1、jinfo介绍
The `jinfo` command prints Java configuration information for a specified Java process or core file or a remote debug server.
The configuration information includes Java system properties and Java Virtual Machine (JVM) command-line flags.
jinfo命令查看指定Java进程、核心文件或远程调试服务器的Java配置信息。
配置信息包括Java系统属性和Java虚拟机(JVM)命令行标志。
对于JVM来说就是：实时查看和调整JVM配置参数。
2、使用说明
[root@VM_0_12_centos ~]# 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
3、查看
jinfo -flag name PID 查看某个java进程的name属性的值
[root@VM_0_12_centos ~]# jinfo -flag MaxHeapSize 635
-XX:MaxHeapSize=268435456 // 256M
[root@VM_0_12_centos ~]# jinfo -flag InitialHeapSize 635
-XX:InitialHeapSize=67108864 //64M
4、修改
只有被标记为manageable的flags可以背实时修改
通过java -XX:+PrintFlagsInitial | grep manageable查看哪些是manageable类型的flags
[root@VM_0_12_centos ~]# java -XX:+PrintFlagsInitial | grep manageable
intx CMSAbortablePrecleanWaitMillis = 100 {manageable}
intx CMSTriggerInterval = -1 {manageable}
intx CMSWaitDuration = 2000 {manageable}
bool HeapDumpAfterFullGC = false {manageable}
bool HeapDumpBeforeFullGC = false {manageable}
bool HeapDumpOnOutOfMemoryError = false {manageable}
ccstr HeapDumpPath = {manageable}
uintx MaxHeapFreeRatio = 70 {manageable}
uintx MinHeapFreeRatio = 40 {manageable}
bool PrintClassHistogram = false {manageable}
bool PrintClassHistogramAfterFullGC = false {manageable}
bool PrintClassHistogramBeforeFullGC = false {manageable}
bool PrintConcurrentLocks = false {manageable}
bool PrintGC = false {manageable}
bool PrintGCDateStamps = false {manageable}
bool PrintGCDetails = false {manageable}
bool PrintGCID = false {manageable}
bool PrintGCTimeStamps = false {manageable}
开启或者关闭对应名称的参数
jinfo -flag [+|-]name PID修改指定参数的值
jinfo -flag name=value PID
[root@VM_0_12_centos ~]# jinfo -flag PrintGC 635
-XX:-PrintGC // 查看
[root@VM_0_12_centos ~]# jinfo -flag +PrintGC 635
[root@VM_0_12_centos ~]#
[root@VM_0_12_centos ~]# jinfo -flag PrintGC 635
-XX:+PrintGC //修改后
5、查看曾经操作过的一些参数
jinfo -flags PID
[root@VM_0_12_centos ~]# jinfo -flags 635
Attaching to process ID 635, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.74-b02
Non-default VM flags:`-XX:-PrintGC`
Command line: -Xms64m -Xmx256m
面对每一道题目，要学会把自己的思维发散出去。每一篇文章只当自己对知识的总结！
