{TAIL ~ The controller} sends the file update information to the agent, and {HEAD ~ the agent} requests the controller to retrieve file updates 
{ TAIL ~ The controller } sends the file update information to the agent , and { HEAD ~ the agent } requests the controller to retrieve file updates
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH