The target agent must be installed.
You must be able to resolve the hostname for the target agent from your OMS server
You must be able to connect on port 3872 (or the port you allocated to AGENT_PORT during Agent Install)
Setup - Add Target - Add Targets Manually
TODO: I have not yet tested this method successfully
echo "add_target -name=\"$(hostname -s)_myListener\" -type=\"oracle_listener\" -host=\"$(hostname)\" -properties=\"LsnrName:myLISTENER;ListenerOraDir:${ORACLE_HOME}/network/admin;Port:1521;OracleHome:${ORACLE_HOME};Machine:$(hostname);\"" > "/tmp/emclicommands.txt"
echo "add_target -name=\"$(hostname -s)_${ORACLE_SID}\" -type=\"oracle_database\" -host=\"$(hostname)\" -credentials=\"UserName:dbsnmp;password:myDBSNMOpwd;Role:Normal\" -properties=\"SID:${ORACLE_SID};Port:1521;OracleHome:${ORACLE_HOME};MachineName:$(hostname);\"" >> "/tmp/emclicommands.txt"
emcli sync
emcli argfile /tmp/emclicommands.txt
rm -rf /tmp/emclicommands.txt