root@doos2-comp:/home/doos# /opt/firebird/bin/isql
Use CONNECT or CREATE DATABASE to specify a database
SQL> connect 'security.db' user sysdba password 'masterkey';
Database: 'security.db', User: SYSDBA
SQL> create user sysdba password 'masterkey' using plugin Legacy_UserManager;
Statement failed, SQLSTATE = HY000
Missing requested management plugin

SQL> create user sysdba password 'masterkey' using plugin Legacy_UserManager;
Statement failed, SQLSTATE = 23000
add record error
-violation of PRIMARY or UNIQUE KEY constraint "INTEG_2" on table "PLG$USERS"
-Problematic key value is ("PLG$USER_NAME" = 'SYSDBA')