我试图尝试使用jcmd VM.set_flag选项。但是遇到了一个错误,上面写着"只有'可写'标志可以设置"。什么是可写标志?
得到我的pid:
XXX@XXX-Air:~/javacode$ jcmd -l
6294 Test
6295 jdk.jcmd/sun.tools.jcmd.JCmd -l
尝试更改vm标志:
XXX@XXX-Air:~/javacode$ jcmd 6294 VM.set_flag ConcGCThreads 4
6294:
only 'writeable' flags can be set
XXX@XXX-Air:~/javacode$ jcmd 6294 VM.set_flag MaxNewSize 1G
6294:
only 'writeable' flags can be set
编辑:它适用于可管理的标志,下面是成功的命令。
XXXX@XXX-Air:~/javacode$ jcmd 11441 VM.flags -all | grep MinHeapFreeRatio
uintx MinHeapFreeRatio = 40 {manageable} {default}
XXXX@XXX-Air:~/javacode$ jcmd 11441 VM.set_flag MinHeapFreeRatio 45
11441:
Command executed successfully
XXXX@XXX-Air:~/javacode$ jcmd 11441 VM.flags -all | grep MinHeapFreeRatio
uintx MinHeapFreeRatio = 45
答案 0 :(得分:3)
可写标记标记为{manageable}
。
您可以使用jcmd 12345 VM.flags -all
列出所有标记。然后,您可以grep查找可管理的文件(在我的Oracle jdk8 VM上):
$ jcmd 12345 VM.flags -all | 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 = 100 {manageable}
uintx MinHeapFreeRatio = 0 {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}
答案 1 :(得分:2)
VM options上的文章指出: -
标记为 可管理 的标志通过JDK动态可写 管理界面(
com.sun.management.HotSpotDiagnosticMXBean
API) 还通过JConsole。
要查找所有此类标记,您可以使用
的VM.flags
打印VM标记选项及其当前值
以-all
为选项
打印VM支持的所有标志
使用命令: -
jcmd <pid> VM.flags -all