java 15: jinfo查看jvm配置参数和系统属性

一，jinfo查看帮助

[lhdop@blog ~]$ jinfo --help
Usage:
    jinfo <option> <pid>
       (to connect to a running process)
 
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 VM flags and system properties
    -? | -h | --help | -help to print this help message

说明：刘宏缔的架构森林是一个专注架构的博客，地址：https://www.cnblogs.com/architectforest

         对应的源码可以访问这里获取： https://github.com/liuhongdi/
         或: https://gitee.com/liuhongdi

说明：作者:刘宏缔 邮箱: 371125307@qq.com

二，jinfo的使用例子

1,打印vm全部的参数

[lhdop@blog ~]$ jinfo -flags 5426
VM Flags:
-XX:CICompilerCount=3 -XX:ConcGCThreads=1 -XX:G1ConcRefinementThreads=4 -XX:G1HeapRegionSize=2097152 -XX:GCDrainStackTargetSize=64 
-XX:InitialHeapSize=251658240 -XX:MarkStackSize=4194304 -XX:MaxHeapSize=4026531840 -XX:MaxNewSize=2415919104 -XX:MinHeapDeltaBytes=2097152 
-XX:MinHeapSize=8388608 -XX:NonNMethodCodeHeapSize=5832780 -XX:NonProfiledCodeHeapSize=122912730 -XX:ProfiledCodeHeapSize=122912730 
-XX:ReservedCodeCacheSize=251658240 -XX:+SegmentedCodeCache -XX:SoftMaxHeapSize=4026531840 -XX:+UseCompressedClassPointers 
-XX:+UseCompressedOops -XX:+UseG1GC

2,输出当前 jvm 的全部系统属性

[lhdop@blog ~]$ jinfo -syspros 5426
Java System Properties:
#Wed Mar 23 21:59:46 CST 2022
java.specification.version=15
sun.jnu.encoding=UTF-8
java.class.path=/data/store/back/jar/storeback-0.0.1-SNAPSHOT.jar
java.vm.vendor=Oracle Corporation
sun.arch.data.model=64
catalina.useNaming=false
java.vendor.url=https\://java.oracle.com/
user.timezone=Asia/Shanghai
os.name=Linux
java.vm.specification.version=15
sun.java.launcher=SUN_STANDARD
user.country=US
sun.boot.library.path=/usr/local/soft/jdk-15/lib
...

3,打印单个vm参数:

[lhdop@blog ~]$ jinfo -flag PrintGC 5426
-XX:-PrintGC

说明：-表示false,+表示true

[lhdop@blog ~]$ jinfo -flag MinHeapSize 5426
-XX:MinHeapSize=8388608

4,得到支持动态修改的vm参数

[lhdop@blog ~]$ java -XX:+PrintFlagsInitial | grep manageable
    uintx G1PeriodicGCInterval                     = 0                                      {manageable} {default}
   double G1PeriodicGCSystemLoadThreshold          = 0.000000                               {manageable} {default}
     bool HeapDumpAfterFullGC                      = false                                  {manageable} {default}
     bool HeapDumpBeforeFullGC                     = false                                  {manageable} {default}
     bool HeapDumpOnOutOfMemoryError               = false                                  {manageable} {default}
    ccstr HeapDumpPath                             =                                        {manageable} {default}
    uintx MaxHeapFreeRatio                         = 70                                     {manageable} {default}
    uintx MinHeapFreeRatio                         = 40                                     {manageable} {default}
     bool PrintClassHistogram                      = false                                  {manageable} {default}
     bool PrintConcurrentLocks                     = false                                  {manageable} {default}
     bool ShowCodeDetailsInExceptionMessages       = true                                   {manageable} {default}
   size_t SoftMaxHeapSize                          = 0                                      {manageable} {default}

其中标志为 manageable的参数，是可以用jinfo手动修改的，

可见只占一小部分，就不再演示了

三，查看java版本

[lhdop@blog tools]$ java --version
java 15 2020-09-15
Java(TM) SE Runtime Environment (build 15+36-1562)
Java HotSpot(TM) 64-Bit Server VM (build 15+36-1562, mixed mode, sharing)