Enterprise Manager Configuration Assistant - Oracle 10g/11g Data and Database Management Utilities - page 332

Enterprise Manager configuration
Most DBA's have the EM automatically configured by the time Oracle creates a
database with the DBCA. The default port assigned is 1158, but if ever the DBA
needs to create and configure an additional database on the same host the default
assigned port will be 5500, then 5501 and so on. After the RDBMS installation you
should read the portlist.ini file located at <Oracle Home>/install/portlist.
ini for details on ports assigned by Oracle. The easiest way to configure EM is
with the DBCA, but this is the least customizable way to do it. You can have EM
configured in a fully customizable fashion using the EMCA command line.
How to find out if the console components are
currently installed
You can easily find out if your current Oracle installation includes the Enterprise
Manager DB control console components installed by querying the installation
with the opatch tool. The command used to find out if the console components are
installed is:
<Oracle Home>/opatch lsinventory -detail
Then look for the following entries:
Enterprise Manager Agent Core
Enterprise Manager Agent DB
Enterprise Manager Baseline
Enterprise Manager Common Files
Enterprise Manager Minimal Integration
Enterprise Manager plugin Common Files
Enterprise Manager plugin Common Files
Enterprise Manager Repository Core
Enterprise Manager Repository DB
Oracle Enterprise Manager Console DB
This output corresponds to an Oracle 10g Rel. 2 Oracle Home, meanwhile
the following output corresponds to an Oracle 11g Rel. 1 Oracle Home.
Enterprise Manager Agent
Enterprise Manager Agent Core Files
Enterprise Manager Common Core Files
Enterprise Manager Common Files
Enterprise Manager Database Plugin -- Agent Support
Enterprise Manager Database Plugin -- Management Service Support