OMS service runs on the server, where oracle 12c cloud control is installed. We can use EMCTL utility to stop and restart OMS service.

cd $OMS_HOME/bin

Stopping OMS:

 oracle@test:…ta/app/oracle/oms12cr5/oms/bin$ ./emctl stop oms

Oracle Enterprise Manager Cloud Control 12c Release 5

Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved. Stopping WebTier...

WebTier Successfully Stopped Stopping Oracle Management Server...

Oracle Management Server Successfully Stopped
Oracle Management Server is Down

Starting OMS:

 
oracle@test:…ta/app/oracle/oms12cr5/oms/bin$ ./emctl start oms

Oracle Enterprise Manager Cloud Control 12c Release 5

Copyright (c) 1996, 2015 Oracle Corporation. All rights reserved. Starting Oracle Management Server...

Starting WebTier...
WebTier Successfully Started

Oracle Management Server Successfully Started
Oracle Management Server is Up

Checking the OMS status:

oracle@test:…ta/app/oracle/oms12cr5/oms/bin$ ./emctl status oms

Oracle Enterprise Manager Cloud Control 12c Release 5
Copyright (c) 1996, 2015 Oracle Corporation.	All rights reserved.
WebTier is Up
Oracle Management Server is Up