[oracle@oratest03 scripts]$ emctl start dbconsole
Environment variable ORACLE_UNQNAME not defined. Please set ORACLE_UNQNAME to database unique name.
[oracle@oratest03 scripts]$
[oracle@oratest03 scripts]$ export ORACLE_UNQNAME=T11R2
[oracle@oratest03 scripts]$ emctl start dbconsole
OC4J Configuration issue. /app/oracle/product/11.2.0.1/oc4j/j2ee/OC4J_DBConsole_oratest03_T11R2 not found.

This is due to a misconfiguration of dbconsole during database setup. The fastest solution is usually to recreate repository and configuration.

First, deconfigure dbconsole:

[oracle@oratest03 bin]$ ./emca -deconfig dbcontrol db -repos drop

STARTED EMCA at Dec 28, 2009 12:15:33 PM
EM Configuration Assistant, Version 11.2.0.0.2 Production
Copyright (c) 2003, 2005, Oracle.  All rights reserved.

Enter the following information:
Database SID: T11R2
Listener port number: 1521
Password for SYS user:
Password for SYSMAN user:  

Do you wish to continue? [yes(Y)/no(N)]: Y
Dec 28, 2009 12:15:44 PM oracle.sysman.emcp.EMConfig perform
INFO: This operation is being logged at /app/oracle/cfgtoollogs/emca/T11R2/emca_2009_12_28_12_15_32.log.
Dec 28, 2009 12:15:44 PM oracle.sysman.emcp.EMDBPreConfig performDeconfiguration
WARNING: EM is not configured for this database. No EM-specific actions can be performed.
Dec 28, 2009 12:15:45 PM oracle.sysman.emcp.EMReposConfig invoke
INFO: Dropping the EM repository (this may take a while) ...
Dec 28, 2009 12:17:33 PM oracle.sysman.emcp.EMReposConfig invoke
INFO: Repository successfully dropped
Enterprise Manager configuration completed successfully
FINISHED EMCA at Dec 28, 2009 12:17:33 PM

Now, let’s configure it again

[oracle@oratest03 bin]$ ./emca -config dbcontrol db -repos create                                          

STARTED EMCA at Dec 28, 2009 12:17:43 PM
EM Configuration Assistant, Version 11.2.0.0.2 Production
Copyright (c) 2003, 2005, Oracle.  All rights reserved.

Enter the following information:
Database SID: T11R2
Listener port number: 1521
Listener ORACLE_HOME [ /app/oracle/product/11.2.0.1 ]:
Password for SYS user:
Password for DBSNMP user:
Password for SYSMAN user:
Email address for notifications (optional):
Outgoing Mail (SMTP) server for notifications (optional):
-----------------------------------------------------------------

You have specified the following settings

Database ORACLE_HOME ................ /app/oracle/product/11.2.0.1

Local hostname ................ oratest03
Listener ORACLE_HOME ................ /app/oracle/product/11.2.0.1
Listener port number ................ 1521
Database SID ................ T11R2
Email address for notifications ...............
Outgoing Mail (SMTP) server for notifications ............... 

-----------------------------------------------------------------
Do you wish to continue? [yes(Y)/no(N)]: Y
Dec 28, 2009 12:17:58 PM oracle.sysman.emcp.EMConfig perform
INFO: This operation is being logged at /app/oracle/cfgtoollogs/emca/T11R2/emca_2009_12_28_12_17_43.log.
Dec 28, 2009 12:17:59 PM oracle.sysman.emcp.EMReposConfig createRepository
INFO: Creating the EM repository (this may take a while) ...
Dec 28, 2009 12:23:44 PM oracle.sysman.emcp.EMReposConfig invoke
INFO: Repository successfully created
Dec 28, 2009 12:23:47 PM oracle.sysman.emcp.EMReposConfig uploadConfigDataToRepository
INFO: Uploading configuration data to EM repository (this may take a while) ...
Dec 28, 2009 12:24:41 PM oracle.sysman.emcp.EMReposConfig invoke
INFO: Uploaded configuration data successfully
Dec 28, 2009 12:24:43 PM oracle.sysman.emcp.util.DBControlUtil configureSoftwareLib
INFO: Software library configured successfully.
Dec 28, 2009 12:24:43 PM oracle.sysman.emcp.EMDBPostConfig configureSoftwareLibrary
INFO: Deploying Provisioning archives ...
Dec 28, 2009 12:25:13 PM oracle.sysman.emcp.EMDBPostConfig configureSoftwareLibrary
INFO: Provisioning archives deployed successfully.
Dec 28, 2009 12:25:13 PM oracle.sysman.emcp.util.DBControlUtil secureDBConsole
INFO: Securing Database Control (this may take a while) ...
Dec 28, 2009 12:25:54 PM oracle.sysman.emcp.util.DBControlUtil secureDBConsole
INFO: Database Control secured successfully.
Dec 28, 2009 12:25:54 PM oracle.sysman.emcp.util.DBControlUtil startOMS
INFO: Starting Database Control (this may take a while) ...
Dec 28, 2009 12:26:19 PM oracle.sysman.emcp.EMDBPostConfig performConfiguration
INFO: Database Control started successfully
Dec 28, 2009 12:26:19 PM oracle.sysman.emcp.EMDBPostConfig performConfiguration
INFO: >>>>>>>>>>> The Database Control URL is https://oratest03:1158/em <<<<<<<<<<<
Dec 28, 2009 12:26:25 PM oracle.sysman.emcp.EMDBPostConfig invoke
WARNING:
************************  WARNING  ************************

Management Repository has been placed in secure mode wherein Enterprise Manager data will be encrypted.  The encryption key has been placed in the file: /app/oracle/product/11.2.0.1/oratest03_T11R2/sysman/config/emkey.ora.   Please ensure this file is backed up as the encrypted data will become unusable if this file is lost. 

***********************************************************
Enterprise Manager configuration completed successfully
FINISHED EMCA at Dec 28, 2009 12:26:25 PM

That’s all. Remember, if you want or need, to backup you encryption key.