Session files are usually stored in, say, /tmp/ on the server, and named sess_{session_id}. I have been looking at the contents and cannot figure out how they really work.
Fetching the variable name and and content from the file is easy. But how does PHP know what session belongs to whom?
The session_id seems totally random and one IP address can have several users, and each user can have several sessions if they have more than one browser window open.
So how does it work?