The PHP upload file size limit is to limit the file size uploaded to the server through the HTTP protocol, so as to prevent uploading too large files from occupying server resources or causing the server to crash. In PHP, upload file size limit can be set through the following two configuration items:
- upload_max_filesize: Limit the maximum size of a single uploaded file.
- post_max_size: Limit the maximum size of the entire HTTP request, including uploaded files and other POST data.
These limits can be set in the php.ini configuration file, for example:
upload_max_filesize = 10M
post_max_size = 20M
The above configuration limits the uploaded file size to a maximum of 10MB, and the maximum size of the entire HTTP request to 20MB.
The underlying principle is that when a file is uploaded, PHP will temporarily store the content of the file in a temporary file, and then move the temporary file to the target location. Before moving the file, PHP checks whether the size of the file exceeds the upload file size limit. If the file size exceeds the limit, PHP will refuse to upload and return an error message. The post_max_size option that limits the maximum size of the entire HTTP request can also prevent users from attacking the server by sending large amounts of data through the POST method.
It is important to note that the upload file size limit is a fundamental security feature of PHP. The administrator should set appropriate limits according to the actual situation and usage requirements of the server. At the same time, the upload file size limit is only a simple control method, and cannot fully guarantee the security of the server, so other security measures are required to protect the server.