WebLogic Startup fails with Unable to obtain lock on Server may already be running

Issue : When weblogic server starting showing error "Unable to obtain lock" .
Root Cause: previous session has not been terminated cause <servername>.lok file exists

Solution:
-Go to>> $DOMAIN_HOME/servers/<servername>/tmp/
  Check <servername>.lok file exists in this location.
-Delete this <servername>.lok file and start admin server ,it will overcome the error ...

Note-this solution applicable for all managed server as well..