Top 5 Common Nginx Errors on Ubuntu and How to Fix Them

Nginx is a popular open-source web server known for its performance, stability, and flexibility. However, even with its robust nature, Nginx can encounter errors from time to time. These errors can range from minor configuration issues to more severe problems that can bring your website down.

In this guide, we’ll explore the top 5 common Nginx errors on Ubuntu and provide step-by-step instructions on how to identify and resolve them.

1. Syntax Errors

Syntax errors are the most common type of Nginx error and typically occur due to incorrect configuration directives or missing semicolons. These errors can prevent Nginx from starting or cause it to malfunction.

Identifying Syntax Errors:

• Check the Nginx error log for messages indicating syntax errors. The default error log location is usually /var/log/nginx/error.log.
• Use the nginx -t command to test the Nginx configuration file for syntax errors. This command will display any errors or warnings found in the configuration file.

Resolving Syntax Errors:

• Carefully review the error messages to identify the specific syntax error.
• Open the Nginx configuration file using a text editor and make the necessary corrections.
• Save the configuration file and reload Nginx using the sudo systemctl reload nginx command.

2. Permission Denied Errors

Permission denied errors arise when Nginx doesn’t have the necessary permissions to access files or directories. This can happen due to incorrect file ownership or group permissions.

Identifying Permission Denied Errors:

• Check the Nginx error log for messages indicating permission denied errors.
• Look for specific error messages like permission denied opening directory or no permission to read file.

Resolving Permission Denied Errors:

• Identify the file or directory that Nginx is trying to access.
• Check the ownership and group permissions of the file or directory using the ls -l command.
• Grant Nginx the necessary permissions using the chown or chgrp commands.
• Reload Nginx using the sudo systemctl reload nginx command.

3. 500 Internal Server Error

The 500 Internal Server Error is a generic error message that indicates an unexpected problem on the server’s side. This error can be caused by various factors, such as PHP errors, application errors, or misconfigured modules.

Identifying the Root Cause of 500 Errors:

• Check the Nginx error log for more detailed error messages.
• Enable PHP error logging to reveal specific PHP errors.
• Check the application logs for any relevant error messages.

Resolving 500 Errors:

• Troubleshoot the specific error message or exception reported in the logs.
• Fix any PHP errors or application errors that are causing the issue.
• Restart Nginx and the application server if necessary.

4. 404 Not Found Error

The 404 Not Found Error indicates that the requested resource (file, directory, or web page) could not be found on the server. This can happen due to incorrect URLs, missing files, or misconfigured server blocks.

Identifying the Cause of 404 Errors:

• Verify that the requested URL is correct and matches the actual file or directory structure.
• Check if the requested file or directory exists on the server.
• Review the Nginx server blocks to ensure they are configured correctly for the requested resources.

Resolving 404 Errors:

• Correct any typos or errors in the requested URL.
• Create the missing file or directory if it’s necessary.
• Update the Nginx server blocks to point to the correct file or directory locations.
• Reload Nginx using the sudo systemctl reload nginx command.

5. Upstream Connection Errors

Upstream connection errors occur when Nginx is unable to connect to backend servers, such as PHP-FPM or application servers. This can happen due to network issues, server downtime, or incorrect configuration settings.

Identifying Upstream Connection Errors:

• Check the Nginx error log for messages indicating upstream connection failures.
• Look for error messages like connect() failed errno=111 Connection refused or failed to connect to upstream server.

Resolving Upstream Connection Errors:

• Verify that the backend servers are running and accessible.
• Check the network connectivity between Nginx and the backend servers.
• Ensure the Nginx configuration is correct for upstream connections, including server names, ports, and timeouts.
• Reload Nginx using the sudo systemctl reload nginx command.

By following these steps and understanding the common causes of Nginx errors, you’ll be well-equipped to troubleshoot and resolve issues, ensuring your Nginx-powered website remains up and running smoothly.