JSTATD(1)

✨ jstatd · JSTATD(1) · JDK Commands ✨

okay so bestie, this is the whole jstatd situation: it’s an experimental little RMI server situation, and we’re gonna go through every flag, every warning, and every example together. no skipping, no cap 💅

💖 NAME 💖

jstatd — monitor the creation and termination of instrumented Java HotSpot VMs. That’s the name-section vibe check, periodt.

🌸 SYNOPSIS 🌸

Note: This command is experimental and unsupported.

jstatd [options]

• options — this represents the jstatd command-line options. See Options for the jstatd Command.

🦋 DESCRIPTION 🦋

The jstatd command is an RMI server application that monitors for the creation and termination of instrumented Java HotSpot VMs and provides an interface to enable remote monitoring tools, jstat and jps, to attach to JVMs that are running on the local host and collect information about the JVM process. iconic behavior, honestly.

The jstatd server requires an RMI registry on the local host. The jstatd server attempts to attach to the RMI registry on the default port, or on the port you specify with the -p port option. If an RMI registry isn’t found, then one is created within the jstatd application that’s bound to the port that’s indicated by the -p port option or to the default RMI registry port when the -p port option is omitted. You can stop the creation of an internal RMI registry by specifying the -nr option.

💅 OPTIONS FOR THE JSTATD COMMAND 💅

• -nr — this option does not attempt to create an internal RMI registry within the jstatd process when an existing RMI registry isn’t found.
• -p port — this option sets the port number where the RMI registry is expected to be found, or when not found, created if the -nr option isn’t specified.
• -r rmiport — this option sets the port number to which the RMI connector is bound. If not specified a random available port is used.
• -n rminame — this option sets the name to which the remote RMI object is bound in the RMI registry. The default name is JStatRemoteHost. If multiple jstatd servers are started on the same host, then the name of the exported RMI object for each server can be made unique by specifying this option. However, doing so requires that the unique server name be included in the monitoring client’s hostid and vmid strings.
• -Joption — this option passes a Java option to the JVM, where the option is one of those described on the reference page for the Java application launcher. For example, -J-Xms48m sets the startup memory to 48 MB. See java.

🔐 SECURITY (read this, bestie) 🔐

The jstatd server can monitor only JVMs for which it has the appropriate native access permissions. Therefore, the jstatd process must be running with the same user credentials as the target JVMs. Some user credentials, such as the root user in Linux and macOS operating systems, have permission to access the instrumentation exported by any JVM on the system. A jstatd process running with such credentials can monitor any JVM on the system, but introduces additional security concerns.

The jstatd server doesn’t provide any authentication of remote clients. Therefore, running a jstatd server process exposes the instrumentation export by all JVMs for which the jstatd process has access permissions to any user on the network. This exposure might be undesirable in your environment, and therefore, local security policies should be considered before you start the jstatd process, particularly in production environments or on networks that aren’t secure.

For security purposes, the jstatd server uses an RMI ObjectInputFilter to allow only essential classes to be deserialized.

If your security concerns can’t be addressed, then the safest action is to not run the jstatd server and use the jstat and jps tools locally. However, when using jps to get a list of instrumented JVMs, the list will not include any JVMs running in docker containers.

🛰️ REMOTE INTERFACE 🛰️

The interface exported by the jstatd process is proprietary and guaranteed to change. Users and developers are discouraged from writing to this interface. like, do not build your whole personality on it, bestie 😭

🎀 EXAMPLES 🎀

The following are examples of the jstatd command. The jstatd scripts automatically start the server in the background.

🧚 INTERNAL RMI REGISTRY 🧚

This example shows how to start a jstatd session with an internal RMI registry. This example assumes that no other server is bound to the default RMI registry port (port 1099).

jstatd

🦋 EXTERNAL RMI REGISTRY 🦋

This example starts a jstatd session with an external RMI registry.

rmiregistry&
jstatd

This example starts a jstatd session with an external RMI registry server on port 2020.

jrmiregistry 2020&
jstatd -p 2020

This example starts a jstatd session with an external RMI registry server on port 2020 and JMX connector bound to port 2021.

jrmiregistry 2020&
jstatd -p 2020 -r 2021

This example starts a jstatd session with an external RMI registry on port 2020 that’s bound to AlternateJstatdServerName.

rmiregistry 2020&
jstatd -p 2020 -n AlternateJstatdServerName

💀 STOP THE CREATION OF AN IN-PROCESS RMI REGISTRY 💀

This example starts a jstatd session that doesn’t create an RMI registry when one isn’t found. This example assumes an RMI registry is already running. If an RMI registry isn’t running, then an error message is displayed.

jstatd -nr

🔥 ENABLE RMI LOGGING 🔥

This example starts a jstatd session with RMI logging capabilities enabled. This technique is useful as a troubleshooting aid or for monitoring server activities.

jstatd -J-Djava.rmi.server.logCalls=true

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— xoxo, your Unix bestie 💅 · JDK 23 · 2024