Start in Oracle 10g, Oracle start to use web base Enterprise Manager (EM).

But if you try to configure the EM for Oracle database 10g (10.2.0.4 and 10.2.0.5) AFTER 31 December 2010, you will fail.
Confirm!!!!
Why?:
If you plan to configure Database Control with either of these Oracle Database releases, Oracle strongly recommends that you apply Patch 8350262 to your Oracle Home installations before you configure Database Control. Configuration of Database Control is typically done when you create or upgrade Oracle Database, or if you run Enterprise Manager Configuration Assistant (EMCA) in standalone mode.
Yes, you need to patch your database with patch 8350262. If not, you will encounter an error during the configuration process.
Nothing to worry, the patch is just a small Opatch, and no downtime is required. It also don’t effect existing Oracle database control configuration.
How to patch?
export ORACLE_HOME=/u01/app/../db_1set ORACLE_HOME=C:\..\db_1
bash-3.00$ /u01/app/../db_1/OPatch/opatch applyVerifying the update...
Inventory check OK: Patch ID 8350262 is registered in Oracle Home inventory with proper meta-data.
Files check OK: Files from Patch ID 8350262 are present in Oracle Home.
OPatch succeeded.
./killDBConsole scriptemctl secure dbconsole -reset emctl start dbconsole Sample of errors that required this patch:
Could not complete the Enterprise Manager configuration.
Enterprise manager configuration failed due to the following error:
Error starting Database Control
CONFIG: Securing Database Control completed successfully .
Jan 2, 2011 7:22:47 PM oracle.sysman.emcp.ParamsManager getParam
CONFIG: No value was set for the parameter ORACLE_HOSTNAME.
Jan 2, 2011 7:22:47 PM oracle.sysman.emcp.util.DBControlUtil startOMS
INFO: Starting Database Control (this may take a while) ...
Jan 2, 2011 7:22:47 PM oracle.sysman.emcp.util.PlatformInterface addEnvVarToList
CONFIG: Value for env var 'ORACLE_HOSTNAME' is '', discarding the same
CONFIG: Returning env array from cache
Jan 2, 2011 7:22:47 PM oracle.sysman.emcp.util.PlatformInterface executeCommand
CONFIG: Starting execution: /myhost/bin/emctl start dbconsole
Jan 2, 2011 7:27:26 PM oracle.sysman.emcp.util.PlatformInterface executeCommand
CONFIG: Exit value of 1
Jan 2, 2011 7:27:26 PM oracle.sysman.emcp.util.PlatformInterface executeCommand
CONFIG: Oracle Enterprise Manager 10g Database Control Release 10.2.0.4.0
Copyright (c) 1996, 2007 Oracle Corporation. All rights reserved.
https://myhost:5501/em/console/aboutApplication
Starting Oracle Enterprise Manager 10g Database Control
............................................................................................. failed.
------------------------------------------------------------------
Logs are generated in directory /myhost/sysman/log
Jan 2, 2011 7:27:26 PM oracle.sysman.emcp.util.PlatformInterface executeCommand
WARNING: Error executing /myhost/bin/emctl start dbconsole
Jan 2, 2011 7:27:26 PM oracle.sysman.emcp.EMConfig perform
SEVERE: Error starting Database Control
Refer to the log file at /myhost/dbua/d4/upgrade/emConfig.log for more details.
Jan 2, 2011 7:27:26 PM oracle.sysman.emcp.EMConfig perform
CONFIG: Stack Trace:
oracle.sysman.emcp.exception.EMConfigException: Error starting Database Control
at oracle.sysman.emcp.EMDBPostConfig.performUpgrade(EMDBPostConfig.java:763)
at oracle.sysman.emcp.EMDBPostConfig.invoke(EMDBPostConfig.java:232)
at oracle.sysman.emcp.EMDBPostConfig.invoke(EMDBPostConfig.java:193)
at oracle.sysman.emcp.EMConfig.perform(EMConfig.java:184)
at oracle.sysman.assistants.util.em.EMConfiguration.run(EMConfiguration.java:436)
at oracle.sysman.assistants.util.em.EMConfigStep.executeImpl(EMConfigStep.java:140)
at oracle.sysman.assistants.util.step.BasicStep.execute(BasicStep.java:210)
at oracle.sysman.assistants.util.step.BasicStep.callStep(BasicStep.java:251)
at oracle.sysman.assistants.dbma.backend.EMConfigStep.executeStepImpl(EMConfigStep.java:104)
at oracle.sysman.assistants.dbma.backend.SummarizableStep.executeImpl(SummarizableStep.java:175)
at oracle.sysman.assistants.util.step.BasicStep.execute(BasicStep.java:210)
at oracle.sysman.assistants.util.step.Step.execute(Step.java:140)
at oracle.sysman.assistants.util.step.StepContext$ModeRunner.run(StepContext.java:2488)
at java.lang.Thread.run(Thread.java:534)
$ bin/emca -config dbcontrol db -repos recreate -cluster
STARTED EMCA at Jan 11, 2011 4:11:01 PM
EM Configuration Assistant, Version 10.2.0.1.0 Production
Copyright (c) 2003, 2005, Oracle. All rights reserved.
Enter the following information:
Database unique name: catest
Database Control is already configured for the database catest
You have chosen to configure Database Control for managing the database catest
This will remove the existing configuration and the default settings and perform a fresh configuration
Do you wish to continue? [yes(Y)/no(N)]: Y
Listener port number: 1521
Cluster name: mycluster
Password for SYS user:
Password for DBSNMP user:
Password for SYSMAN user:
Email address for notifications (optional):
Outgoing Mail (SMTP) server for notifications (optional):
……..
Jan 11, 2011 4:18:05 PM oracle.sysman.emcp.util.DBControlUtil secureDBConsole
INFO: Securing Database Control (this may take a while) ...
Jan 11, 2011 4:19:31 PM oracle.sysman.emcp.util.DBControlUtil startOMS
INFO: Starting Database Control (this may take a while) ...
Jan 11, 2011 4:28:38 PM oracle.sysman.emcp.EMConfig perform
SEVERE: Error starting Database Control
Refer to the log file at /myhost/oracle/product/10.2.0/db_1/cfgtoollogs/emca/catest/emca_2011-01-11_
04-11-01-PM.log for more details.
Could not complete the configuration. Refer to the log file at /myhost/oracle/product/10.2.0/db_
1/cfgtoollogs/emca/catest/emca_2011-01-11_04-11-01-PM.log for more details.
Could not complete the Enterprise Manager configuration.
Enterprise manager configuration failed due to the following error:
Error starting Database Control
database error, Oracle, Oracle Enterprise Manager Oracle, Software