Submitted by: @sim1984

recreate table att_log (att_id int, att_name varchar(50), att_user varchar(31), att_addr varchar(25), att_prot varchar(15), att_auth varchar(15), att_dts timestamp default 'now');

commit;

set term ^;
create or alter trigger trg_connect active on connect as
begin
in autonomous transaction do
insert into att_log(att_id, att_name, att_user, att_addr, att_prot, att_auth)
select
mon$attachment_id
,mon$attachment_name
,mon$user
,mon$remote_address
,mon$remote_protocol
,mon$auth_method
from mon$attachments
--where mon$attachment_id = current_connection
;
end
^
set term ;^
commit;

quit;

If you try to make a backup

gbak -b localhost/3333:C:\FBTESTING\qa\fbt-repo\tmp\E30.fdb C:\FBTESTING\qa\fbt-repo\tmp\E30.fbk

gbak: ERROR:INSERT operation is not allowed for system table ATT_LOG
gbak: ERROR: At trigger 'TRG_CONNECT' line: 4, col: 3
gbak:Exiting before completion due to errors

or

fbsvcmgr localhost:service_mgr action_backup dbname C:\FBTESTING\qa\fbt-repo\tmp\E30.fdb bkp_file C:\FBTESTING\qa\fbt-repo\tmp\E30.fbk

INSERT operation is not allowed for system table ATT_LOG
-At trigger 'TRG_CONNECT' line: 4, col: 3
-Exiting before completion due to errors

Commits: 2a1d6e2 10d3c38 FirebirdSQL/fbt-repository@e9fa8e5 FirebirdSQL/fbt-repository@5710a08