Pre
有的时候，想看下自己没有设置的JVM参数的值， 或者有的时候想看下JVM某个参数的默认值 ，亦或想看下用户或者JVM修改的JVM参数 ？
咋办 ？
JVM在1.6.0_14以后提供了几个参数可以打印出来所有XX参数和对应的值
-XX:+PrintFlagsInitial 表示打印出所有参数选项的默认值 -XX:+PrintFlagsFinal 表示打印出所有参数选项在运行程序时生效的值
执行的话
java -XX:+PrintFlagsInitial java -XX:+PrintFlagsFinal
-XX:+PrintFlagsInitial 列出JVM参数的默认值
Java诞生了25年+， N多个参数 ，鬼记得住~
我们只需要直到常用的，会找就可以了。
我这用的1.8.0_181 列举出了 866个
部分截图如下
- 第一列表示参数的数据类型
- 第二列是名称
- 第三列”=”表示第四列是参数的默认值，如果是”:=” 表明了参数被用户或者JVM赋值了
- 第四列为值
- 第五列是参数的类别
-XX:+PrintFlagsFinal 列出运行程序时生效的值
”:=” 表明了参数被用户或者JVM赋值了， 也间接证明了Java8默认的垃圾回收器是Parallel + Parallel Old .
-XX:+PrintCommandLineFlags 列出被用户或者JVM优化设置过的详细的XX参数的名称和值
这一步其实就是列出 -XX:+PrintFlagsFinal的结果中第三列有":="的参数 。
也可以理解为打印命令行参数
列举附加隐藏参数
-XX:+UnlockDiagnosticVMOptions 解锁诊断参数 -XX:+UnlockExperimentalVMOptions 解锁实验参数 -XX:+UnlockInternalVMOptions 解锁内部参数
这个就是隐藏副本了 ，愿君多留意~
jinfo 查看正在运行的Java应用程序的扩展参数
当然了 还有其他参数 也可以看
jps + jinfo
jps
[root@artisan ~]# jps --help illegal argument: --help usage: jps [-help] jps [-q] [-mlvV] [<hostid>] Definitions: <hostid>: <hostname>[:<port>]
最常用的jps , 查看PID
输出更多信息
jps -v
【demo】
[root@artisan ~]# jps 5811 kooteam.jar 6043 Jps [root@artisan ~]# jps -v 5811 kooteam.jar -Xms1024m -Xmx1024m 6054 Jps -Denv.class.path=.:/usr/java/jdk1.8.0_221-amd64/jre/lib:/usr/java/jdk1.8.0_221-amd64/lib:/usr/java/jdk1.8.0_221-amd64/lib/tools.jar -Dapplication.home=/usr/java/jdk1.8.0_221-amd64 -Xms8m [root@artisan ~]#
jinfo
[root@artisan ~]# 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 [root@artisan ~]#
【查看jvm的参数】
[root@artisan ~]# jinfo -flags 5811 Attaching to process ID 5811, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.221-b11 Non-default VM flags: -XX:CICompilerCount=2 -XX:InitialHeapSize=1073741824 -XX:MaxHeapSize=1073741824 -XX:MaxNewSize=357892096 -XX:MinHeapDeltaBytes=196608 -XX:NewSize=357892096 -XX:OldSize=715849728 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps Command line: -Xms1024m -Xmx1024m [root@artisan ~]#
【查看java系统参数】
[root@artisan ~]# jinfo -sysprops 5811 Attaching to process ID 5811, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.221-b11 java.runtime.name = Java(TM) SE Runtime Environment java.vm.version = 25.221-b11 sun.boot.library.path = /usr/java/jdk1.8.0_221-amd64/jre/lib/amd64 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 = /root java.vm.specification.name = Java Virtual Machine Specification java.runtime.version = 1.8.0_221-b11 java.awt.graphicsenv = sun.awt.X11GraphicsEnvironment os.arch = amd64 java.endorsed.dirs = /usr/java/jdk1.8.0_221-amd64/jre/lib/endorsed 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 sun.nio.ch.bugLevel = java.specification.name = Java Platform API Specification java.class.version = 52.0 sun.management.compiler = HotSpot 64-Bit Tiered Compilers os.version = 3.10.0-123.el7.x86_64 user.home = /root user.timezone = Asia/Shanghai java.awt.printerjob = sun.print.PSPrinterJob file.encoding = UTF-8 java.specification.version = 1.8 user.name = root java.class.path = ./kooteam.jar java.vm.specification.version = 1.8 sun.arch.data.model = 64 sun.java.command = ./kooteam.jar java.home = /usr/java/jdk1.8.0_221-amd64/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_221 java.ext.dirs = /usr/java/jdk1.8.0_221-amd64/jre/lib/ext:/usr/java/packages/lib/ext sun.boot.class.path = /usr/java/jdk1.8.0_221-amd64/jre/lib/resources.jar:/usr/java/jdk1.8.0_221-amd64/jre/lib/rt.jar:/usr/java/jdk1.8.0_221-amd64/jre/lib/sunrsasign.jar:/usr/java/jdk1.8.0_221-amd64/jre/lib/jsse.jar:/usr/java/jdk1.8.0_221-amd64/jre/lib/jce.jar:/usr/java/jdk1.8.0_221-amd64/jre/lib/charsets.jar:/usr/java/jdk1.8.0_221-amd64/jre/lib/jfr.jar:/usr/java/jdk1.8.0_221-amd64/jre/classes java.vendor = Oracle Corporation com.zaxxer.hikari.pool_number = 1 file.separator = / java.vendor.url.bug = http://bugreport.sun.com/bugreport/ sun.io.unicode.encoding = UnicodeLittle sun.cpu.endian = little sun.cpu.isalist = [root@artisan ~]#
