How can file permissions and ownership affect file uploads in PHP?

File permissions and ownership can affect file uploads in PHP by restricting the ability of the PHP script to write to the specified directory. To solve this issue, ensure that the directory where the files are being uploaded has the correct permissions set to allow the PHP script to write to it. Additionally, make sure that the ownership of the directory is set to the user running the PHP script.

// Set the correct permissions for the upload directory
chmod('upload_directory', 0777);

// Set the correct ownership for the upload directory
chown('upload_directory', 'www-data');