jcmd :在哪里可以找到补充信息？

Question

jcmd是重组jmap、jsp等实用工具的一种很有前途的工具。

你可以找到引言和手册页，但仍然很轻。

在网络上，我发现了明显存在的命令，如GC.heap_info，这些命令我从未能够用于我的测试。

其中一些命令需要特殊的标志。例如，-XX:NativeMemoryTracking=detail将为您提供VM.native_memory命令。

但对其他一些人来说，不清楚如何激活它们，或者它是否依赖于jdk版本，等等。

我甚至找不到现有命令的详尽列表。

有什么消息吗？

编辑Thx到@apangin答复，我已经开始根据jvm版本计算可用命令的简短摘要。

免责声明:它只来自代码拆卸，而不是真正的测试。

jdk8

• 帮助
• VM.uptime选项
• VM.flags选项
• VM.system_properties
• VM.command_line
• VM.version
• VM.native_memory选项
• VM.check_commercial_features
• VM.unlock_commercial_features
• Thread.print选项
• GC.run
• GC.run_finalization
• GC.rotate_log
• GC.class_stats选项
• GC.class_histogram选项
• GC.heap_dump选项
• ManagementAgent.start_local
• ManagementAgent.start选项
• ManagementAgent.stopJFR.start选项
• JFR.stop选项
• JFR.dump选项
• JFR.check选项

jdk9

仅为附加的

• VM.set_flag选项
• VM.info
• VM.class_hierarchy选项
• VM.dynlibs
• VM.print_touched_methods
• JVMTI.data_dump
• JVMTI.agent_load选项
• GC.finalizer_info
• GC.heap_info
• ManagementAgent.status
• ManagementAgent.stop
• Compiler.queue
• Compiler.codelist
• Compiler.codecache
• Compiler.directives_print
• Compiler.directives_remove
• Compiler.directives_add选项
• Compiler.directives_clear

Answer 1

基于@EricWang的回答、HotSpot诊断命令源和个人经验，我创建了JDK8u121中可用的jcmd命令的完整列表，并提供了有关需求等的其他详细信息。

帮助选项

有关特定命令的更多信息，请使用help <command>。在没有参数的情况下，这将显示可用命令的列表。help -all将显示所有命令的帮助。

• 影响:低

Arguments:
    command name : [optional] The name of the command for which we want help (STRING, no default value)

Options: (options must be specified using the <key> or <key>=<value> syntax)
    -all : [optional] Show help for all commands (BOOLEAN, false)

VM.uptime选项

打印VM正常运行时间。

• 影响:低

Options: (options must be specified using the <key> or <key>=<value> syntax)
    -date : [optional] Add a prefix with current date (BOOLEAN, false)

VM.flags选项

打印VM标志选项及其当前值。

• 影响:低

Options: (options must be specified using the <key> or <key>=<value> syntax)
    -all : [optional] Print all flags supported by the VM (BOOLEAN, false)

VM.system_properties

打印系统属性。

• 影响:低

VM.command_line

打印用于启动此VM实例的命令行。

• 影响:低

VM.version

打印JVM版本信息。

• 影响:低

VM.native_memory选项

打印本机内存使用情况。

• 影响:中等
• 要求：-XX:NativeMemoryTracking=[summary|detail]

Options: (options must be specified using the <key> or <key>=<value> syntax)
    summary : [optional] request runtime to report current memory summary, which includes total reserved and committed memory, along with memory usage summary by each subsytem. (BOOLEAN, false)
    detail : [optional] request runtime to report memory allocation >= 1K by each callsite. (BOOLEAN, false)
    baseline : [optional] request runtime to baseline current memory usage, so it can be compared against in later time. (BOOLEAN, false)
    summary.diff : [optional] request runtime to report memory summary comparison against previous baseline. (BOOLEAN, false)
    detail.diff : [optional] request runtime to report memory detail comparison against previous baseline, which shows the memory allocation activities at different callsites. (BOOLEAN, false)
    shutdown : [optional] request runtime to shutdown itself and free the memory used by runtime. (BOOLEAN, false)
    statistics : [optional] print tracker statistics for tuning purpose. (BOOLEAN, false)
    scale : [optional] Memory usage in which scale, KB, MB or GB (STRING, KB)

VM.check_commercial_features

显示商业功能的状态。

• 影响:低:无影响

VM.unlock_commercial_features

解锁商业功能。

• 影响:低:无影响

Thread.print选项

打印所有具有堆栈痕迹的线程。

• 影响:中介:取决于线程的数量。

Options: (options must be specified using the <key> or <key>=<value> syntax)
    -l : [optional] print java.util.concurrent locks (BOOLEAN, false)

GC.run

调用java.lang.System.gc()。

• 影响: Medium:取决于Java堆的大小和内容。

GC.run_finalization

调用java.lang.System.runFinalization()。

• 影响: Medium:取决于Java内容。

GC.rotate_log

强制旋转GC日志文件。

• 影响:低
• 要求：-Xloggc:<filename> -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=<num>

GC.class_stats选项

提供有关Java类元数据的统计信息。

• 影响:高:取决于Java堆的大小和内容。
• 要求：-XX:+UnlockDiagnosticVMOptions

Arguments:
    columns : [optional] Comma-separated list of all the columns to show. If not specified, the following columns are shown: InstBytes,KlassBytes,CpAll,annotations,MethodCount,Bytecodes,MethodAll,ROAll,RWAll,Total (STRING, no default value)

Options: (options must be specified using the <key> or <key>=<value> syntax)
    -all : [optional] Show all columns (BOOLEAN, false)
    -csv : [optional] Print in CSV (comma-separated values) format for spreadsheets (BOOLEAN, false)
    -help : [optional] Show meaning of all the columns (BOOLEAN, false)

GC.class_histogram选项

提供有关Java堆使用情况的统计信息。

• 影响:高:取决于Java堆的大小和内容。

Options: (options must be specified using the <key> or <key>=<value> syntax)
    -all : [optional] Inspect all objects, including unreachable objects (BOOLEAN, false)

GC.heap_dump选项

生成Java堆的HPROF格式转储。

• 影响:高:取决于Java堆的大小和内容。除非指定了-all选项，否则请求完整的GC。

Arguments:
    filename : Name of the dump file (STRING, no default value)

Options: (options must be specified using the <key> or <key>=<value> syntax)
    -all : [optional] Dump all objects, including unreachable objects (BOOLEAN, false)

ManagementAgent.start_local

启动本地管理代理。

• 影响:低:无影响

ManagementAgent.start选项

启动远程管理代理。

• 影响:低:无影响

Options: (options must be specified using the <key> or <key>=<value> syntax)
    config.file : [optional] set com.sun.management.config.file (STRING, no default value)
    jmxremote.host : [optional] set com.sun.management.jmxremote.host (STRING, no default value)
    jmxremote.port : [optional] set com.sun.management.jmxremote.port (STRING, no default value)
    jmxremote.rmi.port : [optional] set com.sun.management.jmxremote.rmi.port (STRING, no default value)
    jmxremote.ssl : [optional] set com.sun.management.jmxremote.ssl (STRING, no default value)
    jmxremote.registry.ssl : [optional] set com.sun.management.jmxremote.registry.ssl (STRING, no default value)
    jmxremote.authenticate : [optional] set com.sun.management.jmxremote.authenticate (STRING, no default value)
    jmxremote.password.file : [optional] set com.sun.management.jmxremote.password.file (STRING, no default value)
    jmxremote.access.file : [optional] set com.sun.management.jmxremote.access.file (STRING, no default value)
    jmxremote.login.config : [optional] set com.sun.management.jmxremote.login.config (STRING, no default value)
    jmxremote.ssl.enabled.cipher.suites : [optional] set com.sun.management.jmxremote.ssl.enabled.cipher.suite (STRING, no default value)
    jmxremote.ssl.enabled.protocols : [optional] set com.sun.management.jmxremote.ssl.enabled.protocols (STRING, no default value)
    jmxremote.ssl.need.client.auth : [optional] set com.sun.management.jmxremote.need.client.auth (STRING, no default value)
    jmxremote.ssl.config.file : [optional] set com.sun.management.jmxremote.ssl_config_file (STRING, no default value)
    jmxremote.autodiscovery : [optional] set com.sun.management.jmxremote.autodiscovery (STRING, no default value)
    jdp.port : [optional] set com.sun.management.jdp.port (INT, no default value)
    jdp.address : [optional] set com.sun.management.jdp.address (STRING, no default value)
    jdp.source_addr : [optional] set com.sun.management.jdp.source_addr (STRING, no default value)
    jdp.ttl : [optional] set com.sun.management.jdp.ttl (INT, no default value)
    jdp.pause : [optional] set com.sun.management.jdp.pause (INT, no default value)
    jdp.name : [optional] set com.sun.management.jdp.name (STRING, no default value)

ManagementAgent.stop

停止远程管理代理。

• 影响:低:无影响

JFR.start选项

启动新的JFR录音

• 影响:中等:取决于录制的设置，影响范围从低到高。
• 要求：-XX:+UnlockCommercialFeatures

Options: (options must be specified using the <key> or <key>=<value> syntax)
    name : [optional] Name that can be used to identify recording, e.g. "My Recording" (STRING, no default value)
    defaultrecording : [optional] Starts the default recording, can only be combined with settings. (BOOLEAN, false)
    dumponexit : [optional] Dump running recording when JVM shuts down (BOOLEAN, no default value)
    settings : [optional] Settings file(s), e.g. profile or default. See JRE_HOME/lib/jfr (STRING SET, no default value)
    delay : [optional] Delay recording start with (s)econds, (m)inutes), (h)ours), or (d)ays, e.g. 5h. (NANOTIME, 0)
    duration : [optional] Duration of recording in (s)econds, (m)inutes, (h)ours, or (d)ays, e.g. 300s. (NANOTIME, 0)
    filename : [optional] Resulting recording filename, e.g. "C:\Users\user\My Recording.jfr" (STRING, no default value)
    compress : [optional] GZip-compress the resulting recording file (BOOLEAN, false)
    maxage : [optional] Maximum time to keep recorded data (on disk) in (s)econds, (m)inutes, (h)ours, or (d)ays, e.g. 60m, or 0 for no limit (NANOTIME, 0)
    maxsize : [optional] Maximum amount of bytes to keep (on disk) in (k)B, (M)B or (G)B, e.g. 500M, or 0 for no limit (MEMORY SIZE, 0)

JFR.stop选项

停止JFR录音

• 影响:低
• 要求：-XX:+UnlockCommercialFeatures

Options: (options must be specified using the <key> or <key>=<value> syntax)
    name : [optional] Recording name,.e.g "My Recording" (STRING, no default value)
    recording : [optional] Recording number, see JFR.check for a list of available recordings (JLONG, -1)
    discard : [optional] Skip writing data to previously specified file (if any) (BOOLEAN, false)
    filename : [optional] Copy recording data to file, e.g. "C:\Users\user\My Recording.jfr" (STRING, no default value)
    compress : [optional] GZip-compress "filename" destination (BOOLEAN, false)

JFR.dump选项

将JFR记录的内容复制到文件中。必须指定名称或记录id。

• 影响:低
• 要求：-XX:+UnlockCommercialFeatures

Options: (options must be specified using the <key> or <key>=<value> syntax)
    name : [optional] Recording name, e.g. "My Recording" (STRING, no default value)
    recording : [optional] Recording number, use JFR.check to list available recordings (JLONG, -1)
    filename :  Copy recording data to file, i.e "C:\Users\user\My Recording.jfr" (STRING, no default value)
    compress : [optional] GZip-compress "filename" destination (BOOLEAN, false)

JFR.check选项

运行JFR记录的检查

• 影响:低
• 要求：-XX:+UnlockCommercialFeatures

Options: (options must be specified using the <key> or <key>=<value> syntax)
    name : [optional] Recording name, e.g. "My Recording" or omit to see all recordings (STRING, no default value)
    recording : [optional] Recording number, or omit to see all recordings (JLONG, -1)
    verbose : [optional] Print event settings for the recording(s) (BOOLEAN, false)

Answer 2

jcmd本身在应用于特定的Java时提供这样的信息，并且可以选择一个特定的子命令。

如何获得帮助：

• 首先，通过jps或jcmd -l获取java进程列表，如果您还不知道目标java进程的pid，(例如，在后续步骤中，我将以pid 8976作为示例)。
• 然后将help子命令应用于特定的java进程，例如jcmd 8976 help，它将列出该进程的可用子命令。
• 然后，获取有关进程的特定命令的帮助，例如jcmd 8976 help Thread.print，它将打印Thread.print子命令的帮助。
• 然后，在进程上执行特定的子命令，例如jcmd 8976 Thread.print或jcmd 8976 Thread.print | less -N

顺便提一下，正如您所提到的，下面的链接简要地描述了jcmd命令：https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/tooldescr006.html