Enterprise Manager DB Control/DB Console (OEM) is not working after Changing Hostname or IP Address

Step 1. Set $ORACLE_HOSTNAME to the old hostname

  
export ORACLE_HOSTNAME=old_name

Step 2. De-configure the old DB Console by running the following command:

  
$ORACLE_HOME/bin/emca -deconfig dbcontrol db

Step 3. $ORACLE_HOSTNAME to the new hostname:

export ORACLE_HOSTNAME=new_name

Step 4. Configure the new DB Console

$ORACLE_HOME/bin/emca -config dbcontrol db -repos recreate