查看运行的java程序的启动命令
jps -lvm
运行时查看JVM配置
语法如下:
jinfo -flag <name> PID
如:
jinfo -flag CMSAbortablePrecleanWaitMillis 11715
查看全部非默认配置:
jinfo -flags PID
或者:
jcmd PID VM.flags
运行时修改JVM配置
首先并不是所有JVM配置都能在运行时动态修改的,需要查看哪些配置是可以运行时动态修改的:
列出可运行时调整的JVM配置(linux)
java -XX:+PrintFlagsInitial | grep manageable
结果如下:
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| 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}
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可以看到参数的类型主要分为bool和非bool(intx,uintx,ccstr)。
运行时修改bool型配置
用加减(+/-)表示开关:
jinfo -flag [+|-]<name> PID
运行时修改intx/ccstr/uintx型配置
jinfo -flag <name>=<value> PID
示例
比如我们有一个java进程11715,我们突然想查看它的gc情况,但是之前又没有打开gc日志,只重定向了控制台日志,这个时候可以动态打开:
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| jinfo -flag +PrintGC 11715
jinfo -flag +PrintGCDateStamps 11715
jinfo -flag +PrintGCDetails 11715
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拿到日志:
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| 2018-11-25T20:21:41.772+0800: [GC (Allocation Failure) [PSYoungGen: 45952K->1856K(48128K)] 248269K->204197K(309248K), 0.0423007 secs] [Times: user=0.88 sys=0.02, real=0.06 secs]
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调试完后再关掉即可:
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| jinfo -flag -PrintGC 11715
jinfo -flag -PrintGCDateStamps 11715
jinfo -flag -PrintGCDetails 11715
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