Solving the Fatal Error: Require_Once() Failed Opening Required - A Comprehensive Guide

In this comprehensive guide, we will discuss how to solve the fatal error: require_once() failed opening required. This error is commonly encountered by PHP developers and can be frustrating to deal with. Following our step-by-step guide, you will be able to resolve this error quickly and efficiently.

Table of Contents

  1. Understanding the Error
  2. Common Causes of the Error
  3. Step-by-Step Solution
  4. FAQs
  5. Related Links

Understanding the Error

The require_once() function is used to include a PHP file in another PHP file. It ensures that the included file is only included once during the execution of the script. If the file cannot be found or opened, the require_once() function will trigger a fatal error and halt the execution of the script.

The error message might look something like this:

Fatal error: require_once(): Failed opening required 'path/to/your/file.php' (include_path='.:/usr/local/php/pear') in /home/user/public_html/index.php on line 10

In this guide, we will focus on resolving the "Failed opening required" part of the error message.

Back to top ↑

Common Causes of the Error

The "Failed opening required" error is usually caused by one of the following reasons:

  1. The file path specified in the require_once() function is incorrect.
  2. The file you are trying to include does not exist or has been deleted.
  3. The file permissions are incorrect, preventing the file from being accessed.
  4. The PHP include_path configuration is incorrect.

Back to top ↑

Step-by-Step Solution

Follow these steps to resolve the "Failed opening required" error:

Step 1: Verify the File Path

First, check if the file path specified in the require_once() function is correct. Ensure that you are using the right path, either absolute or relative, to the file you want to include.

For example, if your file structure looks like this:

- public_html/
    - index.php
    - includes/
        - config.php

Your require_once() function in the index.php file should look like this:


Step 2: Check if the File Exists

Make sure the file you are trying to include actually exists. Double-check the file's location and verify that it has not been accidentally deleted or moved.

Step 3: Verify File Permissions

Check the file permissions of the file you are trying to include. The file should have read access for the user running the PHP script. You can change the file permissions using an FTP client or a command-line interface.

For example, to set the correct file permissions using the command line, navigate to the directory containing the file and run the following command:

chmod 644 config.php

Step 4: Check PHP include_path

If you have checked the file path, verified that the file exists, and ensured that the file has the correct permissions, but you are still encountering the error, the issue might be with the PHP include_path configuration.

You can check the current include_path by creating a new PHP file with the following content:


Run the script and look for the include_path entry in the "PHP Core" section. If the include_path is incorrect, you can change it in your php.ini file or by using the set_include_path() function in your PHP script.

After following these steps, the "Failed opening required" error should be resolved.

Back to top ↑


1. What is the difference between require_once() and include_once()?

The main difference between require_once() and include_once() is the behavior when the specified file cannot be found or opened. require_once() triggers a fatal error and halts the script execution, while include_once() triggers a warning and continues to execute the script.

2. When should I use require_once() instead of include() or require()?

You should use require_once() when you want to include a file that contains important functions or configurations that your script relies on, and you want to ensure that the file is only included once during the script execution.

3. Can I use a URL in the require_once() function?

No, you cannot use a URL in the require_once() function. It only works with local file paths.

4. What are the security risks of using require_once()?

The security risks of using require_once() are minimal if you use it to include your own files. However, if user input is used to determine the file to include, it can lead to a security vulnerability called "Local File Inclusion (LFI)." Always validate and sanitize user input before using it in your require_once() function.

5. How can I debug require_once() issues?

To debug require_once() issues, you can use the following techniques:

  1. Use the file_exists() function to check if the file exists before including it.
  2. Use the is_readable() function to check if the file is readable before including it.
  3. Use the error_reporting() function to enable error reporting and display errors.

Back to top ↑

  1. PHP: require_once - Manual
  2. PHP: include_once - Manual
  3. Understanding PHP File Permissions and Ownership
  4. PHP: set_include_path - Manual
  5. PHP: Local File Inclusion (LFI) - OWASP

Back to top ↑

Great! You’ve successfully signed up.

Welcome back! You've successfully signed in.

You've successfully subscribed to

Success! Check your email for magic link to sign-in.

Success! Your billing info has been updated.

Your billing was not updated.