listen 80 default_server;
  

• NGINX allows only one default server per IP and port

Step 1: Verify NGINX Is Listening on Port 80

ss -tulnp | grep :80

Expected:

• NGINX listening on 0.0.0.0:80 and [::]:80

• Multiple PIDs indicate worker processes, not multiple NGINX instances

Step 2: Check Enabled NGINX Sites

ls -l /etc/nginx/sites-enabled/

If the default site is enabled, NGINX will show the welcome page.

Step 3: Check for Duplicate Default Server Configuration

If you encounter:

nginx: [emerg] duplicate default server for 0.0.0.0:80

This indicates more than one server block is marked as default_server.

Step 4: Resolve the Duplicate Default Server Error

Choose one of the following options:

Option A (Recommended)

Disable the default site:

sudo rm /etc/nginx/sites-enabled/default

Option B

Edit the conflicting file and remove default_server:

listen 80;

Ensure only one server block (or none) uses default_server.

Step 5: Test and Reload NGINX

sudo nginx -t
sudo systemctl reload nginx

Expected output:

syntax is ok
test is successful

Verification

curl http://localhost

The NGINX welcome page should no longer appear, and Cloudmon should load once correctly mapped.