1，修改DBSNMP密码：
重新配置DBCONSOLE，需要输入DBSNMP密码，但任何密码都会显示错误，需要预先修改。
sql>alter user dbsnmp identified by xxx;
2，删除早期DBCONSOLE创建的用户：
sql>drop role MGMT_USER; sql>drop user MGMT_VIEW cascade; sql>drop user sysman cascade;
3，删除早期DBCONSOLE创建的对象：
sql>drop PUBLIC SYNONYM MGMT_TARGET_BLACKOUTS; sql>drop public synonym SETEMVIEWUSERCONTEXT;4. 重新创建oem[oracle@rac log]$ emca -config dbcontrol db -repos recreate 或emca -repos recreate -host rac5. 如果创建oem时提示Note: For Desktop Class Install always pass parameter ORACLE_HOSTNAME
as "localhost" to any emca command则：Set ORACLE_HOSTNAME=old_hostname in the environment.
For a single-instance database:
$ $ORACLE_HOME/bin/emca -deconfig dbcontrol db
For Oracle RAC:
$ $ORACLE_HOME/bin/emca -deconfig dbcontrol db -cluster
参考文档：[url]http://docs.oracle.com/cd/E18283_01/server.112/e17120/dbcontrol006.htm