The Root Cause

Nginx Fatal Errors on AWS EC2 typically arise from permission conflicts or misconfigurations of the user directive within nginx.conf. This prevents Nginx from accessing critical log, cache, or configuration files, or from binding to its intended listening ports (e.g., 80/443).

Quick Fix (CLI)

1. Check Nginx configuration syntax: This often reveals immediate issues.

   sudo nginx -t

2. Review Nginx specific error logs: If syntax is okay, examine logs for detailed failure reasons.

   sudo tail -f /var/log/nginx/error.log
   # Alternatively, for systemd-based systems:
   # sudo journalctl -u nginx --since "1 hour ago"

3. Correct permissions for Nginx’s working directories: If logs indicate permission issues, ensure the Nginx user (e.g., nginx or www-data) owns essential directories. Adjust nginx:nginx if your user/group differs.

   sudo chown -R nginx:nginx /var/cache/nginx
   sudo chown -R nginx:nginx /var/lib/nginx
   sudo chown -R nginx:nginx /var/log/nginx

4. Restart the Nginx service:

   sudo systemctl restart nginx

Configuration Check

• File: /etc/nginx/nginx.conf
• Lines to change:
  1. Verify the user directive: This is typically at the top of the file. Ensure the specified user (e.g., nginx, www-data) exists on the system and has appropriate permissions to Nginx’s working directories. Adjust the user if it’s incorrect for your EC2 instance’s OS (e.g., nginx for Amazon Linux/CentOS, www-data for Ubuntu/Debian).

     user nginx; # Example: change 'nginx' to 'www-data' if applicable for your system

  2. Correct syntax errors: If sudo nginx -t reported a specific syntax error, navigate to the indicated file and line number (it might be an included file like /etc/nginx/conf.d/my-site.conf or within sites-enabled) and resolve the syntax issue.

Verification

1. Confirm Nginx configuration syntax is valid:

   sudo nginx -t

2. Restart Nginx to apply any configuration changes:

   sudo systemctl restart nginx

3. Check the Nginx service status to ensure it is running without errors:

   sudo systemctl status nginx

4. Verify Nginx is listening on the expected ports (e.g., 80 and 443):

   sudo ss -tulpn | grep nginx