jinfo 观察修改运行中的java程序的运行环境参数的使用方法

小灰灰 2020-05-15 14:20 883阅读 0赞

#  jinfo

jinfo用于观察、**修改**运行中的java程序的运行环境参数：参数包括Java System属性和JVM命令行参数。

jinfo语法

jinfo [option] `<pid>`

其中`<option>` 是以下之一:

-flag `<name>`     打印指定name的 JVM flag

-flag [+|-]`<name>`   启用或者禁用指定name的 JVM flag

-flag `<name>=<value>` 设置指定名称的name flag 为给定的值

-flags        打印 JVM flags

-sysprops      打印Java 系统属性

`<no option>`      不指定任何option，则打印出所有的JVM flags和sysprops

-h | -help      打印帮助信息

**观察所有的java系统属性和非默认的JVM Flags**

```shell
[root@www wangxiaoxiao]# jinfo 15525

Attaching to process ID 15525, please wait...

Debugger attached successfully.

Server compiler detected.

JVM version is 25.65-b01

Java System Properties:

jboss.i18n.generate-proxies = true

java.runtime.name = Java(TM) SE Runtime Environment

java.vm.version = 25.65-b01

sun.boot.library.path = /usr/local/jdk8/jre/lib/amd64

java.protocol.handler.pkgs = null|org.springframework.boot.loader

java.vendor.url = http://java.oracle.com/

java.vm.vendor = Oracle Corporation

path.separator = :

file.encoding.pkg = sun.io

java.vm.name = Java HotSpot(TM) 64-Bit Server VM

sun.os.patch.level = unknown

sun.java.launcher = SUN_STANDARD

user.country = US

user.dir = /data/website

java.vm.specification.name = Java Virtual Machine Specification

PID = 15525

java.runtime.version = 1.8.0_65-b17

java.awt.graphicsenv = sun.awt.X11GraphicsEnvironment

os.arch = amd64

java.endorsed.dirs = /usr/local/jdk8/jre/lib/endorsed

org.jboss.logging.provider = slf4j

line.separator =

java.io.tmpdir = /tmp

java.vm.specification.vendor = Oracle Corporation

os.name = Linux

sun.jnu.encoding = UTF-8

java.library.path = /usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib

spring.beaninfo.ignore = true

java.specification.name = Java Platform API Specification

java.class.version = 52.0

sun.management.compiler = HotSpot 64-Bit Tiered Compilers

os.version = 2.6.32-431.23.3.el6.x86_64

user.home = /root

user.timezone = Asia/Harbin

catalina.useNaming = false

java.awt.printerjob = sun.print.PSPrinterJob

file.encoding = UTF-8

java.specification.version = 1.8

catalina.home = /tmp/tomcat.4517928592901920395.8081

user.name = root

java.class.path = website-0.0.1-SNAPSHOT.jar

java.vm.specification.version = 1.8

sun.arch.data.model = 64

sun.java.command = website-0.0.1-SNAPSHOT.jar

java.home = /usr/local/jdk8/jre

user.language = en

java.specification.vendor = Oracle Corporation

awt.toolkit = sun.awt.X11.XToolkit

java.vm.info = mixed mode

java.version = 1.8.0_65

java.ext.dirs = /usr/local/jdk8/jre/lib/ext

sun.boot.class.path = /usr/local/jdk8/jre/lib/resources.jar:/usr/local/jdk8/jre/lib/rt.jar:/usr/local/jdk8/jre/lib/sunrsasign.jar:/usr/local/jdk8/jre/lib/jsse.jar:/usr/local/jdk8/jre/lib/jce.jar:/usr/local/jdk8/jre/lib/charsets.jar:/usr/local/jdk8/jre/lib/jfr.jar:/usr/local/jdk8/jre/classes

java.awt.headless = true

java.vendor = Oracle Corporation

catalina.base = /tmp/tomcat.4517928592901920395.8081

file.separator = /

LOG_EXCEPTION_CONVERSION_WORD = %wEx

java.vendor.url.bug = http://bugreport.sun.com/bugreport/

sun.io.unicode.encoding = UnicodeLittle

sun.cpu.endian = little

sun.cpu.isalist =

VM Flags:

Non-default VM flags: -XX:CICompilerCount=2 -XX:+CMSClassUnloadingEnabled -XX:CMSInitiatingOccupancyFraction=70 -XX:+CMSParallelRemarkEnabled -XX:+DisableExplicitGC -XX:InitialHeapSize=134217728 -XX:MaxHeapSize=536870912 -XX:MaxNewSize=134217728 -XX:MinHeapDeltaBytes=196608 -XX:NewSize=134152192 -XX:OldPLABSize=16 -XX:OldSize=65536 -XX:-OmitStackTraceInFastThrow -XX:SoftRefLRUPolicyMSPerMB=0 -XX:SurvivorRatio=8 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseConcMarkSweepGC -XX:+UseParNewGC

Command line:  -Xms128m -Xmx512m -Xmn128m -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=70 -XX:+CMSParallelRemarkEnabled -XX:SoftRefLRUPolicyMSPerMB=0 -XX:+CMSClassUnloadingEnabled -XX:SurvivorRatio=8 -XX:+DisableExplicitGC -XX:-OmitStackTraceInFastThrow -Djava.ext.dirs=/usr/local/jdk8/jre/lib/ext
```

注意，这里的VM Flags只打印出非默认的参数。

**修改运行中的JVM Flags**

jinfo还能够修改一部分运行期间能够调整的虚拟机参数。例如系统启动时，并没有指定这样的参数-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/java/dump.hprof，这两个参数用于内存dump分析，后面讲解jmap的时候会介绍。

则可以通过jinfo命令进行修改：

```shell
jinfo -flag +HeapDumpOnOutOfMemoryError 15525

jinfo -flag HeapDumpPath=/java/dump.hprof 15525
```

注意：

1、如果运行过程中，通过jinfo修改了，则修改后的值只能通过jinfo看到，jps是看不到的，jps命令只能看到启动时的jvm参数。

2、很多运行参数是不能调整的，如果出现这种异常，说明不能调整：

```java
[root@www wangxiaoxiao]# jinfo -flag SurvivorRatio=7 15525
Exception in thread "main" com.sun.tools.attach.AttachOperationFailedException: flag 'SurvivorRatio' cannot be changed
```

最后，对于运行时的修改，jinfo命令好像存在一个bug，如下图所示，我们明明设置了HeapDumpPath=/java/dump.hprof，但是这里显示的却是null：

![](/images/1589552293373.png)

但是直接指定查看HeapDumpPath这个flag时，返回的又是我们设置的值。

![](/images/1589552278790.png)