jinfo 查看、设置JVM参数

用法：

# jinfo -h
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

 例子：

$ jinfo -flag HeapDumpBeforeFullGC  29167  #查看HeapDumpBeforeFullGC
-XX:-HeapDumpBeforeFullGC
$ jinfo -flag +HeapDumpBeforeFullGC  29167  #打开HeapDumpBeforeFullGC
$ jinfo -flag HeapDumpBeforeFullGC  29167
-XX:+HeapDumpBeforeFullGC
$ jinfo -flag -HeapDumpBeforeFullGC  29167  #关闭HeapDumpBeforeFullGC
$ jinfo -flag HeapDumpBeforeFullGC  29167
-XX:-HeapDumpBeforeFullGC

 如果出现：

pid: well-known file is not secure

 请确认当前执行jinfo的命令的用户有 /tmp/hsperfdata_$USER/$PID 文件的权限

 如果出现：

Exception in thread "main" java.io.IOException: Command failed in target VM
        at sun.tools.attach.LinuxVirtualMachine.execute(LinuxVirtualMachine.java:218)
        at sun.tools.attach.HotSpotVirtualMachine.executeCommand(HotSpotVirtualMachine.java:213)
        at sun.tools.attach.HotSpotVirtualMachine.setFlag(HotSpotVirtualMachine.java:190)
        at sun.tools.jinfo.JInfo.flag(JInfo.java:123)
        at sun.tools.jinfo.JInfo.main(JInfo.java:76)

 说明参数不支持修改

 另外，jinfo可能在未来的jvm中移除。

 参考资料：

http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4109888

http://blog.tsunanet.net/2010/10/ioexception-well-known-file-is-not.html

http://docs.oracle.com/javase/6/docs/technotes/tools/share/jinfo.html

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