The Backdoor Entry to Oracle Database


I want to talk about a situation that happened to me a few days ago. I Logged in to one of my databases and my connection was hanged. My database was not accepting new connections. Now bound to the database server and I checked the status of the listener.

# lsnrctl status

Everything was normal. The listener is listening to my database. So I didn’t get any error from listener. I tried to log in with “sqlplus / as sysdba” but I failed. Connections on the server was also hanging. I checked the background processes.

# ps -ef | grep ora_

Everything was normal. And I learned something I did not know until that day. The backdoor entry of the Oracle database! You can enter to the database through the back door using SQL * Plus tool with “Prelim” parameter:)  Prelim, directly connects to the SGA but it does not open a session.

You can connect to the database with Prelim as following

# sqlplus -prelim / as sysdba


# sqlplus /nolog
SQL> set _prelim on
SQL> conn / as sysdba
Prelim connection established

Now, you can analyze the SGA using oradebug command.

SQL> oradebug setmypid
SQL> oradebug hanganalyze 12

A trace file will be produced in the directory configured in user_dump_dest parameter. If we are to sort the files according to time we can get the most recent trace file.

# ls -ltrh

You can also get the trace file name with oradebug command.


When we examine the trace file, we see that lines beginning as follows.

*** 2021-11-12 12:14:02.870
instances (db_name.oracle_sid): dbtalip.talipdb
oradebug_node_dump_level: 12
analysis initiated by oradebug

If we continue to examine the trace file We can see the details of the session that caused the problem.
os id: 981
process id: 29, oracle@dbtalip (TNS V1-V3)
session id: 74
session serial #: 47681

When we kill that session from OS, everything will be OK.

# kill -9 981

Talip Hakan Öztürk


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