I need a method of stopping concurrent logins using PHP/MySQL.

**The current setup**

Currently there are 2 people sharing the same login on a system i have built internally where i work. Due to the nature of the system i dont want them both logging in.

**What I have tried**

Around 10 articles on stackoverflow and googled for as long as i can.

I also attempted adding a "loggedin" field in the user table which upon logging in was set to 1 and upon logging out was set to 0. Then if the same user credentials where used at login, it would fail.

The problem i had was that if the person who was logged in shut down the browser without logging out properly, it wasnt updating the database. Then i get a phone call from that person and i would have to reset the value to 0 in the database.

This isn't feasible going forward as the product is being rolled out to around 20 people internally soon.

**What I need**

What i need is to find a way that when the browser closes a script gets executed to update the database. Alternatively a way of reading every current session on the server, which i could manipulate, or something else.

**Restrictions**

Our hosting providers are awful and subsequently what changes i can make to the server are limited/impossible. The hosting is a shared hosting solution.