Hi

> Is there any way to find out how many users are connected to the DB?

You can get user list from service API if use SuperServer.
If you use ClassicServer you cannot get list connected user.

> Or, just to know if there is any user connected to the BD at the moment?

In classic server you can see process. But you can't split diferent DB in this case.

> I need to use GBAK to backup and restore the DB in my application, but I
> need to do this with nobody using the DB, so I need to find out if there
> someone connected and warn the user to disconnect.

You can restore and backup DB with worked user. Fierbird not lock DB file. I recommend restore DB in temporary file, and It rename to final DB name after good restore.

WBR Eugeney Putilin.