jcmd——多功能命令行

「爱情、让人受尽委屈。」 2022-09-07 09:53 314阅读 0赞

# 一 点睛 #

在 JDK 1.7 以后，新增了一个命令行工具 jcmd。它是一个多功能的工具，可以用来实现前面除了 jstat 之外所有命令的功能。比如：用它来导出堆、内存使用、查看 Java 进程、导出线程信息、执行 GC、JVM 运行时间等。

官方帮助文档：[https://docs.oracle.com/en/java/javase/11/tools/jcmd.html][https_docs.oracle.com_en_java_javase_11_tools_jcmd.html]

jcmd 拥有 jmap 的大部分功能，并且在 Oracle 的官方网站上也推荐使用 jcmd 命令代 jmap 命令

jcmd -l：列出所有的 JVM 进程

jcmd 进程号 help：针对指定的进程，列出支持的所有具体命令

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

jcmd 进程号 具体命令：显示指定进程的指令命令的数据

*  Thread.print 可以替换 jstack 指令
 *  GC.class\_histogram 可以替换 jmap 中的-histo 操作
 *  GC.heap\_dump 可以替换 jmap 中的-dump 操作
 *  GC.run 可以查看 GC 的执行情况
 *  VM.uptime 可以查看程序的总执行时间，可以替换 jstat 指令中的 -t 操作
 *  VM.system\_properties 可以替换 jinfo -sysprops 进程 id
 *  VM.flags 可以获取 JVM 的配置参数信息

# 二 实战 #

## 1 基本使用 ##

# jcmd 单独使用功能类似 jps
    E:\JVMDemo3>jcmd
    10576
    4444 sun.tools.jcmd.JCmd
    
    E:\JVMDemo3>jps
    10576
    4556 Jps
    
    # jcmd 的帮助
    E:\JVMDemo3>jcmd -h
    Usage: jcmd <pid | main class> <command ...|PerfCounter.print|-f file>
       or: jcmd -l
       or: jcmd -h
    
      command must be a valid jcmd command for the selected jvm.
      Use the command "help" to see which commands are available.
      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, lists Java processes (same as -p).
    
      PerfCounter.print display the counters exposed by this process
      -f  read and execute commands from the file
      -l  list JVM processes on the local machine
      -h  this help

## 2 jcmd -l——类似 jps 功能 ##

E:\JVMDemo3>jcmd -l
    10576
    13716 sun.tools.jcmd.JCmd -l
    16324 org.jetbrains.jps.cmdline.Launcher D:/ProgramFiles/JetBrains/IDEA/lib/jna.jar;D:/ProgramFiles/JetBrains/IDEA/lib/maven-builder-support-3.6.1.jar;D:/ProgramFiles/JetBrains/IDEA/lib/httpclient-4.5.12.jar;D:/ProgramFiles/JetBrain
    s/IDEA/lib/slf4j-api-1.7.25.jar;D:/ProgramFiles/JetBrains/IDEA/plugins/java/lib/jps-builders.jar;D:/ProgramFiles/JetBrains/IDEA/lib/maven-resolver-provider-3.6.1.jar;D:/ProgramFiles/JetBrains/IDEA/lib/lz4-java-1.7.1.jar;D:/ProgramFi
    les/JetBrains/IDEA/lib/annotations.jar;D:/ProgramFiles/JetBrains/IDEA/plugins/java/lib/jps-builders-6.jar;D:/ProgramFiles/JetBrains/IDEA/lib/log4j.jar;D:/ProgramFiles/JetBrains/IDEA/lib/maven-resolver-util-1.3.3.jar;D:/ProgramFiles/
    JetBrains/IDEA/lib/maven-resolver-impl-1.3.3.jar;D:/ProgramFiles/JetBrains/IDEA/lib/oro-2.0.8.jar;D:/ProgramFiles/JetBrains/IDEA/lib/idea_rt.jar;D:/ProgramFiles/JetBrains/IDEA/lib/plexus-utils-3.2.0.jar;D:/ProgramFiles/JetBrains/IDE
    A/lib/netty-buffer-4.1.47.Final.jar;D:/ProgramFiles/JetBrains/IDEA/lib/netty-resolver-4.1.47.Final.jar
    8520 chaper02.ThreadDeadLock

## 3 jcmd pid help——某一进程能使用的命令 ##

E:\JVMDemo3>jcmd 8520 help
    8520:
    The following commands are available:
    JFR.stop
    JFR.start
    JFR.dump
    JFR.check
    VM.native_memory
    VM.check_commercial_features
    VM.unlock_commercial_features
    ManagementAgent.stop
    ManagementAgent.start_local
    ManagementAgent.start
    VM.classloader_stats
    GC.rotate_log
    Thread.print
    GC.class_stats
    GC.class_histogram
    GC.heap_dump
    GC.finalizer_info
    GC.heap_info
    GC.run_finalization
    GC.run
    VM.uptime
    VM.dynlibs
    VM.flags
    VM.system_properties
    VM.command_line
    VM.version
    help

## 4 Thread.print——打印线程信息 ##

E:\JVMDemo3>jcmd 8520 Thread.print
    8520:
    2021-08-23 08:34:08
    Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.251-b08 mixed mode):
    
    "DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x000000000309e800 nid=0x9e8 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Thread-1" #13 prio=5 os_prio=0 tid=0x000000001e395000 nid=0x2a6c waiting for monitor entry [0x000000001f2ef000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at chaper02.ThreadDeadLock$2.run(ThreadDeadLock.java:48)
            - waiting to lock <0x00000007707ffcc8> (a java.lang.StringBuilder)
            - locked <0x00000007707ffd10> (a java.lang.StringBuilder)
    
    "Thread-0" #12 prio=5 os_prio=0 tid=0x000000001e392000 nid=0x3b74 waiting for monitor entry [0x000000001f1ef000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at chaper02.ThreadDeadLock$1.run(ThreadDeadLock.java:25)
            - waiting to lock <0x00000007707ffd10> (a java.lang.StringBuilder)
            - locked <0x00000007707ffcc8> (a java.lang.StringBuilder)
    
    "Service Thread" #11 daemon prio=9 os_prio=0 tid=0x000000001e35f800 nid=0x3ce0 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x000000001e2d5000 nid=0x1c04 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x000000001e2cf000 nid=0x3b68 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x000000001e2c2800 nid=0x32e4 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x000000001e2bf000 nid=0xa30 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x000000001e2ce000 nid=0x2d64 runnable [0x000000001eaee000]
       java.lang.Thread.State: RUNNABLE
            at java.net.SocketInputStream.socketRead0(Native Method)
            at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
            at java.net.SocketInputStream.read(SocketInputStream.java:171)
            at java.net.SocketInputStream.read(SocketInputStream.java:141)
            at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
            at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
            at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
            - locked <0x00000007706f2d58> (a java.io.InputStreamReader)
            at java.io.InputStreamReader.read(InputStreamReader.java:184)
            at java.io.BufferedReader.fill(BufferedReader.java:161)
            at java.io.BufferedReader.readLine(BufferedReader.java:324)
            - locked <0x00000007706f2d58> (a java.io.InputStreamReader)
            at java.io.BufferedReader.readLine(BufferedReader.java:389)
            at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:61)
    
    "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x000000001e229000 nid=0x1b3c waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001e227800 nid=0x1690 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x000000001c40e000 nid=0x3efc in Object.wait() [0x000000001e7ef000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x0000000770588ee0> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
            - locked <0x0000000770588ee0> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
            at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)
    
    "Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x000000001e210800 nid=0x9a0 in Object.wait() [0x000000001e6ef000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x0000000770586c00> (a java.lang.ref.Reference$Lock)
            at java.lang.Object.wait(Object.java:502)
            at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
            - locked <0x0000000770586c00> (a java.lang.ref.Reference$Lock)
            at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
    
    "VM Thread" os_prio=2 tid=0x000000001c408800 nid=0x3cec runnable
    
    "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00000000031f8800 nid=0x1c8c runnable
    
    "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00000000031fa000 nid=0x395c runnable
    
    "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00000000031fb800 nid=0x2ec4 runnable
    
    "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00000000031fd000 nid=0x124c runnable
    
    "GC task thread#4 (ParallelGC)" os_prio=0 tid=0x0000000003200800 nid=0xbcc runnable
    
    "GC task thread#5 (ParallelGC)" os_prio=0 tid=0x0000000003201800 nid=0x29f8 runnable
    
    "GC task thread#6 (ParallelGC)" os_prio=0 tid=0x0000000003205000 nid=0x1eb4 runnable
    
    "GC task thread#7 (ParallelGC)" os_prio=0 tid=0x0000000003206000 nid=0x3d28 runnable
    
    "VM Periodic Task Thread" os_prio=2 tid=0x000000001e38d800 nid=0x2614 waiting on condition
    
    JNI global references: 12
    
    Found one Java-level deadlock:
    =============================
    "Thread-1":
      waiting to lock monitor 0x00000000032de9c8 (object 0x00000007707ffcc8, a java.lang.StringBuilder),
      which is held by "Thread-0"
    "Thread-0":
      waiting to lock monitor 0x00000000032dd5d8 (object 0x00000007707ffd10, a java.lang.StringBuilder),
      which is held by "Thread-1"
    
    Java stack information for the threads listed above:
    ===================================================
    "Thread-1":
            at chaper02.ThreadDeadLock$2.run(ThreadDeadLock.java:48)
            - waiting to lock <0x00000007707ffcc8> (a java.lang.StringBuilder)
            - locked <0x00000007707ffd10> (a java.lang.StringBuilder)
    "Thread-0":
            at chaper02.ThreadDeadLock$1.run(ThreadDeadLock.java:25)
            - waiting to lock <0x00000007707ffd10> (a java.lang.StringBuilder)
            - locked <0x00000007707ffcc8> (a java.lang.StringBuilder)
    
    Found 1 deadlock.

## 5 GC.class\_histogram——统计对象情况 ##

E:\JVMDemo3>jcmd 8520 GC.class_histogram
    8520:
    
    
    num     #instances         #bytes  class name
    ----------------------------------------------
       1:          4542         433488  [C
       2:           419         135648  [B
       3:          4391         105384  java.lang.String
       4:           692          79216  java.lang.Class
       5:           627          41144  [Ljava.lang.Object;
    .......
    266:             1             16  sun.util.locale.provider.SPILocaleProviderAdapter
    267:             1             16  sun.util.locale.provider.TimeZoneNameUtility$TimeZoneNameGetter
    268:             1             16  sun.util.resources.LocaleData
    269:             1             16  sun.util.resources.LocaleData$LocaleDataResourceBundleControl
    Total         15074         985176

## 6 GC.heap\_dump——创建dump文件 ##

E:\JVMDemo3>jcmd 8520 GC.heap_dump d:\6.hprof
    8520:
    Heap dump file created

Heap dump file created

![20210823084902764.png][]

## 7 VM.uptime——查看进程运行时间 ##

E:\JVMDemo3>jcmd 8520 VM.uptime
    8520:
    687.778 s

## 8 VM.system\_properties——查看虚拟机系统属性 ##

E:\JVMDemo3>jcmd 8520 VM.system_properties
    8520:
    #Mon Aug 23 08:44:26 CST 2021
    java.runtime.name=Java(TM) SE Runtime Environment
    sun.boot.library.path=D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\bin
    java.vm.version=25.251-b08
    java.vm.vendor=Oracle Corporation
    java.vendor.url=http\://java.oracle.com/
    path.separator=;
    java.vm.name=Java HotSpot(TM) 64-Bit Server VM
    file.encoding.pkg=sun.io
    user.script=
    user.country=CN
    sun.java.launcher=SUN_STANDARD
    sun.os.patch.level=
    java.vm.specification.name=Java Virtual Machine Specification
    user.dir=E\:\\JVMDemo3
    java.runtime.version=1.8.0_251-b08
    java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment
    java.endorsed.dirs=D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\endorsed
    os.arch=amd64
    java.io.tmpdir=C\:\\Users\\CHENGQ~1\\AppData\\Local\\Temp\\
    line.separator=\r\n
    java.vm.specification.vendor=Oracle Corporation
    user.variant=
    os.name=Windows 10
    sun.jnu.encoding=GBK
    java.library.path=D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\bin;C\:\\WINDOWS\\Sun\\Java\\bin;C\:\\WINDOWS\\system32;C\:\\WINDOWS;C\:\\Program Files (x86)\\Common Files\\NetSarang;D\:\\Program\\NetSarang\\Xshell 6\\;C\:\\WINDOWS\\system
    32;C\:\\WINDOWS;C\:\\WINDOWS\\System32\\Wbem;C\:\\WINDOWS\\System32\\WindowsPowerShell\\v1.0\\;C\:\\WINDOWS\\System32\\OpenSSH\\;d\:\\Program Files\\Git\\cmd;D\:\\Program Files\\TortoiseGit\\bin;D\:\\Program Files\\nodejs\\;D\:\\Pro
    gram Files\\TortoiseSVN\\bin;D\:\\program\\go\\bin;C\:\\Users\\chengqiuming\\AppData\\Local\\Microsoft\\WindowsApps;d\:\\Program Files\\JetBrains\\IntelliJ IDEA Educational Edition 2020.1.1\\bin;;D\:\\MySQL\\MySQLServer 5.7\\bin;D\:
    \\program\\apache-maven-3.6.3\\bin;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\bin;d\:\\Program Files\\JetBrains\\IntelliJ IDEA Community Edition 2020.1.1\\bin;;C\:\\Users\\chengqiuming\\AppData\\Roaming\\npm;D\:\\ProgramFiles\\Java\\jdk
    1.8.0_251\\jre\\bin;C\:\\Users\\chengqiuming\\AppData\\Local\\Programs\\Microsoft VS Code\\bin;D\:\\program\\go\\bin;;.
    java.specification.name=Java Platform API Specification
    java.class.version=52.0
    sun.management.compiler=HotSpot 64-Bit Tiered Compilers
    os.version=10.0
    user.home=C\:\\Users\\chengqiuming
    user.timezone=Asia/Shanghai
    java.awt.printerjob=sun.awt.windows.WPrinterJob
    file.encoding=UTF-8
    java.specification.version=1.8
    java.class.path=D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\charsets.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\deploy.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext\\access-bridge-64.jar;D\:\\ProgramFiles\\
    Java\\jdk1.8.0_251\\jre\\lib\\ext\\cldrdata.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext\\dnsns.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext\\jaccess.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext\\
    jfxrt.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext\\localedata.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext\\nashorn.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext\\sunec.jar;D\:\\ProgramFiles\\Java
    \\jdk1.8.0_251\\jre\\lib\\ext\\sunjce_provider.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext\\sunmscapi.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext\\sunpkcs11.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\l
    ib\\ext\\zipfs.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\javaws.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\jce.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\jfr.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\
    jre\\lib\\jfxswt.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\jsse.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\management-agent.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\plugin.jar;D\:\\ProgramFiles\\Java
    \\jdk1.8.0_251\\jre\\lib\\resources.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\rt.jar;E\:\\JVMDemo3\\out\\production\\JVMDemo3;D\:\\ProgramFiles\\JetBrains\\IDEA\\lib\\idea_rt.jar
    user.name=chengqiuming
    java.vm.specification.version=1.8
    sun.java.command=chaper02.ThreadDeadLock
    java.home=D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre
    sun.arch.data.model=64
    user.language=zh
    java.specification.vendor=Oracle Corporation
    awt.toolkit=sun.awt.windows.WToolkit
    java.vm.info=mixed mode
    java.version=1.8.0_251
    java.ext.dirs=D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\ext;C\:\\WINDOWS\\Sun\\Java\\lib\\ext
    sun.boot.class.path=D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\resources.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\rt.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\sunrsasign.jar;D\:\\ProgramFiles\\Java\\jdk1
    .8.0_251\\jre\\lib\\jsse.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\jce.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\charsets.jar;D\:\\ProgramFiles\\Java\\jdk1.8.0_251\\jre\\lib\\jfr.jar;D\:\\ProgramFiles\\Java\\jd
    k1.8.0_251\\jre\\classes
    java.vendor=Oracle Corporation
    file.separator=\\
    java.vendor.url.bug=http\://bugreport.sun.com/bugreport/
    sun.io.unicode.encoding=UnicodeLittle
    sun.cpu.endian=little
    sun.desktop=windows
    sun.cpu.isalist=amd64

## 9 VM.flags——虚拟机启动参数 ##

E:\JVMDemo3>jcmd 8520 VM.flags
    8520:
    -XX:CICompilerCount=4 -XX:InitialHeapSize=251658240 -XX:MaxHeapSize=4009754624 -XX:MaxNewSize=1336410112 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=83886080 -XX:OldSize=167772160 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops
    -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

[https_docs.oracle.com_en_java_javase_11_tools_jcmd.html]: https://docs.oracle.com/en/java/javase/11/tools/jcmd.html
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70]: /images/20220829/437d9eb812884c6a8780dd9f445b1c72.png
[20210823084902764.png]: /images/20220829/43101bb7f5b54b26bd992f46241a189d.png