trigger to restrict users

[julian]

I use this trigger in one of my databases:

CREATE OR REPLACE TRIGGER logon_from_linux
AFTER
ON
REFERENCING NEW AS NEW OLD AS OLD
declare
W_NAME varchar2(20);
W_IP   varchar2(20);
begin
 select Sys_Context('USERENV','SESSION_USER') into W_NAME from dual;
 select Sys_Context('USERENV','IP_ADDRESS') into W_IP from dual;
     if W_NAME != 'LARRY' and W_IP = '567.79.117.6' then
        insert into LINUX_LOGIN values(W_NAME,W_IP,sysdate);
        RAISE_APPLICATION_ERROR(-20111, 'Sorry, you are not allowed here!');
     end if;
end;
/