（转）JVM有关问题诊断常用命令：jinfo,j地图,jstack

1.jinfo

描述：输出给定 java 进程所有的配置信息。包括 java 系统属性和 jvm 命令行标记等。

用法：

jinfo [ option ] pid

jinfo [ option ] executable core

jinfo [ option ] [server-id@]remote-hostname-or-IP

例子：

jinfo pid

得到结果如下：

    JVM version is 14.0-b16  
      
    Java System Properties:  
      
    java.runtime.name = Java(TM) SE Runtime Environment  
      
    sun.boot.library.path = /work/ProgramFiles/jdk1.6.0_14/jre/lib/i386  
      
    java.vm.version = 14.0-b16  
      
    java.vm.vendor = Sun Microsystems Inc.  
      
    java.vendor.url = http://java.sun.com/  
      
    path.separator = :  
      
    java.vm.name = Java HotSpot(TM) Server VM  
      
    file.encoding.pkg = sun.io  
      
    sun.java.launcher = SUN_STANDARD  
      
    user.country = CN  
      
    sun.os.patch.level = unknown  
      
    java.vm.specification.name = Java Virtual Machine Specification  
      
    user.dir = /work/RateWorkspace/branches/rate/daemon  
      
    java.runtime.version = 1.6.0_14-b08  
      
    java.awt.graphicsenv = sun.awt.X11GraphicsEnvironment  
      
    java.endorsed.dirs = /work/ProgramFiles/jdk1.6.0_14/jre/lib/endorsed  
      
    os.arch = i386  
      
    java.io.tmpdir = /tmp  
      
    line.separator =   
      
      
      
    java.vm.specification.vendor = Sun Microsystems Inc.  
      
    os.name = Linux  
      
    sun.jnu.encoding = UTF-8  
      
    java.library.path = /work/ProgramFiles/jdk1.6.0_14/jre/lib/i386/server:/work/ProgramFiles/jdk1.6.0_14/jre/lib/i386:/work/ProgramFiles/jdk1.6.0_14/jre/../lib/i386:/usr/lib/jvm/java-6-openjdk/jre/lib/i386/client:/usr/lib/jvm/java-6-openjdk/jre/lib/i386:/usr/lib/xulrunner-addons:/usr/lib/xulrunner-addons:/usr/java/packages/lib/i386:/lib:/usr/lib  
      
    java.specification.name = Java Platform API Specification  
      
    java.class.version = 50.0  
      
    sun.management.compiler = HotSpot Tiered Compilers  
      
    os.version = 2.6.28-19-generic  
      
    user.home = /home/yblin  
      
    user.timezone = PRC  
      
    java.awt.printerjob = sun.print.PSPrinterJob  
      
    file.encoding = GBK  
      
    java.specification.version = 1.6  
      
    java.class.path =   
      
    user.name = yblin  
      
    java.vm.specification.version = 1.0  
      
    java.home = /work/ProgramFiles/jdk1.6.0_14/jre  
      
    sun.arch.data.model = 32  
      
    user.language = zh  
      
    java.specification.vendor = Sun Microsystems Inc.  
      
    java.vm.info = mixed mode  
      
    java.version = 1.6.0_14  
      
    java.ext.dirs = /work/ProgramFiles/jdk1.6.0_14/jre/lib/ext:/usr/java/packages/lib/ext  
      
    sun.boot.class.path = /work/ProgramFiles/jdk1.6.0_14/jre/lib/resources.jar:/work/ProgramFiles/jdk1.6.0_14/jre/lib/rt.jar:/work/ProgramFiles/jdk1.6.0_14/jre/lib/sunrsasign.jar:/work/ProgramFiles/jdk1.6.0_14/jre/lib/jsse.jar:/work/ProgramFiles/jdk1.6.0_14/jre/lib/jce.jar:/work/ProgramFiles/jdk1.6.0_14/jre/lib/charsets.jar:/work/ProgramFiles/jdk1.6.0_14/jre/classes  
      
    java.vendor = Sun Microsystems Inc.  
      
    file.separator = /  
      
    java.vendor.url.bug = http://java.sun.com/cgi-bin/bugreport.cgi  
      
    sun.io.unicode.encoding = UnicodeLittle  
      
    sun.cpu.endian = little  
      
    sun.desktop = gnome  
      
    sun.cpu.isalist =   
      
      
    VM Flags:  
      
    -agentlib:jdwp=transport=dt_socket,suspend=y,address=localhost:55948 -ea -Dfile.encoding=GBK  

这个命令包含了 JDK 和 JVM 运行起来时的一些属性。

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2.jmap

描述 ：输出给定 java 进程所有的内存使用信息。

使用：

??? jmap [ option ] pid

??? jmap [ option ] executable core

??? jmap [ option ] [server-id@]remote-hostname-or-IP

?

?

<no option>

没有可选项时，会输出所有共享的对象映射。

开始地址，映射大小，全路径。

直接 jmap pid得到如下结果：

0x08048000???? 46K? /work/ProgramFiles/jdk1.6.0_14/bin/java

0xb6763000???? 74K? /work/ProgramFiles/jdk1.6.0_14/jre/lib/i386/libzip.so

0xb6774000???? 41K? /lib/tls/i686/cmov/libnss_files-2.9.so

0xb6780000???? 37K? /lib/tls/i686/cmov/libnss_nis-2.9.so

0xb678b000???? 29K? /lib/tls/i686/cmov/libnss_compat-2.9.so

目前还说不是很理解这个执行结果是什么意思。经询问同事了解，是加载的文件的信息。

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-heap 选项

jmap -heap pid : 查看堆的配置和大当前各个区块的使用情况，如伊甸区、老年代，永久代。可以用此来判断内存目前的使用情况以及垃圾回收情况：

jmap -heap pid,得到如下结果：

    <strong>Heap Configuration:  
      
       MinHeapFreeRatio = 40  
      
       MaxHeapFreeRatio = 70  
      
       MaxHeapSize      = 859832320 (820.0MB)  
      
       NewSize          = 1048576 (1.0MB)  
      
       MaxNewSize       = 4294901760 (4095.9375MB)  
      
       OldSize          = 4194304 (4.0MB)  
      
       NewRatio         = 8  
      
       SurvivorRatio    = 8  
      
       PermSize         = 16777216 (16.0MB)  
      
       MaxPermSize      = 67108864 (64.0MB)  
      
      
    Heap Usage:  
      
    PS Young Generation  
      
    Eden Space:  
      
       capacity = 9043968 (8.625MB)  
      
       used     = 6820384 (6.504425048828125MB)  
      
       free     = 2223584 (2.120574951171875MB)  
      
       75.41362375452898% used  
      
    From Space:  
      
       capacity = 720896 (0.6875MB)  
      
       used     = 704680 (0.6720352172851562MB)  
      
       free     = 16216 (0.01546478271484375MB)  
      
       97.7505770596591% used  
      
    To Space:  
      
       capacity = 720896 (0.6875MB)  
      
       used     = 0 (0.0MB)  
      
       free     = 720896 (0.6875MB)  
      
       0.0% used  
      
    PS Old Generation  
      
       capacity = 47710208 (45.5MB)  
      
       used     = 589184 (0.5618896484375MB)  
      
       free     = 47121024 (44.9381103515625MB)  
      
       1.2349223042582418% used  
      
    PS Perm Generation  
      
       capacity = 16777216 (16.0MB)  
      
       used     = 5179648 (4.939697265625MB)  
      
       free     = 11597568 (11.060302734375MB)  
      
       30.87310791015625% used  
      
    </strong>  

-histo 选项

内存使用的柱状图，包含每个类，对象使用的内存大小。 VM 内部的类名以 * 前缀开头。

-permstat 选项

输出所有类装载器在堆里产生的对象

包括每个装载器的名字，活跃，地址，父装载器，和其总共加载的类大小。

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jmap -permstat pid

得到如下结果：

通过 jstack pid, 得到如下部分结果：

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可以看到只有线程 thrad75 是 RUNNABLE 状态的，其他的都是 BLOCKED 状态。因为其他的线程在竞争控制台输出的时候都被阻塞了。

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