一、简介

jinfo 是 JDK 自带的命令，可以用来查看正在运行的 java 应用程序的扩展参数，包括Java System属性和JVM命令行参数；也可以动态的修改正在运行的 JVM 一些参数。当系统崩溃时，jinfo可以从core文件里面知道崩溃的Java应用程序的配置信息。

jinfo -help

输出结果：

> jinfo -help
Usage:jinfo [option] <pid>(to connect to running process)jinfo [option] <executable <core>(to connect to a core file)jinfo [option] [server_id@]<remote server IP or hostname>(to connect to remote debug server)where <option> is one of:-flag <name>         to print the value of the named VM flag-flag [+|-]<name>    to enable or disable the named VM flag-flag <name>=<value> to set the named VM flag to the given value-flags               to print VM flags-sysprops            to print Java system properties<no option>          to print both of the above-h | -help           to print this help message

参数说明：

• -flag <name> ：打印指定名称的参数。
• -flag [+|-]<name> ：打开或关闭参数。
• -flag <name>=<value> ：设置参数。
• -flags ：打印当前指定java进程中已经设定的所有JVM参数信息。
• -sysprops ：打印当前java进程中设定的系统环境参数。
• <no option> ：打印上面两个选项。

二、常用命令

1、jinfo -flags pid : 打印当前指定java进程中已经设定的所有JVM参数信息

jinfo -flags 7663

输出结果：

Attaching to process ID 7663, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.121-b13
Non-default VM flags: -XX:CICompilerCount=4 -XX:InitialHeapSize=268435456 -XX:MaxHeapSize=4294967296 -XX:MaxNewSize=1431306240 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=89128960 -XX:OldSize=179306496 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:+UseParallelGC
Command line:  -javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=49834:/Applications/IntelliJ IDEA.app/Contents/bin -Dfile.encoding=UTF-8

2、jinfo -flag pid : 打印指定名称的参数

其中，<name> 不包含上图的前缀 -XX: 等，不是 jinfo -flag -XX:NewSize 7663，而是 jinfo -flag NewSize 7663，不包含 -XX: 。

jinfo -flag NewSize 7663

输出结果：

-XX:NewSize=89128960

3、jinfo -flag [+|-] pid : 打开或关闭参数

jinfo -flag +PrintGC 7663

执行上面命令后，执行如下命令查看结果：

jinfo -flags 7663

输出结果：

从图中我们可以看到参数已经打开。

4、jinfo -sysprops pid : 打印当前java进程中设定的系统环境参数

jinfo -sysprops 7663

输出结果：

Attaching to process ID 7663, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.121-b13
java.runtime.name = Java(TM) SE Runtime Environment
java.vm.version = 25.121-b13
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