1. jcmd
(base) PS C:\Users\zishi> jcmd -h Usage: jcmd <pid | main class> <command ...|PerfCounter.print|-f file> or: jcmd -l or: jcmd -h command must be a valid jcmd command for the selected jvm. Use the command "help" to see which commands are available. If the pid is 0, commands will be sent to all Java processes. The main class argument will be used to match (either partially or fully) the class used to start Java. If no options are given, lists Java processes (same as -l). PerfCounter.print display the counters exposed by this process -f read and execute commands from the file -l list JVM processes on the local machine -? -h --help print this help message
How to use
Usage: jcmd <pid | main class> <command ...|PerfCounter.print|-f file>
PerfCounter.print
(base) PS C:\Users\zishi> jcmd 8196 PerfCounter.print 8196: java.ci.totalTime=423311945 java.cls.loadedClasses=13392 java.cls.sharedLoadedClasses=0 java.cls.sharedUnloadedClasses=0 java.cls.unloadedClasses=0 java.property.java.class.path=".\quality-server.jar" java.property.java.home="D:\soft\jdk11"
command
(base) PS C:\Users\zishi> jcmd 8196 help 8196: The following commands are available: Compiler.CodeHeap_Analytics Compiler.codecache Compiler.codelist Compiler.directives_add Compiler.directives_clear Compiler.directives_print Compiler.directives_remove Compiler.queue GC.class_histogram GC.class_stats GC.finalizer_info GC.heap_dump GC.heap_info GC.run GC.run_finalization JFR.check JFR.configure JFR.dump JFR.start JFR.stop JVMTI.agent_load JVMTI.data_dump ManagementAgent.start ManagementAgent.start_local ManagementAgent.status ManagementAgent.stop Thread.print VM.check_commercial_features VM.class_hierarchy VM.classloader_stats VM.classloaders VM.command_line VM.dynlibs VM.flags VM.info VM.log VM.metaspace VM.native_memory VM.print_touched_methods VM.set_flag VM.stringtable VM.symboltable VM.system_properties VM.systemdictionary VM.unlock_commercial_features VM.uptime VM.version help For more information about a specific command use 'help <command>'.
(base) PS C:\Users\zishi> jcmd 8196 help help
8196:
help
For more information about a specific command use 'help <command>'. With no argument this will show a list of available commands. 'help all' will show help for all commands.
Impact: Low
Syntax: help [options] [<command name>]
Arguments:
command name : [optional] The name of the command for which we want help (STRING, no default value)
Options: (options must be specified using the <key> or <key>=<value> syntax)
-all : [optional] Show help for all commands (BOOLEAN, false)
VM part
VM.check_commercial_features
VM.class_hierarchy
VM.classloader_stats
VM.classloaders
VM.command_line
VM.dynlibs
VM.flags
VM.info
VM.log
VM.metaspace
VM.native_memory
VM.print_touched_methods
VM.set_flag
VM.stringtable
VM.symboltable
VM.system_properties
VM.systemdictionary
(base) PS C:\Users\zishi> jcmd 8196 VM.unlock_commercial_features 8196: VM.unlock_commercial_features is obsolete as it is no longer required.
(base) PS C:\Users\zishi> jcmd 8196 help VM.uptime
8196:
VM.uptime
Print VM uptime.
Impact: Low
Syntax: VM.uptime [options]
Options: (options must be specified using the <key> or <key>=<value> syntax)
-date : [optional] Add a prefix with current date (BOOLEAN, false)
(base) PS C:\Users\zishi> jcmd 8196 VM.uptime
8196:
1626.351 seconds
(base) PS C:\Users\zishi> jcmd 8196 help VM.version 8196: VM.version Print JVM version information. Impact: Low Permission: java.util.PropertyPermission(java.vm.version, read) Syntax: VM.version (base) PS C:\Users\zishi> jcmd 8196 VM.version 8196: Java HotSpot(TM) 64-Bit Server VM version 11.0.13 + 10-LTS-370 JDK 11.0.13
(base) PS C:\Users\zishi> jcmd 8196 help VM.systemdictionary
8196:
VM.systemdictionary
Prints the statistics for dictionary hashtable sizes and bucket length
Impact: Medium: Depends on Java content.
Permission: java.lang.management.ManagementPermission(monitor)
Syntax: VM.systemdictionary [options]
Options: (options must be specified using the <key> or <key>=<value> syntax)
-verbose : [optional] Dump the content of each dictionary entry for all class loaders (BOOLEAN, false)
(base) PS C:\Users\zishi> jcmd 8196 VM.systemdictionary -verbose=false (default)
(base) PS C:\Users\zishi> jcmd 8196 VM.systemdictionary -verbose=false
8196:
System Dictionary for jdk.internal.reflect.DelegatingClassLoader @4f178791 class loader statistics:
Number of buckets: 1 = 8 bytes, each 8
Number of entries: 1 = 24 bytes, each 24
Total footprint : = 32 bytes
Average bucket size: 1.000
Variance of bucket size: 0.000
Std. dev. of bucket size: 0.000
Maximum bucket size: 1
System Dictionary for jdk.internal.reflect.DelegatingClassLoader @27e91d24 class loader statistics:
Number of buckets: 1 = 8 bytes, each 8
Number of entries: 1 = 24 bytes, each 24
Total footprint : = 32 bytes
Average bucket size: 1.000
Variance of bucket size: 0.000
Std. dev. of bucket size: 0.000
Maximum bucket size: 1
(base) PS C:\Users\zishi> jcmd 8196 VM.systemdictionary -verbose=true
8196:
Dictionary for loader data: 0x0000015c253ac890 for instance a 'jdk/internal/reflect/DelegatingClassLoader'{<!-- -->0x0000000615600000}
Java dictionary (table_size=1, classes=1, resizable=false)
^ indicates that initiating loader is different from defining loader
0: jdk.internal.reflect.GeneratedMethodAccessor50, loader data: 0x0000015c253ac890 for instance a 'jdk/internal/reflect/DelegatingClassLoader'{<!-- -->0x0000000615600000}
Dictionary for loader data: 0x0000015c2ec71dc0 for instance a 'jdk/internal/reflect/DelegatingClassLoader'{<!-- -->0x0000000615600100}
Java dictionary (table_size=1, classes=1, resizable=false)
^ indicates that initiating loader is different from defining loader
0: jdk.internal.reflect.GeneratedMethodAccessor49, loader data: 0x0000015c2ec71dc0 for instance a 'jdk/internal/reflect/DelegatingClassLoader'{<!-- -->0x0000000615600100}