1 Usage: jcmd <pid | main class> <command ...|PerfCounter.print|-f file>
   2    or: jcmd -l                                                    
   3    or: jcmd -h                                                    
   5   command must be a valid jcmd command for the selected jvm.      
   6   Use the command "help" to see which commands are available.   
   7   If the pid is 0, commands will be sent to all Java processes.   
   8   The main class argument will be used to match (either partially 
   9   or fully) the class used to start Java.                         
  10   If no options are given, lists Java processes (same as -l).     
  12   PerfCounter.print display the counters exposed by this process  
  13   -f  read and execute commands from the file                     
  14   -l  list JVM processes on the local machine                     
  15   -h  this help