JCMD(1)

📦 version 25.0.5.0.3.u1, in arch rolling

✨ NAME ✨

okay so bestie, this is JCMD(1) — the jcmd page from the JDK Commands manual. jcmd sends diagnostic command requests to a running Java Virtual Machine (JVM). That's the whole assignment, periodt. 💅

🎀 SYNOPSIS 🎀

jcmd [pid | main-class] command...  | PerfCounter.print | -f filename

jcmd [-l]

jcmd -h
  • pid — when you use it, the jcmd utility sends the diagnostic command request to the process ID for the Java process. 🫶
  • main-class — when you use it, the jcmd utility sends the diagnostic command request to all Java processes with the specified name of the main class.
  • command — has to be a valid jcmd command for the selected JVM. You get the list of available commands for jcmd by running the help command (jcmd pid help), where pid is the process ID for the running Java process. ✨
  • Perfcounter.print — prints the performance counters exposed by the specified Java process.
  • -f filename — reads and executes commands from the specified file, filename.
  • -l — displays the list of Java Virtual Machine process identifiers that are not running in a separate docker process, along with the main class and command-line arguments that were used to launch the process. If the JVM is in a docker process, you must use tools such as ps to look up the PID.
  • -h — displays the jcmd utility's command-line help.
Note: using jcmd without arguments is the same as using jcmd -l. 🫡

💖 DESCRIPTION 💖

okay so the tea: the jcmd utility is used to send diagnostic command requests to the JVM. It must be used on the same machine on which the JVM is running, and have the same effective user and group identifiers that were used to launch the JVM. no cap. 🫶

Each diagnostic command has its own set of options and arguments. To display the description, syntax, and a list of available options and arguments for a diagnostic command, use the name of the command as the argument. For example:

jcmd pid help command

If arguments contain spaces, then you must surround them with single or double quotation marks (' or "). In addition, you must escape single or double quotation marks with a backslash (\) to prevent the operating system shell from processing quotation marks. Alternatively, you can surround these arguments with single quotation marks and then with double quotation marks (or with double quotation marks and then with single quotation marks). 😭

If you specify the process identifier (pid) or the main class (main-class) as the first argument, then the jcmd utility sends the diagnostic command request to the Java process with the specified identifier, or to all Java processes with the specified name of the main class. You can also send the diagnostic command request to all available Java processes by specifying 0 as the process identifier. 🔥

🛠️ COMMANDS FOR JCMD 🛠️

The command must be a valid jcmd diagnostic command for the selected JVM. The list of available commands for jcmd is obtained by running the help command (jcmd pid help), where pid is the process ID for a running Java process. If the pid is 0, commands will be sent to all Java processes. The main class argument will be used to match, either partially or fully, the class used to start Java. If no options are given, it lists the running Java process identifiers that are not in separate docker processes, along with the main class and command-line arguments that were used to launch the process (the same as using -l). ✨

jcmd commands may take options and arguments. Options are specified using either key or key=value syntax. Arguments are given as just a value, never name=value. 💅

The following commands are available:

help [options] [arguments]

For more information about a specific command.

arguments:

  • command name — the name of the command for which we want help (STRING, no default value).
Note: the following options must be specified using either key or key=value syntax.

options:

  • -all — (Optional) show help for all commands (BOOLEAN, false).

AOT.end_recording

Ends an in-progress AOT training and records the results to the file(s) specified by -XX:AOTConfiguration and/or -XX:AOTCacheOutput. 🌸

Impact: Low

Note: the JVM must be started in AOT training mode using command-line arguments such as -XX:AOTMode=record or -XX:AOTCacheOutput=<file>. The results of the AOT training can be an AOT configuration file, an AOT cache file, or both.

Compiler.CodeHeap_Analytics [function] [granularity]

Print CodeHeap analytics.

Impact: Low: depends on code heap size and content. Holds CodeCache_lock during analysis step, usually sub-second duration.

arguments:

  • function — (Optional) function to be performed: aggregate, UsedSpace, FreeSpace, MethodCount, MethodSpace, MethodAge, MethodNames, discard (STRING, all).
  • granularity — (Optional) detail level — smaller value -> more detail (INT, 4096).

Compiler.codecache

Prints code cache layout and bounds.

Impact: Low

Compiler.codelist

Prints all compiled methods in code cache that are alive.

Impact: Medium

Compiler.directives_add arguments

Adds compiler directives from a file.

Impact: Low

arguments:

  • filename — the name of the directives file (STRING, no default value).

Compiler.directives_clear

Remove all compiler directives.

Impact: Low

Compiler.directives_print

Prints all active compiler directives.

Impact: Low

Compiler.directives_remove

Remove latest added compiler directive.

Impact: Low

Compiler.memory [options]

Print compilation footprint.

Impact: Medium: pause time depends on number of compiled methods.

Note: the options must be specified using either key or key=value syntax.

options:

  • -H — (Optional) human readable format (BOOLEAN, false).
  • -s — (Optional) minimum memory size (MEMORY SIZE, 0).

Compiler.perfmap [arguments] (Linux only)

Write map file for Linux perf tool.

Impact: Low

arguments:

  • filename — (Optional) the name of the map file. If %p is specified in the filename, it is expanded to the JVM's PID. (FILE, "/tmp/perf-%p.map").

Compiler.queue

Prints methods queued for compilation.

Impact: Low

GC.class_histogram [options]

Provides statistics about the Java heap usage.

Impact: High --- depends on Java heap size and content.

Note: the options must be specified using either key or key=value syntax.

options:

  • -all — (Optional) inspects all objects, including unreachable objects (BOOLEAN, false).
  • -parallel — (Optional) number of parallel threads to use for heap inspection. 0 (the default) means let the VM determine the number of threads to use. 1 means use one thread (disable parallelism). For any other value the VM will try to use the specified number of threads, but might use fewer. (INT, 0).

GC.finalizer_info

Provides information about the Java finalization queue.

Impact: Medium

GC.heap_dump [options] filename

Generates a HPROF format dump of the Java heap.

Impact: High --- depends on the Java heap size and content. Request a full GC unless the -all option is specified.

Note: the following options must be specified using either key or key=value syntax.

options:

  • -all — (Optional) dump all objects, including unreachable objects (BOOLEAN, false).
  • -gz — (Optional) if specified, the heap dump is written in gzipped format using the given compression level. 1 (recommended) is the fastest, 9 the strongest compression. (INT, 1).
  • -overwrite — (Optional) if specified, the dump file will be overwritten if it exists (BOOLEAN, false).
  • -parallel — (Optional) number of parallel threads to use for heap dump. The VM will try to use the specified number of threads, but might use fewer. (INT, 1).

arguments:

  • filename — the name of the dump file. If %p is specified in the filename, it is expanded to the JVM's PID. (FILE, no default value).

GC.heap_info

Provides generic Java heap information.

Impact: Medium

GC.run

Calls java.lang.System.gc().

Impact: Medium --- depends on the Java heap size and content.

GC.run_finalization

Calls java.lang.System.runFinalization().

Impact: Medium --- depends on the Java content.

JFR.check [options]

Show information about a running flight recording.

Impact: Low

Note: the options must be specified using either key or key=value syntax. If no parameters are entered, information for all active recordings is shown.

options:

  • name — (Optional) name of the flight recording. (STRING, no default value).
  • verbose — (Optional) flag for printing the event settings for the recording (BOOLEAN, false).

JFR.configure [options]

Set the parameters for a flight recording.

Impact: Low

Note: the options must be specified using either key or key=value syntax. If no parameters are entered, the current settings are displayed.

options:

  • dumppath — (Optional) path to the location where a recording file is written in case the VM runs into a critical error, such as a system crash. (STRING, the default location is the current directory).
  • globalbuffercount — (Optional) number of global buffers. This option is a legacy option: change the memorysize parameter to alter the number of global buffers. This value cannot be changed once JFR has been initialized. (STRING, default determined by the value for memorysize).
  • globalbuffersize — (Optional) size of the global buffers, in bytes. This option is a legacy option: change the memorysize parameter to alter the size of the global buffers. This value cannot be changed once JFR has been initialized. (STRING, default determined by the value for memorysize).
  • maxchunksize — (Optional) maximum size of an individual data chunk in bytes if one of the following suffixes is not used: 'm' or 'M' for megabytes OR 'g' or 'G' for gigabytes. This value cannot be changed once JFR has been initialized. (STRING, 12M).
  • memorysize — (Optional) the overall memory size, in bytes unless you slap one of these suffixes on it: 'm' or 'M' for megabytes OR 'g' or 'G' for gigabytes. Real talk: you literally cannot change this once JFR has been initialized. (STRING, 10M)
  • repositorypath — (Optional) the path to where recordings get stashed until they're written out to a permanent file. (STRING, default is the temporary directory for the operating system. On Linux operating systems, the temporary directory is /tmp. On Windows, the temporary directory is specified by the TMP environment variable.)
  • preserve-repository={true|false} — says whether files chillin' in the disk repository should be kept after the JVM has exited. If false, the files get deleted. By default? This one is disabled. 🫶
  • stackdepth — (Optional) stack depth for stack traces. Setting this higher than the default of 64 may cause a performance degradation 😭. And no, you can't change it once JFR has been initialized. (LONG, 64)
  • thread_buffer_size — (Optional) the local buffer size for each thread, in bytes unless you use one of these suffixes: 'k' or 'K' for kilobytes or 'm' or 'M' for megabytes. Heads up: overriding this could reduce performance and is not recommended. Cannot be changed once JFR has been initialized either. (STRING, 8k)
  • samplethreads — (Optional) flag for activating thread sampling. (BOOLEAN, true)

💅 JFR.dump [options]

Write data to a file while a flight recording is running. Impact: Low. Note: the options must be specified using either key or key=value syntax. No options are required. The recording keeps running after the data is written — she does not stop, she just shares. Options:

  • begin — (Optional) the time from which recording data will be included in the dump file. The format is specified as local time. (STRING, no default value)
  • end — (Optional) the time to which recording data will be included in the dump file. The format is specified as local time. (STRING, no default value)
Note: for both begin and end, the time must be in a format that can be read by java.time.LocalTime::parse(STRING), java.time.LocalDateTime::parse(STRING) or java.time.Instant::parse(STRING). For example, "13:20:15", "2020-03-17T09:00:00" or "2020-03-17T09:00:00Z".
Note: begin and end times correspond to the timestamps found within the recorded information in the flight recording data.

Another option is to use a time relative to the current time that is specified by a negative integer followed by "s", "m" or "h". For example, "-12h", "-15m" or "-30s" ✨

  • filename — (Optional) name of the file to which the flight recording data is dumped. If no filename is given, a filename is generated from the PID and the current date. The filename may also be a directory, in which case the filename is generated from the PID and the current date in the specified directory. If %p and/or %t is specified in the filename, it expands to the JVM's PID and the current timestamp, respectively. (FILE, no default value)
  • maxage — (Optional) length of time for dumping the flight recording data to a file. (INTEGER followed by 's' for seconds 'm' for minutes or 'h' for hours, no default value)
  • maxsize — (Optional) maximum size for the amount of data to dump from a flight recording, in bytes unless one of the following suffixes is used: 'm' or 'M' for megabytes OR 'g' or 'G' for gigabytes. (STRING, no default value)
  • name — (Optional) name of the recording. If no name is given, data from all recordings is dumped. (STRING, no default value)
  • path-to-gc-roots — (Optional) flag for saving the path to garbage collection (GC) roots at the time the recording data is dumped. This path info is useful for finding memory leaks, but collecting it can cause the application to pause for a short period of time 😬. Turn on this flag only when you have an application that you suspect has a memory leak. (BOOLEAN, false)

🦋 JFR.start [options]

Start a flight recording. Impact: Low. Note: the options must be specified using either key or key=value syntax. If no parameters are entered, then a recording is started with default values. Options:

  • delay — (Optional) length of time to wait before starting to record. (INTEGER followed by 's' for seconds 'm' for minutes or 'h' for hours, 0s)
  • disk — (Optional) flag for also writing the data to disk while recording. (BOOLEAN, true)
  • dumponexit — (Optional) flag for writing the recording to disk when the Java Virtual Machine (JVM) shuts down. If set to 'true' and no value is given for filename, the recording is written to a file in the directory where the process was started. The file name is a system-generated name that contains the process ID, the recording ID and the current time stamp. (For example: id-1-2019_12_12_10_41.jfr) (BOOLEAN, false)
  • duration — (Optional) length of time to record. Note that 0s means forever 👑 (INTEGER followed by 's' for seconds 'm' for minutes or 'h' for hours, 0s)
  • filename — (Optional) name of the file to which the flight recording data is written when the recording is stopped. If no filename is given, a filename is generated from the PID and the current date and is placed in the directory where the process was started. The filename may also be a directory, in which case the filename is generated from the PID and the current date in the specified directory. If %p and/or %t is specified in the filename, it expands to the JVM's PID and the current timestamp, respectively. (FILE, no default value)
  • maxage — (Optional) maximum time to keep the recorded data on disk. This parameter is valid only when the disk parameter is set to true. Note 0s means forever. (INTEGER followed by 's' for seconds 'm' for minutes or 'h' for hours, 0s)
  • maxsize — (Optional) maximum size of the data to keep on disk, in bytes unless one of the following suffixes is used: 'm' or 'M' for megabytes OR 'g' or 'G' for gigabytes. This parameter is valid only when the disk parameter is set to 'true'. The value must not be less than the value for the maxchunksize parameter set with the JFR.configure command. (STRING, 0 (no maximum size))
  • name — (Optional) name of the recording. If no name is provided, a name is generated. Make note of the generated name that is shown in the response to the command so that you can use it with other commands — iykyk, write it down bestie 📝 (STRING, system-generated default name)
  • path-to-gc-roots — (Optional) flag for saving the path to garbage collection (GC) roots at the end of a recording. The path information is useful for finding memory leaks but collecting it is time consuming. Turn on this flag only when you have an application that you suspect has a memory leak. If the settings parameter is set to 'profile', then the information collected includes the stack trace from where the potential leaking object was allocated. (BOOLEAN, false)
  • settings — (Optional) name of the settings file that identifies which events to record. To specify more than one file, separate the names with a comma (','). Include the path if the file is not in JAVA-HOME/lib/jfr. The following profiles are included with the JDK in the JAVA-HOME/lib/jfr directory: 'default.jfc' collects a predefined set of information with low overhead, so it has minimal impact on performance and can be used with recordings that run continuously; 'profile.jfc' provides more data than the 'default.jfc' profile, but with more overhead and impact on performance — use this configuration for short periods of time when more information is needed. Use none to start a recording without a predefined configuration file. (STRING, JAVA-HOME/lib/jfr/default.jfc) Event settings and .jfc options can be specified using the following syntax:
    • option — (Optional) specifies the option value to modify. To list available options, use the JAVA_HOME/bin/jfr tool.
    • event-setting — (Optional) specifies the event setting value to modify. Use the form: <event-name>#<setting-name>=<value> To add a new event setting, prefix the event name with '+'. You can specify values for multiple event settings and .jfc options by separating them with a whitespace. In case of a conflict between a parameter and a .jfc option, the parameter will take precedence. The whitespace delimiter can be omitted for timespan values, i.e. 20ms. For more information about the settings syntax, see Javadoc of the jdk.jfr package.

🎀 JFR.stop [options]

Stop a flight recording. Impact: Low. Note: the options must be specified using either key or key=value syntax. If no parameters are entered, then no recording is stopped. Options:

  • filename — (Optional) name of the file to which the recording is written when the recording is stopped. If %p and/or %t is specified in the filename, it expands to the JVM's PID and the current timestamp, respectively. If no path is provided, the data from the recording is discarded 💀 (FILE, no default value)
  • name — (Optional) name of the recording. (STRING, no default value)

🌈 JFR.view [options]

Display event data in predefined views. Impact: Medium. Note: the options must be specified using either key or key=value syntax. If no parameters are entered, then a list of available views are displayed — free tour, no cap ✨ Options:

  • cell-height — (Optional) maximum number of rows in a table cell. (INT, default value depends on the view)
  • maxage — (Optional) how long the view spans. It's an INT followed by s for seconds, m for minutes or h for hours, and the default is 10m. ⏱️
    • maxsize — (Optional) the max size the view can span, in bytes — unless you use one of the suffixes: m or M for megabytes, or g or G for gigabytes. (STRING, default is 32MB) 📦
    • truncate — (Optional) the max number of rows in a table cell. (INT, default depends on the view) ✂️
    • verbose — (Optional) shows you the query that makes up the view. (BOOLEAN, default false) 👀
    • width — (Optional) the width of the view in characters. (INT, default depends on the view) 📏

arguments:

  • view — the name of the view or event type to display. Run help JFR.view to see the list of available views. (STRING, no default value) The view parameter can also be an event type name — use JFR.view types to see a list of those. Wanna see literally everything? JFR.view all-views for all views, JFR.view all-events for all events. 🦋

JVMTI.agent_load [arguments]

Loads a JVMTI native agent. 🧚

Impact: Low

arguments:

  • library path — the absolute path of the JVMTI agent to load. (STRING, no default value) 📂
  • agent option — (Optional) an option string to pass along to the agent. (STRING, no default value) 💌

JVMTI.data_dump

Signals the JVM to do a data-dump request for JVMTI. 📸

Impact: High 🔥

ManagementAgent.start [options]

Starts the remote management agent. 👑

Impact: Low --- no impact

Note: the following options must be specified using either key or key=value syntax.

options:

  • config.file — (Optional) sets com.sun.management.config.file (STRING, no default value)
  • jmxremote.host — (Optional) sets com.sun.management.jmxremote.host (STRING, no default value)
  • jmxremote.port — (Optional) sets com.sun.management.jmxremote.port (STRING, no default value)
  • jmxremote.rmi.port — (Optional) sets com.sun.management.jmxremote.rmi.port (STRING, no default value)
  • jmxremote.ssl — (Optional) sets com.sun.management.jmxremote.ssl (STRING, no default value)
  • jmxremote.registry.ssl — (Optional) sets com.sun.management.jmxremote.registry.ssl (STRING, no default value)
  • jmxremote.authenticate — (Optional) sets com.sun.management.jmxremote.authenticate (STRING, no default value)
  • jmxremote.password.file — (Optional) sets com.sun.management.jmxremote.password.file (STRING, no default value)
  • jmxremote.access.file — (Optional) sets com.sun.management.jmxremote.access.file (STRING, no default value)
  • jmxremote.login.config — (Optional) sets com.sun.management.jmxremote.login.config (STRING, no default value)
  • jmxremote.ssl.enabled.cipher.suites — (Optional) sets com.sun.management.
  • jmxremote.ssl.enabled.cipher.suite — (STRING, no default value)
  • jmxremote.ssl.enabled.protocols — (Optional) sets com.sun.management.jmxremote.ssl.enabled.protocols (STRING, no default value)
  • jmxremote.ssl.need.client.auth — (Optional) sets com.sun.management.jmxremote.need.client.auth (STRING, no default value)
  • jmxremote.ssl.config.file — (Optional) sets com.sun.management.jmxremote.ssl_config_file (STRING, no default value)
  • jmxremote.autodiscovery — (Optional) sets com.sun.management.jmxremote.autodiscovery (STRING, no default value)
  • jdp.port — (Optional) sets com.sun.management.jdp.port (INT, no default value)
  • jdp.address — (Optional) sets com.sun.management.jdp.address (STRING, no default value)
  • jdp.source_addr — (Optional) sets com.sun.management.jdp.source_addr (STRING, no default value)
  • jdp.ttl — (Optional) sets com.sun.management.jdp.ttl (INT, no default value)
  • jdp.pause — (Optional) sets com.sun.management.jdp.pause (INT, no default value)
  • jdp.name — (Optional) sets com.sun.management.jdp.name (STRING, no default value)

ManagementAgent.start_local

Starts the local management agent. 🏠

Impact: Low --- no impact

ManagementAgent.status

Prints the management agent status. 📋

Impact: Low --- no impact

ManagementAgent.stop

Stops the remote management agent. 🛑

Impact: Low --- no impact

System.dump_map [options] (Linux only) 🐧

Dumps an annotated process memory map to an output file.

Impact: Low

Note: the following options must be specified using either key or key=value syntax.

options:

  • -H — (Optional) human readable format (BOOLEAN, false)
  • -F — (Optional) file path. If %p shows up in the filename, it gets expanded to the JVM's PID. (FILE, "vm_memory_map_%p.txt")

System.map [options] (Linux only) 🐧

Prints an annotated process memory map of the VM process.

Impact: Low

Note: the following options must be specified using either key or key=value syntax.

options:

  • -H — (Optional) human readable format (BOOLEAN, false)

System.native_heap_info (Linux only) 🐧

Attempts to output info about native heap usage via malloc_info(3). If it can't, it outputs "Error: " plus a reason. 😭

Impact: Low

System.trim_native_heap (Linux only) 🐧

Attempts to free up memory by trimming the C-heap. 🧹✨

Impact: Low

Thread.dump_to_file [options] filepath

Dumps threads, with stack traces, to a file — either plain text or JSON. 🧵💾

Impact: Medium: depends on the number of threads.

Note: the following options must be specified using either key or key=value syntax.

options:

  • -overwrite — (Optional) may overwrite an existing file (BOOLEAN, false)
  • -format — (Optional) output format ("plain" or "json") (STRING, plain)

arguments:

  • filepath — the file path to the output file. If %p shows up in the filename, it gets expanded to the JVM's PID. (FILE, no default value)

Thread.print [options]

Prints all the threads, with stacktraces. 🖨️🧵

Impact: Medium --- depends on the number of threads.

Note: the following options must be specified using either key or key=value syntax.

options:

  • -e — (Optional) print extended thread information (BOOLEAN, false)
  • -l — (Optional) prints java.util.concurrent locks (BOOLEAN, false)

Thread.vthread_scheduler

Prints the virtual thread scheduler — plus the delayed task schedulers that support virtual threads doing timed operations. ⏰🦋

Impact: Low

Thread.vthread_pollers

Prints the I/O pollers that support virtual threads doing blocking network I/O operations. 🌐

Impact: Low

VM.cds [arguments]

Dumps a static or dynamic shared archive that includes all currently loaded classes. 🗄️

Impact: Medium --- pause time depends on number of loaded classes

arguments:

  • subcmd — must be either static_dump or dynamic_dump (STRING, no default value)
  • filename — (Optional) name of the shared archive to be dumped. If %p shows up in the filename, it gets expanded to the JVM's PID. (FILE, "java_pid%p_<subcmd>.jsa")
Heads up bestie: if dynamic_dump is specified, the target JVM must be started with the JVM option -XX:+RecordDynamicDumpInfo. No cap, it won't work otherwise. 💅

VM.class_hierarchy [options] [arguments]

Prints a list of all loaded classes, indented so you can actually see the class hierarchy. 🌳 The name of each class is followed by the ClassLoaderData* of its ClassLoader, or "null" if it's loaded by the bootstrap class loader.

Impact: Medium --- depends on the number of loaded classes.

Note: the following options must be specified using either key or key=value syntax.

options:

  • -i — (Optional) inherited interfaces should be printed. (BOOLEAN, false)
  • -s — (Optional) if a classname is specified, print its subclasses in addition to its superclasses. Without this option only the superclasses get printed. (BOOLEAN, false)

arguments:

  • classname — (Optional) the name of the class whose hierarchy should be printed. If you don't specify it, all class hierarchies get printed. (STRING, no default value)

VM.classes [options]

Prints all loaded classes. 🗂️

Impact: Medium: depends on number of loaded classes.

The following options must be specified using either key or key=value syntax.

options:

  • -verbose — (Optional) dumps the detailed content of a Java class. Some classes get annotated with flags: F = has, or inherits, a non-empty finalize method, f = has final method, W = methods rewritten, C = marked with @Contended annotation, R = has been redefined, S = is shared class (BOOLEAN, false) 🏷️

VM.classloader_stats

Prints statistics about all the ClassLoaders. 📊

Impact: Low

VM.classloaders [options]

Prints the classloader hierarchy. 🪆

Impact: Medium --- depends on number of class loaders and classes loaded.

The following options must be specified using either key or key=value syntax.

options:

  • show-classes — (Optional) print loaded classes. (BOOLEAN, false)
  • verbose — (Optional) print detailed information. (BOOLEAN, false)
  • fold — (Optional) show loaders of the same name and class as one. (BOOLEAN, true)

VM.command_line

Prints the command line used to start this VM instance. 🚀

Impact: Low

VM.dynlibs

Prints loaded dynamic libraries. 📚

Impact: Low

VM.events [options]

Prints VM event logs. 📝

Impact: Low --- depends on event log size.

options: note that the following options must be specified using either key or key=value syntax.
  • log — (Optional) name of the log to be printed. If you omit it, all logs get printed. (STRING, no default value)
  • max — (optional) how many events you actually want, newest ones first. Leave it out or pass zero and you get literally all of them, no cap. (INT, 0)

🌸 VM.flags [options]

Prints the VM flag options and what they're currently set to ✨

Impact: Low

Note, bestie: the following options must be specified using either key or key=value syntax. That's the whole vibe, don't fight it.

Options:

  • -all — (optional) prints every single flag the VM supports, not just the ones you asked about (BOOLEAN, false).

💜 VM.info

Prints info about the JVM environment and its status. It's giving "who am I, where am I, how am I doing" 💅

Impact: Low

🦋 VM.log [options]

Lists your current log configuration, enables/disables/configures a log output, or rotates all the logs. Basically the whole log glow-up station 🎀

Impact: Low

Options:

Note: the following options must be specified using either key or key=value syntax. Yes, again. It's a whole thing.
  • output — (optional) the name or index (#) of the output you want to configure. (STRING, no default value)
  • output_options — (optional) options for that output. (STRING, no default value)
  • what — (optional) configures which tags to log. (STRING, no default value)
  • decorators — (optional) configures which decorators to use. Pass 'none' or an empty value to remove them all. (STRING, no default value)
  • disable — (optional) turns off all logging and clears the log configuration. (BOOLEAN, no default value)
  • list — (optional) lists the current log configuration. (BOOLEAN, no default value)
  • rotate — (optional) rotates all the logs. (BOOLEAN, no default value)

🧚 VM.metaspace [options]

Prints the statistics for the metaspace 🌈

Impact: Medium --- depends on the number of classes loaded.

Note: the following options must be specified using either key or key=value syntax.

Options:

  • basic — (optional) prints a basic summary (does not need a safepoint, so it's the chill low-effort one). (BOOLEAN, false)
  • show-loaders — (optional) shows usage broken down by class loader. (BOOLEAN, false)
  • show-classes — (optional) if show-loaders is set, shows the loaded classes for each loader. (BOOLEAN, false)
  • by-chunktype — (optional) breaks the numbers down by chunk type. (BOOLEAN, false)
  • by-spacetype — (optional) breaks the numbers down by loader type. (BOOLEAN, false)
  • vslist — (optional) shows details about the underlying virtual space. (BOOLEAN, false)
  • chunkfreelist — (optional) shows details about the global chunk free lists (ChunkManager). (BOOLEAN, false)
  • scale — (optional) the scale to express memory usage in. Valid values are 1, KB, MB or GB (fixed scale), or "dynamic" for a dynamically chosen scale. (STRING, dynamic)

🍓 VM.native_memory [options]

Prints native memory usage 🔥

Impact: Medium

Note: the following options must be specified using either key or key=value syntax.

Options:

  • summary — (optional) asks the runtime to report the current memory summary, which includes total reserved and committed memory plus a usage summary for each subsystem. (BOOLEAN, false)
  • detail — (optional) asks the runtime to report memory allocation >= 1K by each callsite. (BOOLEAN, false)
  • baseline — (optional) asks the runtime to baseline the current memory usage, so you can compare against it later. Snapshot time 📸 (BOOLEAN, false)
  • summary.diff — (optional) asks the runtime to report the memory summary compared against the previous baseline. (BOOLEAN, false)
  • detail.diff — (optional) asks the runtime to report the memory detail compared against the previous baseline, which shows the memory allocation activities at different callsites. (BOOLEAN, false)
  • statistics — (optional) prints tracker statistics for tuning purposes. (BOOLEAN, false)
  • scale — (optional) the scale for memory usage: KB, MB or GB. (STRING, KB)

⭐ VM.set_flag [arguments]

Sets a VM flag option to the value you give it 👑

Impact: Low

Arguments:

  • flag name — the name of the flag you want to set. (STRING, no default value)
  • string value — (optional) the value you want to set it to. (STRING, no default value)

💖 VM.stringtable [options]

Dumps the string table.

Impact: Medium --- depends on the Java content.

Note: the following options must be specified using either key or key=value syntax.

Options:

  • -verbose — (optional) dumps the content of each string in the table. (BOOLEAN, false)

🎀 VM.symboltable [options]

Dumps the symbol table.

Impact: Medium --- depends on the Java content.

Note: the following options must be specified using either key or key=value syntax.

Options:

  • -verbose — (optional) dumps the content of each symbol in the table. (BOOLEAN, false)

🌈 VM.system_properties

Prints system properties. Short and sweet 🫶

Impact: Low

👑 VM.systemdictionary

Prints the statistics for dictionary hashtable sizes and bucket length.

Impact: Medium

Note: the following options must be specified using either key or key=value syntax.

Options:

  • verbose — (optional) dumps the content of each dictionary entry for all class loaders. (BOOLEAN, false)

🦋 VM.uptime [options]

Prints the VM uptime. How long has this baby been running ⏱️

Impact: Low

Note: the following options must be specified using either key or key=value syntax.

Options:

  • -date — (optional) adds a prefix with the current date. (BOOLEAN, false)

✨ VM.version

Prints the JVM version information. The classic "what are you" check 💅

Impact: Low

And that's the whole page, bestie — you made it to the end, iconic behavior fr fr 🎉 This glorious little doc is served up by JDK 25.0.5.0.3, dated 2026, and it lives its life as JCMD(1). Go forth and jcmd responsibly 💜🌸

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