> How can I know who is conencted to a database?

On SuperServer, you can get a list of the usernames that are connected
to your database. On ClassicServer this list will only "see" your own
connection.

It depends on your client lib. IBObjects for Delphi, for example, has
a property TIB_Connection.Users, which delivers this list.

> And is there any chance to kick them out? Excluded Database shutdown
> of course.

No. No chance to kick them out except a database or service shutdown.
This, IMHO, is one of the weaknesses of Firebird. But AFAIK the team
is working on them.

Best Regards

Stefan