jdk

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.TH "JSTATD" "1" "2025" "JDK 24-ea" "JDK Commands"
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.hy
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.SH NAME
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.PP
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jstatd - monitor the creation and termination of instrumented Java
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HotSpot VMs
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.SH SYNOPSIS
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.PP
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\f[B]WARNING:\f[R] This command is experimental, unsupported, and
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deprecated.
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It will be removed in a future release.
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.PP
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\f[V]jstatd\f[R] [\f[I]options\f[R]]
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.TP
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\f[I]options\f[R]
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This represents the \f[V]jstatd\f[R] command-line options.
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See \f[B]Options for the jstatd Command\f[R].
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.SH DESCRIPTION
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.PP
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The \f[V]jstatd\f[R] command is an RMI server application that monitors
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for the creation and termination of instrumented Java HotSpot VMs and
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provides an interface to enable remote monitoring tools, \f[V]jstat\f[R]
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and \f[V]jps\f[R], to attach to JVMs that are running on the local host
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and collect information about the JVM process.
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.PP
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The \f[V]jstatd\f[R] server requires an RMI registry on the local host.
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The \f[V]jstatd\f[R] server attempts to attach to the RMI registry on
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the default port, or on the port you specify with the \f[V]-p\f[R]
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\f[V]port\f[R] option.
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If an RMI registry is not found, then one is created within the
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\f[V]jstatd\f[R] application that\[aq]s bound to the port that\[aq]s
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indicated by the \f[V]-p\f[R] \f[V]port\f[R] option or to the default
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RMI registry port when the \f[V]-p\f[R] \f[V]port\f[R] option is
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omitted.
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You can stop the creation of an internal RMI registry by specifying the
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\f[V]-nr\f[R] option.
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.SH OPTIONS FOR THE JSTATD COMMAND
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.TP
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\f[V]-nr\f[R]
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This option does not attempt to create an internal RMI registry within
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the \f[V]jstatd\f[R] process when an existing RMI registry isn\[aq]t
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found.
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.TP
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\f[V]-p\f[R] \f[I]port\f[R]
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This option sets the port number where the RMI registry is expected to
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be found, or when not found, created if the \f[V]-nr\f[R] option
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isn\[aq]t specified.
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.TP
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\f[V]-r\f[R] \f[I]rmiport\f[R]
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This option sets the port number to which the RMI connector is bound.
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If not specified a random available port is used.
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.TP
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\f[V]-n\f[R] \f[I]rminame\f[R]
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This option sets the name to which the remote RMI object is bound in the
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RMI registry.
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The default name is \f[V]JStatRemoteHost\f[R].
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If multiple \f[V]jstatd\f[R] servers are started on the same host, then
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the name of the exported RMI object for each server can be made unique
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by specifying this option.
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However, doing so requires that the unique server name be included in
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the monitoring client\[aq]s \f[V]hostid\f[R] and \f[V]vmid\f[R] strings.
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.TP
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\f[V]-J\f[R]\f[I]option\f[R]
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This option passes a Java \f[V]option\f[R] to the JVM, where the option
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is one of those described on the reference page for the Java application
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launcher.
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For example, \f[V]-J-Xms48m\f[R] sets the startup memory to 48 MB.
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See \f[B]java\f[R].
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.SH SECURITY
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.PP
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The \f[V]jstatd\f[R] server can monitor only JVMs for which it has the
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appropriate native access permissions.
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Therefore, the \f[V]jstatd\f[R] process must be running with the same
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user credentials as the target JVMs.
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Some user credentials, such as the root user in Linux and macOS
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operating systems, have permission to access the instrumentation
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exported by any JVM on the system.
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A \f[V]jstatd\f[R] process running with such credentials can monitor any
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JVM on the system, but introduces additional security concerns.
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.PP
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The \f[V]jstatd\f[R] server doesn\[aq]t provide any authentication of
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remote clients.
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Therefore, running a \f[V]jstatd\f[R] server process exposes the
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instrumentation export by all JVMs for which the \f[V]jstatd\f[R]
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process has access permissions to any user on the network.
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This exposure might be undesirable in your environment, and therefore,
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local security policies should be considered before you start the
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\f[V]jstatd\f[R] process, particularly in production environments or on
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networks that aren\[aq]t secure.
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.PP
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For security purposes, the \f[V]jstatd\f[R] server uses an RMI
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ObjectInputFilter to allow only essential classes to be deserialized.
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.PP
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If your security concerns can\[aq]t be addressed, then the safest action
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is to not run the \f[V]jstatd\f[R] server and use the \f[V]jstat\f[R]
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and \f[V]jps\f[R] tools locally.
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However, when using \f[V]jps\f[R] to get a list of instrumented JVMs,
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the list will not include any JVMs running in docker containers.
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.SH REMOTE INTERFACE
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.PP
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The interface exported by the \f[V]jstatd\f[R] process is proprietary
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and guaranteed to change.
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Users and developers are discouraged from writing to this interface.
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.SH EXAMPLES
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.PP
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The following are examples of the \f[V]jstatd\f[R] command.
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The \f[V]jstatd\f[R] scripts automatically start the server in the
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background.
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.SH INTERNAL RMI REGISTRY
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.PP
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This example shows how to start a \f[V]jstatd\f[R] session with an
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internal RMI registry.
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This example assumes that no other server is bound to the default RMI
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registry port (port \f[V]1099\f[R]).
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.RS
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.PP
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\f[V]jstatd\f[R]
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.RE
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.SH EXTERNAL RMI REGISTRY
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.PP
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This example starts a \f[V]jstatd\f[R] session with an external RMI
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registry.
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.IP
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.nf
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\f[CB]
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rmiregistry&
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jstatd
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\f[R]
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.fi
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.PP
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This example starts a \f[V]jstatd\f[R] session with an external RMI
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registry server on port \f[V]2020\f[R].
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.IP
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.nf
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\f[CB]
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jrmiregistry 2020&
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jstatd -p 2020
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\f[R]
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.fi
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.PP
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This example starts a \f[V]jstatd\f[R] session with an external RMI
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registry server on port \f[V]2020\f[R] and JMX connector bound to port
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\f[V]2021\f[R].
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.IP
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.nf
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\f[CB]
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jrmiregistry 2020&
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jstatd -p 2020 -r 2021
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\f[R]
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.fi
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.PP
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This example starts a \f[V]jstatd\f[R] session with an external RMI
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registry on port 2020 that\[aq]s bound to
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\f[V]AlternateJstatdServerName\f[R].
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.IP
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.nf
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\f[CB]
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rmiregistry 2020&
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jstatd -p 2020 -n AlternateJstatdServerName
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\f[R]
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.fi
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.SH STOP THE CREATION OF AN IN-PROCESS RMI REGISTRY
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.PP
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This example starts a \f[V]jstatd\f[R] session that doesn\[aq]t create
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an RMI registry when one isn\[aq]t found.
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This example assumes an RMI registry is already running.
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If an RMI registry isn\[aq]t running, then an error message is
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displayed.
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.RS
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.PP
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\f[V]jstatd -nr\f[R]
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.RE
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.SH ENABLE RMI LOGGING
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.PP
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This example starts a \f[V]jstatd\f[R] session with RMI logging
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capabilities enabled.
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This technique is useful as a troubleshooting aid or for monitoring
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server activities.
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.RS
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.PP
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\f[V]jstatd -J-Djava.rmi.server.logCalls=true\f[R]
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.RE
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