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Chapter 2

Monitoring and Management Using JMX Technology

The Java virtual machine (Java VM) has built-in instrumentation that enables you to monitor and manage it using the Java Management Extensions (JMX) technology. These built-in management utilities are often referred to as out-of-the-box management tools for the Java VM. You can also monitor any appropriately instrumented applications using the JMX API. 

Setting System Properties

To enable and configure the out-of-the-box JMX agent so that it can monitor and manage the Java VM, you must set certain system properties when you start the Java VM. You set a system property on the command-line as follows.

java -Dproperty=value ...

You can set any number of system properties in this way. If you do not specify a value for a management property, then the property is set with its default value. The full set of out-of-the-box management properties is described in Table 2-1 at the end of this chapter. You can also set system properties in a configuration file, as described in Out-of-the-Box Monitoring and Management Properties.

Note - To run the Java VM from the command line, you must add JRE_HOME/bin to your path, where JRE_HOME is the directory containing the Java Runtime Environment (JRE) implementation. Alternatively, you can enter the full path when you type the command.

The following documents describe the syntax and the full set of command-line options supported by the Java HotSpot VMs.

Enabling the Out-of-the-Box Management

To monitor a Java platform using the JMX API, you must do the following.

  1. Enable the JMX agent (another name for the platform MBean server) when you start the Java VM. You can enable the JMX agent for:

    • Local monitoring, for a client management application running on the local system.

    • Remote monitoring, for a client management application running on a remote system.

  2. Monitor the Java VM with a tool that complies to the JMX specification, such as JConsole. See Chapter 3, Using JConsole for more information about Console.

These steps are described in the next sections.

Local Monitoring and Management

Under previous releases of the Java SE platform, to allow the JMX client access to a local Java VM, you had to set the following system property when you started the Java VM or Java application.

com.sun.management.jmxremote

Setting this property registered the Java VM platform's MBeans and published the Remote Method Invocation (RMI) connector via a private interface to allow JMX client applications to monitor a local Java platform, that is, a Java VM running on the same machine as the JMX client.

In the Java SE 6 platform, it is no longer necessary to set this system property. Any application that is started on the Java SE 6 platform will support the Attach API, and so will automatically be made available for local monitoring and management when needed.

For example, previously, to enable the JMX agent for the Java SE sample application Notepad, you would have to run the following commands.

% cd JDK_HOME/demo/jfc/Notepad
% java -Dcom.sun.management.jmxremote -jar Notepad.jar

In the above command, JDK_HOME is the directory in which the Java Development Kit (JDK) is installed. In the Java SE 6 platform, you would simply have to run the following command to start Notepad.

% java -jar Notepad.jar

Once Notepad has been started, a JMX client using the Attach API can then enable the out-of-the-box management agent to monitor and manage the Notepad application.

Note - On Windows platforms, for security reasons, local monitoring and management is only supported if your default temporary directory is on a file system that allows the setting of permissions on files and directories (for example, on a New Technology File System (NTFS) file system). It is not supported on a File Allocation Table (FAT) file system, which provides insufficient access controls.

Local Monitoring and Management Using JConsole

Local monitoring with JConsole is useful for development and creating prototypes. Using JConsole locally is not recommended for production environments, because JConsole itself consumes significant system resources. Rather, you should use JConsole on a remote system to isolate it from the platform being monitored.

However, if you do wish to perform local monitoring using JConsole, you start the tool by typing jconsole in a command shell. When you start jconsole without any arguments, it will automatically detect all local Java applications, and display a dialog box that enables you to select the application you want to monitor. Both JConsole and the application must by executed by the same user, since the monitoring and management system uses the operating system's file permissions.

Note - To run JConsole from the command line, you must add JDK_HOME/bin to your path. Alternatively, you can enter the full path when you type the command.

For more information, see Chapter 3, Using JConsole.

Remote Monitoring and Management

To enable monitoring and management from remote systems, you must set the following system property when you start the Java VM.

com.sun.management.jmxremote.port=portNum

In the property above, portNum is the port number through which you want to enable JMX RMI connections. Be sure to specify an unused port number. In addition to publishing an RMI connector for local access, setting this property publishes an additional RMI connector in a private read-only registry at the specified port using a well known name, "jmxrmi".

Note - You must set the above system property in addition to any properties you might set for security.

Remote monitoring and management requires security to ensure that unauthorized persons cannot control or monitor your application. Password authentication over the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) is enabled by default. You can disable password authentication and SSL separately, as described in the next sections.

Note - For production systems, use both SSL client certificates to authenticate the client host and password authentication for user management. See the topics Using SSL and Using LDAP Authentication for more information.