Grid Control

Definitions

OMS - Management Service - This is responsible for communicating with the user via a GUI and communicating with the OMR
OMR - Management Repository - This is a collection of tables owned by the sysman schema that stores all the data collected by the OMA
OMA - Management Agent - This is a perl program that runs on the database host (one for all databases on the host) and uploads data to the OMS

From SQL*Plus:
select username,program from v$session where LOWER (program) like 'emagent%';

If no rows selected, the agent is not running. or

From Unix:
. oraenv
agent11g (how to find what SIDs are available on your machine)
emctl status agent

ps -ef|grep [a]gent

There should be 2 processes. If only 1, kill it and restart the agent.

emctl start agent