How to Fix "Address Already in Use" Errors

This error occurs when a port is already occupied by another process.

Find What's Using the Port

ss -tulnp | grep :80
lsof -i :80

Solutions

1. Stop the conflicting service:

   systemctl stop apache2  # If Nginx needs port 80

2. Kill the process:

   kill $(lsof -t -i :80)

3. Change the port: Configure your application to use a different port