Create Trigger to Monitor Database Errors

First, we have to create a table where the errors are stored, but make sure it's a use who has global rights on the database:

CREATE TABLE error_log (
  server_error VARCHAR2(100),
  osuser VARCHAR2(30),
  username VARCHAR2(30),
  machine VARCHAR2(64),
  process VARCHAR2(24),
  program VARCHAR2(48),
  stmt VARCHAR2(4000),
  msg VARCHAR2(4000),
  date_created DATE  
);

After we've created the table, we simply add a trigger with is fired by "AFTER SERVERERROR ON DATABASE":

CREATE OR REPLACE
TRIGGER error_log_trigger 
 AFTER SERVERERROR ON DATABASE
DECLARE
 username_  error_log.username%TYPE;
 osuser_    error_log.osuser%TYPE;
 machine_   error_log.machine%TYPE;
 process_   error_log.process%TYPE;
 program_   error_log.program%TYPE;
  stmt_      VARCHAR2(4000);
  msg_       VARCHAR2(4000);
  sql_text_  ora_name_list_t;
BEGIN
   FOR i IN 1..NVL(ora_sql_txt(sql_text_), 0) LOOP  
    stmt_ := SUBSTR(stmt_ || sql_text_(i) ,1,4000);
  END LOOP;
   FOR i IN 1..ora_server_error_depth LOOP
    msg_ := SUBSTR(msg_ || ora_server_error_msg(i) ,1,4000);
  END LOOP;
   SELECT osuser, username, machine, process, program
  INTO   osuser_, username_, machine_, process_, program_
  FROM   sys.v_$session
  WHERE  audsid = USERENV('SESSIONID');
   INSERT INTO error_log VALUES (dbms_standard.server_error(1), osuser_, username_, machine_, process_, program_, stmt_, msg_, SYSDATE);
END;