OEM grid control 11g  Maintenance : 

Start : 

$MIDDLEWARE_HOME/oms11g/bin/emctl  start oms 

Ex :server :marble.nmhc.com 

cd  /u01/app/oracle/middleware/oms11g/bin

./emctl start oms 

Stop : 

$MIDDLEWARE_HOME/oms11g/bin/emctl stop oms 

Ex : 

cd  /u01/app/oracle/middleware/oms11g/bin

./emctl stop oms

Log files : 

<EM_INSTANCE_BASE>/em/<OMS_NAME>/sysman/log 

Ex : 

/u01/app/oracle/gc_inst/em/EMGC_OMS1/sysman/log

emoms.log

emctl.log

emoms.trc