The way to start an in-memory recording today is to use -XX:FlightRecorderOptions=defaulrecording=true. With JEP C148, we removed the default recording concept and the way to start an in-memory recording now is -XX:StartFlightRecording=disk=false,

To ease the transition to JDK 9, we should tell the user that they can use the -XX:StartFlightRecording instead, if they use -XX:FlightRecorderOptions=defaulrecording=true