<<I'm trying to create a new database, but after typing the "create database" command followed by the path and filename, hitting Enter and then typing in my username and password (the only user is sysdba and I did change the password) I get the following error message:
Statement failed, SQLSTATE = 08006
Can not access lock files directory /tmp/firebird/>>

You can add your user to the firebird group (without using an
ip address or local host you are effectively using firebird in local mode).
Addin your user to the firebird group means that you can access the tmp files
created when firebird starts up.

Or you can rm /tmp/firebird and then access firebird locally via your user
all the time. The new tmp files will be owned by you. Access remotely will be
a problem though.

Or use an ip address or localhost to create the database.

Paul