Command Reference

A.1 Command-Line Options

When you launch your Java application with the java command, you can specify options to enable Java Flight Recorder, configure its settings, and start a recording. The following command-line options are specific to Java Flight Recorder:

-XX:+|-FlightRecorder
-XX:FlightRecorderOptions
-XX:StartFlightRecording

These command-line options are available only in the commercial license of the JDK. To use them, you have to also specify the -XX:+UnlockCommercialFeatures option.

For more information about these options, see Java Command Line Reference at http://docs.oracle.com/javase/8/docs/technotes/tools/unix/java.html (UNIX)
http://docs.oracle.com/javase/8/docs/technotes/tools/windows/java.html (Windows)

Note:

You should use -XX options only if you have a thorough understanding of your system. If you use these commands improperly, you might affect the stability or performance of your system. -XX options are experimantal, and they are subject to change at any time.

A.2 Diagnostic Command Reference

This is a description of the diagnostic commands available to control Java Flight Recorder and the parameters available for each command. This information is also available by running the jcmd command with the process identifier specified, followed by the help parameter and the commad name. For example, to get help information for the JFR.start command on a running JVM process with the identifier 5361, run the following:

jcmd 5361 help JFR.start

To get a full list of diagnostic commands available to the JVM, do not specify the name of the command. For more information about using the jcmd command, see the jcmd documentation at:

http://docs.oracle.com/javase/8/docs/technotes/tools/windows/jcmd.html

The diagnostic commands associated with Java Flight Recorder are:

JFR.start
JFR.check
JFR.stop
JFR.dump

A.2.1 JFR.start

The JFR.start diagnostic command starts a flight recording. Table A-1 lists the parameters you can use with this command.

Table A-1 JFR.start

Parameter	Description	Type of value	Default
name	Name of recording	String
settings	Server-side template	String
defaultrecording	Starts default recording	Boolean	False
delay	Delay start of recording	Time	0s
duration	Duration of recording	Time	0s (means "forever")
filename	Resulting recording filename	String
compress	GZip compress the resulting recording file	Boolean	False
maxage	Maximum age of buffer data	Time	0s (means "no age limit")
maxsize	Maximum size of buffers in bytes	Long	0 (means "no max size")

A.2.2 JFR.check

The JFR.check command shows information about running recordings. Table A-2 lists the parameters you can use with this command.

Table A-2 JFR.check

Parameter	Description	Type of value	Default
name	Recording name	String
recording	Recording id	Long	1
verbose	Print verbose data	Boolean	False

A.2.3 JFR.stop

The JFR.stop diagnostic command stops running flight recordings. Table A-3 lists the parameters you can use with this command.

Table A-3 JFR.stop

Parameter	Description	Type of value	Default
name	Recording name	String
recording	Recording id	Long	1
discard	Discards the recording data	Boolean
copy_to_file	Copy recording data to file	String
compress_copy	GZip compress "copy_to_file" destination	Boolean	False

A.2.4 JFR.dump

The JFR.dump diagnostic command stops running flight recordings. Table A-4 lists the parameters you can use with this command.

Table A-4 JFR.dump

Parameter	Description	Type of value	Default
name	Recording name	String
recording	Recording id	Long	1
copy_to_file	Copy recording data to file	String
compress_copy	GZip compress "copy_to_file" destination	Boolean	False