Usually Agent Unreachable status shown when agent is not running so first try to start the agent and wait for sometime that to be reflected in OEM or if you have changed your hostname/IP or timezone of your oracle server then follow up the following steps.
1. emctl resetTZ agent
3. emctl status dbconsole
4. emctl start dbconsole
1. emctl resetTZ agent
Oracle Enterprise Manager 11g Database Control Release 11.2.0.1.0
Copyright (c) 1996, 2010 Oracle Corporation. All rights reserved.
Updating E:\app\Administrator\product\11.2.0\dbhome_1/rajkumar-pc_orcl/sysman/config/
emd.properties...
Successfully updated E:\app\Administrator\product\11.2.0\dbhome_1/rajkumar-pc_orcl/sy
sman/config/emd.properties.
2. Login as the em repository user and run the script:
exec mgmt_target.set_agent_tzrgn('rajkumar-pc:3938','America/New_York')
and commit the changes
SQL> exec mgmt_target.set_agent_tzrgn('rajkumar-pc:3938','America/New_York')
SQL> commit
3. emctl status dbconsole
Oracle Enterprise Manager 11g Database Control Release 11.2.0.1.0
Copyright (c) 1996, 2010 Oracle Corporation. All rights reserved.
EM Daemon is not running.
------------------------------------------------------------------
Logs are generated in directory E:\app\Administrator\product\11.2.0\dbhome_1/COL-OR
A01_orcl/sysman/log
4. emctl start dbconsole
Oracle Enterprise Manager 11g Database Control Release 11.2.0.1.0
Copyright (c) 1996, 2010 Oracle Corporation. All rights reserved.
Starting Oracle Enterprise Manager 11g Database Control ...The OracleDBConsoleor
cl service is starting...................
The OracleDBConsoleorcl service was started successfully.
Enjoy.............................
