Common Pitfalls

The MAX_FILE_SIZE item cannot specify a file size greater than the file size that has been set in the upload_max_filesize in the php.ini file. The default is 2 megabytes.

If a memory limit is enabled, a larger memory_limit may be needed. Make sure you set memory_limit large enough.

If max_execution_time is set too small, script execution may be exceeded by the value. Make sure you set max_execution_time large enough.

Note: max_execution_time only affects the execution time of the script itself. Any time spent on activity that happens outside the execution of the script such as system calls using system(), the sleep() function, database queries, time taken by the file upload process, etc. is not included when determining the maximum time that the script has been running.

If post_max_size is set too small, large files cannot be uploaded. Make sure you set post_max_size large enough.

The max_file_uploads configuration setting controls the maximum number of files that can uploaded in one request. If more files are uploaded than the limit, then $_FILES will stop processing files once the limit is reached. For example, if max_file_uploads is set to 10, then $_FILES will never contain more than 10 items.

Not validating which file you operate on may mean that users can access sensitive information in other directories.

Due to the large amount of directory listing styles we cannot guarantee that files with exotic names (like containing spaces) are handled properly.

A developer may not mix normal input fields and file upload fields in the same form variable (by using an input name like foo[]).