Oracle : Start the Oracle Intelligent Agent

One needs to start an OIA (Oracle Intelligent Agent) process on all machines that will to be managed via OEM.

For OEM 9i and above:
agentctl start agent
agentctl stop agent

For OEM 2.1 and below:
lsnrctl dbsnmp_start
lsnrctl dbsnmp_status

On Windows NT, start the "OracleAgent" Service.
If the agent doesn't want to start, ensure your environment variables are set correctly and delete the following files before trying again:
1) In $ORACLE_HOME/network/admin: snmp_ro.ora and snmp_rw.ora.
2) Also delete ALL files in $ORACLE_HOME/network/agent/.