short answer: none (except the file you're uploading). long answer: only the file you willingly upload will be stored on the disk of the server but information about your client will be logged only to the terminal, and will be lost upon a server restart. if this changes and i start to store these logs, or i keep file entries in a database again (which was the case at one point) then this page will be updated to state this.

what i see for an upload: