2018-03-26

jmap命令

打印可共享内存map或堆内存细节信息。使用时可能需要root权限。

概要

jmap [options] pid

jmap [options] executable core

jmap [options] [pid] [server-id@] remote-hostname-or-IP

options 命令行选项。

pid Java进程号。

executable 可执行命令。

core 需要打印内存信息的core文件。

remote-hostname-or-IP 多个调试服务器在同一个远程主机上运行时使用的可选唯一标识。

描述

jmap主要用于打印指定Java进程(或核心文件、远程调试服务器)的共享对象内存映射或堆内存细节。如果进程运行在64位虚拟机上，则可能需要使用-J-d64选项。

Options

< no option > 如果使用不带选项参数的jmap打印共享对象映射，将会打印目标虚拟机中加载的每个共享对象的起始地址、映射大小以及共享对象文件的路径全称。

-> % sudo jmap 3431
Attaching to process ID 3431, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.66-b17
0x0000000000400000	7K	/home/lyyljs/lan/jdk8/bin/java
0x00007f95eee86000	48K	/home/lyyljs/lan/jdk8/jre/lib/amd64/libmanagement.so
0x00007f95ef592000	86K	/lib/x86_64-linux-gnu/libgcc_s.so.1
0x00007f95ef7a8000	250K	/home/lyyljs/lan/jdk8/jre/lib/amd64/libsunec.so
0x00007f95efbef000	90K	/home/lyyljs/lan/jdk8/jre/lib/amd64/libnio.so
0x00007f9611931000	113K	/home/lyyljs/lan/jdk8/jre/lib/amd64/libnet.so
0x00007f96279cc000	121K	/home/lyyljs/lan/jdk8/jre/lib/amd64/libzip.so
0x00007f9627be7000	50K	/lib/x86_64-linux-gnu/libnss_files-2.15.so
0x00007f9627df4000	46K	/lib/x86_64-linux-gnu/libnss_nis-2.15.so
0x00007f962c0ce000	94K	/lib/x86_64-linux-gnu/libnsl-2.15.so
0x00007f962c2e8000	34K	/lib/x86_64-linux-gnu/libnss_compat-2.15.so
0x00007f962c4f1000	220K	/home/lyyljs/lan/jdk8/jre/lib/amd64/libjava.so
0x00007f962c71d000	64K	/home/lyyljs/lan/jdk8/jre/lib/amd64/libverify.so
0x00007f962c92c000	31K	/lib/x86_64-linux-gnu/librt-2.15.so
0x00007f962cb34000	1006K	/lib/x86_64-linux-gnu/libm-2.15.so
0x00007f962ce30000	16516K	/home/lyyljs/lan/jdk8/jre/lib/amd64/server/libjvm.so
0x00007f962de0a000	1772K	/lib/x86_64-linux-gnu/libc-2.15.so
0x00007f962e1ca000	14K	/lib/x86_64-linux-gnu/libdl-2.15.so
0x00007f962e3ce000	100K	/home/lyyljs/lan/jdk8/lib/amd64/jli/libjli.so
0x00007f962e5e4000	132K	/lib/x86_64-linux-gnu/libpthread-2.15.so
0x00007f962e801000	145K	/lib/x86_64-linux-gnu/ld-2.15.so

-dump:[live,] format=b, file=filename 以hprof二进制格式转储Java堆到指定filename的文件中。live子选项是可选的。如果指定了live子选项，堆中只有活动的对象会被转储。可使用jhat,Visual GC,eclipse Memory Analyzer等工具进行分析。

-> % jmap -dump:format=b,file=test.bin 3431
Dumping heap to/home/lyyljs/test.bin ...
Heap dump file created
-> % jhat test.bin 
Reading from test.bin...
Dump file created Mon Mar 26 14:09:49 CST 2018
Snapshot read, resolving...
Resolving 1250155 objects...
Chasing references, expect 250 dots..........................................................................................................................................................................................................................................................
Eliminating duplicate references..........................................................................................................................................................................................................................................................
Snapshot resolved.
Started HTTP server on port 7000
Server is ready.#可以通过ip:7000访问查看分析。

-finalizerinfo 打印等待终结（finalization）的对象信息。

-> % sudo jmap -finalizerinfo 3431
Attaching to process ID 3431, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.66-b17
Number of objects pending for finalization: 0

-heap 打印一个堆的摘要信息,，包括使用的GC算法、堆配置信息和分代堆使用信息。

-> % sudo jmap -heap 3431 
Attaching to process ID 3431, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.66-b17

using thread-local object allocation.
Parallel GC with 2 thread(s)

Heap Configuration:
   MinHeapFreeRatio         = 0
   MaxHeapFreeRatio         = 100
   MaxHeapSize              = 268435456 (256.0MB)
   NewSize                  = 134217728 (128.0MB)
   MaxNewSize               = 134217728 (128.0MB)
   OldSize                  = 134217728 (128.0MB)
   NewRatio                 = 2
   SurvivorRatio            = 10
   MetaspaceSize            = 62914560 (60.0MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 131072000 (125.0MB)
   used     = 73502080 (70.0970458984375MB)
   free     = 57569920 (54.9029541015625MB)
   56.07763671875% used
From Space:
   capacity = 1572864 (1.5MB)
   used     = 987520 (0.9417724609375MB)
   free     = 585344 (0.5582275390625MB)
   62.784830729166664% used
To Space:
   capacity = 1572864 (1.5MB)
   used     = 0 (0.0MB)
   free     = 1572864 (1.5MB)
   0.0% used
PS Old Generation
   capacity = 134217728 (128.0MB)
   used     = 30292192 (28.888885498046875MB)
   free     = 103925536 (99.11111450195312MB)
   22.56944179534912% used

19790 interned Strings occupying 1802464 bytes.

-histo[:live] 打印堆的柱状图。其中包括每个Java类,对象数量,内存大小,完全限定的类名。打印的JVM内部类名称将会带有一个****前缀。如果指定了live*子选项，则只计算活动的对象。

-> % jmap -histo 3431 > test.histo
-> % less test.histo 
 num     #instances         #bytes  class name
 序号	实例数量			字节数		类名
----------------------------------------------
   1:        289741       37478104  [C
   2:         97559       31077664  [B
   3:        192282        4614768  java.lang.String
   4:         21694        3215944  [I
   5:         76700        2454400  java.util.HashMap$Node
   6:         31789        1531960  [Ljava.lang.Object;
   7:         20941        1507752  java.lang.reflect.Field
   8:         15375        1353000  java.lang.reflect.Method
   9:         11452        1214248  [Ljava.util.HashMap$Node;
  10:          7957         888752  java.lang.Class
  11:         27131         868192  java.util.concurrent.ConcurrentHashMap$Node
  ...
  3299:             1             16  sun.util.locale.provider.TimeZoneNameUtility$TimeZoneNameGetter
3300:             1             16  sun.util.resources.LocaleData
3301:             1             16  sun.util.resources.LocaleData$LocaleDataResourceBundleControl
Total       1213485      100989464

-clstats 打印Java堆的类加载统计信息。

-> % sudo jmap -clstats 3431
Attaching to process ID 3431, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.66-b17
finding class loader instances ..
done.
computing per loader stat ..done.
please wait.. computing liveness.........liveness analysis may be inaccurate ...
class_loader	classes	bytes	parent_loader	alive?	type
类加载器地址	加载类数量	加载类大小	父加载器	是否存活	类加载器类型

<bootstrap>	2778	4860705	  null  	live	<internal>
0x00000000f02caf28	1	1473	0x00000000f056f510	dead	sun/reflect/DelegatingClassLoader@0x0000000100009df8
0x00000000f02cbd38	1	1471	  null  	dead	sun/reflect/DelegatingClassLoader@0x0000000100009df8
0x00000000f0174730	0	0	0x00000000f056f510	live	java/util/ResourceBundle$RBClassLoader@0x00000001000c72f8
0x00000000f05410b8	138	282890	  null  	live	sun/misc/Launcher$ExtClassLoader@0x000000010000fa30
0x00000000f056f510	4783	7865232	0x00000000f05410b8	live	sun/misc/Launcher$AppClassLoader@0x000000010000f688
...

total = 167	8001	13646309	    N/A    	alive=8, dead=159	    N/A

-F 强制模式。如果指定的pid没有响应使用该选项，live子选项不支持该模式。

-h|-help 打印帮助信息。

-Jflag 指定传递给运行jmap的JVM的参数。

参考

Oracle jmap官方文档