Why Does My File Upload Fail When `upload_max_filesize` is Set Higher Than `post_max_size`?

Understanding the Role of post_max_size and upload_max_filesize in PHP

When working with file uploads in PHP, it is crucial to understand the interplay between the post_max_size and upload_max_filesize directives. These settings determine the maximum allowable size for file uploads, but they serve distinct purposes.

Defining the Difference

• upload_max_filesize: This directive sets the maximum size limit for individual files being uploaded.
• post_max_size: This directive specifies the maximum size limit for the entire HTTP request body, including all form data and uploaded files.

Impact on File Uploads

In your scenario, despite setting upload_max_filesize to 16MB, you faced an error indicating that post_max_size (8MB) was exceeded. This is because post_max_size limits the overall size of the request body, which includes the content of the form and any uploaded files.

Clarifying the Limits

To clarify, upload_max_filesize acts as a cap on the size of each individual file that can be uploaded. Meanwhile, post_max_size imposes a limit on the cumulative size of all data that can be submitted in the request.

How to Send Larger Files

If you need to upload files larger than what post_max_size allows, you can't increase upload_max_size. Instead, you must adjust post_max_size to accommodate the larger file size.

Recognizing Exceeding post_max_size

It's worth noting that PHP doesn't provide a clear indication when post_max_size is exceeded. Typically, $_POST and $_FILES will be empty, but $_SERVER['CONTENT_LENGTH'] will be non-zero. By monitoring this combination, you can identify when post_max_size has been reached.

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