Hi,

>I need to perform some metadata changes in a database, and is better to be
>the only user connected.
>Is there a way to login and change to single user mode?

look at FB 2.1 release notes for 'Database Shutdown Modes'

http://www.firebirdsql.org/rlsnotesh/rlsnotes210.html#rnfb20x-new-shutdown-modes


Regards,
Anderson Farias