The file will probably be corrupt. To solve such issues one option is to make a copy of a file to be downloaded in a safe and atomic manner, then download the copy. For example you might run a cron job to do the copy using flock locally on the server. Copying takes a finite quantum of time so you would typically use a rename strategy to make a file 'appear' in a given dir in an atomic fashion and avoid the race condition which occurs while you are writing the copy.