man > java(1)

java(1)                                      Basic Tools                                     java(1)

NAME
       java - Launches a Java application.

SYNOPSIS
           java [options] classname [args]

           java [options] -jar filename [args]

       options
           Command-line options separated by spaces. See Options.

       classname
           The name of the class to be launched.

       filename
           The name of the Java Archive (JAR) file to be called. Used only with the -jar option.

       args
           The arguments passed to the main() method separated by spaces.

DESCRIPTION
       The java command starts a Java application. It does this by starting the Java Runtime
       Environment (JRE), loading the specified class, and calling that class's main() method. The
       method must be declared public and static, it must not return any value, and it must accept a
       String array as a parameter. The method declaration has the following form:

           public static void main(String[] args)


       The java command can be used to launch a JavaFX application by loading a class that either
       has a main() method or that extends javafx.application.Application. In the latter case, the
       launcher constructs an instance of the Application class, calls its init() method, and then
       calls the start(javafx.stage.Stage) method.

       By default, the first argument that is not an option of the java command is the fully
       qualified name of the class to be called. If the -jar option is specified, its argument is
       the name of the JAR file containing class and resource files for the application. The startup
       class must be indicated by the Main-Class manifest header in its source code.

       The JRE searches for the startup class (and other classes used by the application) in three
       sets of locations: the bootstrap class path, the installed extensions, and the user’s class
       path.

       Arguments after the class file name or the JAR file name are passed to the main() method.

OPTIONS
       The java command supports a wide range of options that can be divided into the following
       categories:

       •   Standard Options

       •   Non-Standard Options

       •   Advanced Runtime Options

       •   Advanced JIT Compiler Options

       •   Advanced Serviceability Options

       •   Advanced Garbage Collection Options

       Standard options are guaranteed to be supported by all implementations of the Java Virtual
       Machine (JVM). They are used for common actions, such as checking the version of the JRE,
       setting the class path, enabling verbose output, and so on.

       Non-standard options are general purpose options that are specific to the Java HotSpot
       Virtual Machine, so they are not guaranteed to be supported by all JVM implementations, and
       are subject to change. These options start with -X.

       Advanced options are not recommended for casual use. These are developer options used for
       tuning specific areas of the Java HotSpot Virtual Machine operation that often have specific
       system requirements and may require privileged access to system configuration parameters.
       They are also not guaranteed to be supported by all JVM implementations, and are subject to
       change. Advanced options start with -XX.

       To keep track of the options that were deprecated or removed in the latest release, there is
       a section named Deprecated and Removed Options at the end of the document.

       Boolean options are used to either enable a feature that is disabled by default or disable a
       feature that is enabled by default. Such options do not require a parameter. Boolean -XX
       options are enabled using the plus sign (-XX:+OptionName) and disabled using the minus sign
       (-XX:-OptionName).

       For options that require an argument, the argument may be separated from the option name by a
       space, a colon (:), or an equal sign (=), or the argument may directly follow the option (the
       exact syntax differs for each option). If you are expected to specify the size in bytes, you
       can use no suffix, or use the suffix k or K for kilobytes (KB), m or M for megabytes (MB), g
       or G for gigabytes (GB). For example, to set the size to 8 GB, you can specify either 8g,
       8192m, 8388608k, or 8589934592 as the argument. If you are expected to specify the
       percentage, use a number from 0 to 1 (for example, specify 0.25 for 25%).

   Standard Options
       These are the most commonly used options that are supported by all implementations of the
       JVM.

       -agentlib:libname[=options]
           Loads the specified native agent library. After the library name, a comma-separated list
           of options specific to the library can be used.

           If the option -agentlib:foo is specified, then the JVM attempts to load the library named
           libfoo.so in the location specified by the LD_LIBRARY_PATH system variable (on OS X this
           variable is DYLD_LIBRARY_PATH).

           The following example shows how to load the heap profiling tool (HPROF) library and get
           sample CPU information every 20 ms, with a stack depth of 3:

               -agentlib:hprof=cpu=samples,interval=20,depth=3

           The following example shows how to load the Java Debug Wire Protocol (JDWP) library and
           listen for the socket connection on port 8000, suspending the JVM before the main class
           loads:

               -agentlib:jdwp=transport=dt_socket,server=y,address=8000

           For more information about the native agent libraries, refer to the following:

           •   The java.lang.instrument package description at
               http://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html

           •   Agent Command Line Options in the JVM Tools Interface guide at
               http://docs.oracle.com/javase/8/docs/platform/jvmti/jvmti.html#starting

       -agentpath:pathname[=options]
           Loads the native agent library specified by the absolute path name. This option is
           equivalent to -agentlib but uses the full path and file name of the library.

       -client
           Selects the Java HotSpot Client VM. The 64-bit version of the Java SE Development Kit
           (JDK) currently ignores this option and instead uses the Server JVM.

           For default JVM selection, see Server-Class Machine Detection at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/server-class.html

       -Dproperty=value
           Sets a system property value. The property variable is a string with no spaces that
           represents the name of the property. The value variable is a string that represents the
           value of the property. If value is a string with spaces, then enclose it in quotation
           marks (for example -Dfoo="foo bar").

       -d32
           Runs the application in a 32-bit environment. If a 32-bit environment is not installed or
           is not supported, then an error will be reported. By default, the application is run in a
           32-bit environment unless a 64-bit system is used.

       -d64
           Runs the application in a 64-bit environment. If a 64-bit environment is not installed or
           is not supported, then an error will be reported. By default, the application is run in a
           32-bit environment unless a 64-bit system is used.

           Currently only the Java HotSpot Server VM supports 64-bit operation, and the -server
           option is implicit with the use of -d64. The -client option is ignored with the use of
           -d64. This is subject to change in a future release.

       -disableassertions[:[packagename]...|:classname]
       -da[:[packagename]...|:classname]
           Disables assertions. By default, assertions are disabled in all packages and classes.

           With no arguments, -disableassertions (-da) disables assertions in all packages and
           classes. With the packagename argument ending in ..., the switch disables assertions in
           the specified package and any subpackages. If the argument is simply ..., then the switch
           disables assertions in the unnamed package in the current working directory. With the
           classname argument, the switch disables assertions in the specified class.

           The -disableassertions (-da) option applies to all class loaders and to system classes
           (which do not have a class loader). There is one exception to this rule: if the option is
           provided with no arguments, then it does not apply to system classes. This makes it easy
           to disable assertions in all classes except for system classes. The
           -disablesystemassertions option enables you to disable assertions in all system classes.

           To explicitly enable assertions in specific packages or classes, use the
           -enableassertions (-ea) option. Both options can be used at the same time. For example,
           to run the MyClass application with assertions enabled in package com.wombat.fruitbat
           (and any subpackages) but disabled in class com.wombat.fruitbat.Brickbat, use the
           following command:

               java -ea:com.wombat.fruitbat... -da:com.wombat.fruitbat.Brickbat MyClass


       -disablesystemassertions
       -dsa
           Disables assertions in all system classes.

       -enableassertions[:[packagename]...|:classname]
       -ea[:[packagename]...|:classname]
           Enables assertions. By default, assertions are disabled in all packages and classes.

           With no arguments, -enableassertions (-ea) enables assertions in all packages and
           classes. With the packagename argument ending in ..., the switch enables assertions in
           the specified package and any subpackages. If the argument is simply ..., then the switch
           enables assertions in the unnamed package in the current working directory. With the
           classname argument, the switch enables assertions in the specified class.

           The -enableassertions (-ea) option applies to all class loaders and to system classes
           (which do not have a class loader). There is one exception to this rule: if the option is
           provided with no arguments, then it does not apply to system classes. This makes it easy
           to enable assertions in all classes except for system classes. The
           -enablesystemassertions option provides a separate switch to enable assertions in all
           system classes.

           To explicitly disable assertions in specific packages or classes, use the
           -disableassertions (-da) option. If a single command contains multiple instances of these
           switches, then they are processed in order before loading any classes. For example, to
           run the MyClass application with assertions enabled only in package com.wombat.fruitbat
           (and any subpackages) but disabled in class com.wombat.fruitbat.Brickbat, use the
           following command:

               java -ea:com.wombat.fruitbat... -da:com.wombat.fruitbat.Brickbat MyClass


       -enablesystemassertions
       -esa
           Enables assertions in all system classes.

       -help
       -?
           Displays usage information for the java command without actually running the JVM.

       -jar filename
           Executes a program encapsulated in a JAR file. The filename argument is the name of a JAR
           file with a manifest that contains a line in the form Main-Class:classname that defines
           the class with the public static void main(String[] args) method that serves as your
           application's starting point.

           When you use the -jar option, the specified JAR file is the source of all user classes,
           and other class path settings are ignored.

           For more information about JAR files, see the following resources:

           •   jar(1)

           •   The Java Archive (JAR) Files guide at
               http://docs.oracle.com/javase/8/docs/technotes/guides/jar/index.html

           •   Lesson: Packaging Programs in JAR Files at

               http://docs.oracle.com/javase/tutorial/deployment/jar/index.html

       -javaagent:jarpath[=options]
           Loads the specified Java programming language agent. For more information about
           instrumenting Java applications, see the java.lang.instrument package description in the
           Java API documentation at
           http://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html

       -jre-restrict-search
           Includes user-private JREs in the version search.

       -no-jre-restrict-search
           Excludes user-private JREs from the version search.

       -server
           Selects the Java HotSpot Server VM. The 64-bit version of the JDK supports only the
           Server VM, so in that case the option is implicit.

           For default JVM selection, see Server-Class Machine Detection at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/server-class.html

       -showversion
           Displays version information and continues execution of the application. This option is
           equivalent to the -version option except that the latter instructs the JVM to exit after
           displaying version information.

       -splash:imgname
           Shows the splash screen with the image specified by imgname. For example, to show the
           splash.gif file from the images directory when starting your application, use the
           following option:

               -splash:images/splash.gif


       -verbose:class
           Displays information about each loaded class.

       -verbose:gc
           Displays information about each garbage collection (GC) event.

       -verbose:jni
           Displays information about the use of native methods and other Java Native Interface
           (JNI) activity.

       -version
           Displays version information and then exits. This option is equivalent to the
           -showversion option except that the latter does not instruct the JVM to exit after
           displaying version information.

       -version:release
           Specifies the release version to be used for running the application. If the version of
           the java command called does not meet this specification and an appropriate
           implementation is found on the system, then the appropriate implementation will be used.

           The release argument specifies either the exact version string, or a list of version
           strings and ranges separated by spaces. A version string is the developer designation of
           the version number in the following form: 1.x.0_u (where x is the major version number,
           and u is the update version number). A version range is made up of a version string
           followed by a plus sign (+) to designate this version or later, or a part of a version
           string followed by an asterisk (*) to designate any version string with a matching
           prefix. Version strings and ranges can be combined using a space for a logical OR
           combination, or an ampersand (&) for a logical AND combination of two version
           strings/ranges. For example, if running the class or JAR file requires either JRE 6u13
           (1.6.0_13), or any JRE 6 starting from 6u10 (1.6.0_10), specify the following:

               -version:"1.6.0_13 1.6* & 1.6.0_10+"

           Quotation marks are necessary only if there are spaces in the release parameter.

           For JAR files, the preference is to specify version requirements in the JAR file manifest
           rather than on the command line.

   Non-Standard Options
       These options are general purpose options that are specific to the Java HotSpot Virtual
       Machine.

       -X
           Displays help for all available -X options.

       -Xbatch
           Disables background compilation. By default, the JVM compiles the method as a background
           task, running the method in interpreter mode until the background compilation is
           finished. The -Xbatch flag disables background compilation so that compilation of all
           methods proceeds as a foreground task until completed.

           This option is equivalent to -XX:-BackgroundCompilation.

       -Xbootclasspath:path
           Specifies a list of directories, JAR files, and ZIP archives separated by colons (:) to
           search for boot class files. These are used in place of the boot class files included in
           the JDK.

           Do not deploy applications that use this option to override a class in rt.jar, because
           this violates the JRE binary code license.

       -Xbootclasspath/a:path
           Specifies a list of directories, JAR files, and ZIP archives separated by colons (:) to
           append to the end of the default bootstrap class path.

           Do not deploy applications that use this option to override a class in rt.jar, because
           this violates the JRE binary code license.

       -Xbootclasspath/p:path
           Specifies a list of directories, JAR files, and ZIP archives separated by colons (:) to
           prepend to the front of the default bootstrap class path.

           Do not deploy applications that use this option to override a class in rt.jar, because
           this violates the JRE binary code license.

       -Xcheck:jni
           Performs additional checks for Java Native Interface (JNI) functions. Specifically, it
           validates the parameters passed to the JNI function and the runtime environment data
           before processing the JNI request. Any invalid data encountered indicates a problem in
           the native code, and the JVM will terminate with an irrecoverable error in such cases.
           Expect a performance degradation when this option is used.

       -Xcomp
           Forces compilation of methods on first invocation. By default, the Client VM (-client)
           performs 1,000 interpreted method invocations and the Server VM (-server) performs 10,000
           interpreted method invocations to gather information for efficient compilation.
           Specifying the -Xcomp option disables interpreted method invocations to increase
           compilation performance at the expense of efficiency.

           You can also change the number of interpreted method invocations before compilation using
           the -XX:CompileThreshold option.

       -Xdebug
           Does nothing. Provided for backward compatibility.

       -Xdiag
           Shows additional diagnostic messages.

       -Xfuture
           Enables strict class-file format checks that enforce close conformance to the class-file
           format specification. Developers are encouraged to use this flag when developing new code
           because the stricter checks will become the default in future releases.

       -Xint
           Runs the application in interpreted-only mode. Compilation to native code is disabled,
           and all bytecode is executed by the interpreter. The performance benefits offered by the
           just in time (JIT) compiler are not present in this mode.

       -Xinternalversion
           Displays more detailed JVM version information than the -version option, and then exits.

       -Xloggc:filename
           Sets the file to which verbose GC events information should be redirected for logging.
           The information written to this file is similar to the output of -verbose:gc with the
           time elapsed since the first GC event preceding each logged event. The -Xloggc option
           overrides -verbose:gc if both are given with the same java command.

           Example:

               -Xloggc:garbage-collection.log


       -Xmaxjitcodesize=size
           Specifies the maximum code cache size (in bytes) for JIT-compiled code. Append the letter
           k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes.
           The default maximum code cache size is 240 MB; if you disable tiered compilation with the
           option -XX:-TieredCompilation, then the default size is 48 MB:

               -Xmaxjitcodesize=240m

           This option is equivalent to -XX:ReservedCodeCacheSize.

       -Xmixed
           Executes all bytecode by the interpreter except for hot methods, which are compiled to
           native code.

       -Xmnsize
           Sets the initial and maximum size (in bytes) of the heap for the young generation
           (nursery). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes,
           g or G to indicate gigabytes.

           The young generation region of the heap is used for new objects. GC is performed in this
           region more often than in other regions. If the size for the young generation is too
           small, then a lot of minor garbage collections will be performed. If the size is too
           large, then only full garbage collections will be performed, which can take a long time
           to complete. Oracle recommends that you keep the size for the young generation between a
           half and a quarter of the overall heap size.

           The following examples show how to set the initial and maximum size of young generation
           to 256 MB using various units:

               -Xmn256m
               -Xmn262144k
               -Xmn268435456

           Instead of the -Xmn option to set both the initial and maximum size of the heap for the
           young generation, you can use -XX:NewSize to set the initial size and -XX:MaxNewSize to
           set the maximum size.

       -Xmssize
           Sets the initial size (in bytes) of the heap. This value must be a multiple of 1024 and
           greater than 1 MB. Append the letter k or K to indicate kilobytes, m or M to indicate
           megabytes, g or G to indicate gigabytes.

           The following examples show how to set the size of allocated memory to 6 MB using various
           units:

               -Xms6291456
               -Xms6144k
               -Xms6m

           If you do not set this option, then the initial size will be set as the sum of the sizes
           allocated for the old generation and the young generation. The initial size of the heap
           for the young generation can be set using the -Xmn option or the -XX:NewSize option.

       -Xmxsize
           Specifies the maximum size (in bytes) of the memory allocation pool in bytes. This value
           must be a multiple of 1024 and greater than 2 MB. Append the letter k or K to indicate
           kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value
           is chosen at runtime based on system configuration. For server deployments, -Xms and -Xmx
           are often set to the same value. See the section "Ergonomics" in Java SE HotSpot Virtual
           Machine Garbage Collection Tuning Guide at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/index.html.

           The following examples show how to set the maximum allowed size of allocated memory to 80
           MB using various units:

               -Xmx83886080
               -Xmx81920k
               -Xmx80m

           The -Xmx option is equivalent to -XX:MaxHeapSize.

       -Xnoclassgc
           Disables garbage collection (GC) of classes. This can save some GC time, which shortens
           interruptions during the application run.

           When you specify -Xnoclassgc at startup, the class objects in the application will be
           left untouched during GC and will always be considered live. This can result in more
           memory being permanently occupied which, if not used carefully, will throw an out of
           memory exception.

       -Xprof
           Profiles the running program and sends profiling data to standard output. This option is
           provided as a utility that is useful in program development and is not intended to be
           used in production systems.

       -Xrs
           Reduces the use of operating system signals by the JVM.

           Shutdown hooks enable orderly shutdown of a Java application by running user cleanup code
           (such as closing database connections) at shutdown, even if the JVM terminates abruptly.

           The JVM catches signals to implement shutdown hooks for unexpected termination. The JVM
           uses SIGHUP, SIGINT, and SIGTERM to initiate the running of shutdown hooks.

           The JVM uses a similar mechanism to implement the feature of dumping thread stacks for
           debugging purposes. The JVM uses SIGQUIT to perform thread dumps.

           Applications embedding the JVM frequently need to trap signals such as SIGINT or SIGTERM,
           which can lead to interference with the JVM signal handlers. The -Xrs option is available
           to address this issue. When -Xrs is used, the signal masks for SIGINT, SIGTERM, SIGHUP,
           and SIGQUIT are not changed by the JVM, and signal handlers for these signals are not
           installed.

           There are two consequences of specifying -Xrs:

           •   SIGQUIT thread dumps are not available.

           •   User code is responsible for causing shutdown hooks to run, for example, by calling
               System.exit() when the JVM is to be terminated.

       -Xshare:mode
           Sets the class data sharing (CDS) mode. Possible mode arguments for this option include
           the following:

           auto
               Use CDS if possible. This is the default value for Java HotSpot 32-Bit Client VM.

           on
               Require the use of CDS. Print an error message and exit if class data sharing cannot
               be used.

           off
               Do not use CDS. This is the default value for Java HotSpot 32-Bit Server VM, Java
               HotSpot 64-Bit Client VM, and Java HotSpot 64-Bit Server VM.

           dump
               Manually generate the CDS archive. Specify the application class path as described in
               "Setting the Class Path ".

               You should regenerate the CDS archive with each new JDK release.

       -XshowSettings:category
           Shows settings and continues. Possible category arguments for this option include the
           following:

           all
               Shows all categories of settings. This is the default value.

           locale
               Shows settings related to locale.

           properties
               Shows settings related to system properties.

           vm
               Shows the settings of the JVM.

       -Xsssize
           Sets the thread stack size (in bytes). Append the letter k or K to indicate KB, m or M to
           indicate MB, g or G to indicate GB. The default value depends on the platform:

           •   Linux/ARM (32-bit): 320 KB

           •   Linux/i386 (32-bit): 320 KB

           •   Linux/x64 (64-bit): 1024 KB

           •   OS X (64-bit): 1024 KB

           •   Oracle Solaris/i386 (32-bit): 320 KB

           •   Oracle Solaris/x64 (64-bit): 1024 KB

           The following examples set the thread stack size to 1024 KB in different units:

               -Xss1m
               -Xss1024k
               -Xss1048576

           This option is equivalent to -XX:ThreadStackSize.

       -Xusealtsigs
           Use alternative signals instead of SIGUSR1 and SIGUSR2 for JVM internal signals. This
           option is equivalent to -XX:+UseAltSigs.

       -Xverify:mode
           Sets the mode of the bytecode verifier. Bytecode verification helps to troubleshoot some
           problems, but it also adds overhead to the running application. Possible mode arguments
           for this option include the following:

           none
               Do not verify the bytecode. This reduces startup time and also reduces the protection
               provided by Java.

           remote
               Verify those classes that are not loaded by the bootstrap class loader. This is the
               default behavior if you do not specify the -Xverify option.

           all
               Verify all classes.

   Advanced Runtime Options
       These options control the runtime behavior of the Java HotSpot VM.

       -XX:+CheckEndorsedAndExtDirs
           Enables the option to prevent the java command from running a Java application if it uses
           the endorsed-standards override mechanism or the extension mechanism. This option checks
           if an application is using one of these mechanisms by checking the following:

           •   The java.ext.dirs or java.endorsed.dirs system property is set.

           •   The lib/endorsed directory exists and is not empty.

           •   The lib/ext directory contains any JAR files other than those of the JDK.

           •   The system-wide platform-specific extension directory contains any JAR files.

       -XX:+DisableAttachMechanism
           Enables the option that disables the mechanism that lets tools attach to the JVM. By
           default, this option is disabled, meaning that the attach mechanism is enabled and you
           can use tools such as jcmd, jstack, jmap, and jinfo.

       -XX:ErrorFile=filename
           Specifies the path and file name to which error data is written when an irrecoverable
           error occurs. By default, this file is created in the current working directory and named
           hs_err_pidpid.log where pid is the identifier of the process that caused the error. The
           following example shows how to set the default log file (note that the identifier of the
           process is specified as %p):

               -XX:ErrorFile=./hs_err_pid%p.log

           The following example shows how to set the error log to /var/log/java/java_error.log:

               -XX:ErrorFile=/var/log/java/java_error.log

           If the file cannot be created in the specified directory (due to insufficient space,
           permission problem, or another issue), then the file is created in the temporary
           directory for the operating system. The temporary directory is /tmp.

       -XX:+FailOverToOldVerifier
           Enables automatic failover to the old verifier when the new type checker fails. By
           default, this option is disabled and it is ignored (that is, treated as disabled) for
           classes with a recent bytecode version. You can enable it for classes with older versions
           of the bytecode.

       -XX:LargePageSizeInBytes=size
           On Solaris, sets the maximum size (in bytes) for large pages used for Java heap. The size
           argument must be a power of 2 (2, 4, 8, 16, ...). Append the letter k or K to indicate
           kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. By default, the
           size is set to 0, meaning that the JVM chooses the size for large pages automatically.

           The following example illustrates how to set the large page size to 4 megabytes (MB):

               -XX:LargePageSizeInBytes=4m


       -XX:MaxDirectMemorySize=size
           Sets the maximum total size (in bytes) of the New I/O (the java.nio package)
           direct-buffer allocations. Append the letter k or K to indicate kilobytes, m or M to
           indicate megabytes, g or G to indicate gigabytes. By default, the size is set to 0,
           meaning that the JVM chooses the size for NIO direct-buffer allocations automatically.

           The following examples illustrate how to set the NIO size to 1024 KB in different units:

               -XX:MaxDirectMemorySize=1m
               -XX:MaxDirectMemorySize=1024k
               -XX:MaxDirectMemorySize=1048576


       -XX:NativeMemoryTracking=mode
           Specifies the mode for tracking JVM native memory usage. Possible mode arguments for this
           option include the following:

           off
               Do not track JVM native memory usage. This is the default behavior if you do not
               specify the -XX:NativeMemoryTracking option.

           summary
               Only track memory usage by JVM subsystems, such as Java heap, class, code, and
               thread.

           detail
               In addition to tracking memory usage by JVM subsystems, track memory usage by
               individual CallSite, individual virtual memory region and its committed regions.

       -XX:ObjectAlignmentInBytes=alignment
           Sets the memory alignment of Java objects (in bytes). By default, the value is set to 8
           bytes. The specified value should be a power of two, and must be within the range of 8
           and 256 (inclusive). This option makes it possible to use compressed pointers with large
           Java heap sizes.

           The heap size limit in bytes is calculated as:

           4GB * ObjectAlignmentInBytes

           Note: As the alignment value increases, the unused space between objects will also
           increase. As a result, you may not realize any benefits from using compressed pointers
           with large Java heap sizes.

       -XX:OnError=string
           Sets a custom command or a series of semicolon-separated commands to run when an
           irrecoverable error occurs. If the string contains spaces, then it must be enclosed in
           quotation marks.

           The following example shows how the -XX:OnError option can be used to run the gcore
           command to create the core image, and the debugger is started to attach to the process in
           case of an irrecoverable error (the %p designates the current process):

               -XX:OnError="gcore %p;dbx - %p"


       -XX:OnOutOfMemoryError=string
           Sets a custom command or a series of semicolon-separated commands to run when an
           OutOfMemoryError exception is first thrown. If the string contains spaces, then it must
           be enclosed in quotation marks. For an example of a command string, see the description
           of the -XX:OnError option.

       -XX:+PerfDataSaveToFile
           If enabled, saves jstat(1) binary data when the Java application exits. This binary data
           is saved in a file named hsperfdata_<pid>, where <pid> is the process identifier of the
           Java application you ran. Use jstat to display the performance data contained in this
           file as follows:

               jstat -class file:///<path>/hsperfdata_<pid>
               jstat -gc file:///<path>/hsperfdata_<pid>

       -XX:+PrintCommandLineFlags
           Enables printing of ergonomically selected JVM flags that appeared on the command line.
           It can be useful to know the ergonomic values set by the JVM, such as the heap space size
           and the selected garbage collector. By default, this option is disabled and flags are not
           printed.

       -XX:+PrintNMTStatistics
           Enables printing of collected native memory tracking data at JVM exit when native memory
           tracking is enabled (see -XX:NativeMemoryTracking). By default, this option is disabled
           and native memory tracking data is not printed.

       -XX:+RelaxAccessControlCheck
           Decreases the amount of access control checks in the verifier. By default, this option is
           disabled, and it is ignored (that is, treated as disabled) for classes with a recent
           bytecode version. You can enable it for classes with older versions of the bytecode.

       -XX:+ShowMessageBoxOnError
           Enables displaying of a dialog box when the JVM experiences an irrecoverable error. This
           prevents the JVM from exiting and keeps the process active so that you can attach a
           debugger to it to investigate the cause of the error. By default, this option is
           disabled.

       -XX:ThreadStackSize=size
           Sets the thread stack size (in bytes). Append the letter k or K to indicate kilobytes, m
           or M to indicate megabytes, g or G to indicate gigabytes. The default value depends on
           the platform:

           •   Linux/ARM (32-bit): 320 KB

           •   Linux/i386 (32-bit): 320 KB

           •   Linux/x64 (64-bit): 1024 KB

           •   OS X (64-bit): 1024 KB

           •   Oracle Solaris/i386 (32-bit): 320 KB

           •   Oracle Solaris/x64 (64-bit): 1024 KB

           The following examples show how to set the thread stack size to 1024 KB in different
           units:

               -XX:ThreadStackSize=1m
               -XX:ThreadStackSize=1024k
               -XX:ThreadStackSize=1048576

           This option is equivalent to -Xss.

       -XX:+TraceClassLoading
           Enables tracing of classes as they are loaded. By default, this option is disabled and
           classes are not traced.

       -XX:+TraceClassLoadingPreorder
           Enables tracing of all loaded classes in the order in which they are referenced. By
           default, this option is disabled and classes are not traced.

       -XX:+TraceClassResolution
           Enables tracing of constant pool resolutions. By default, this option is disabled and
           constant pool resolutions are not traced.

       -XX:+TraceClassUnloading
           Enables tracing of classes as they are unloaded. By default, this option is disabled and
           classes are not traced.

       -XX:+TraceLoaderConstraints
           Enables tracing of the loader constraints recording. By default, this option is disabled
           and loader constraints recording is not traced.

       -XX:+UseAltSigs
           Enables the use of alternative signals instead of SIGUSR1 and SIGUSR2 for JVM internal
           signals. By default, this option is disabled and alternative signals are not used. This
           option is equivalent to -Xusealtsigs.

       -XX:-UseBiasedLocking
           Disables the use of biased locking. Some applications with significant amounts of
           uncontended synchronization may attain significant speedups with this flag enabled,
           whereas applications with certain patterns of locking may see slowdowns. For more
           information about the biased locking technique, see the example in Java Tuning White
           Paper at http://www.oracle.com/technetwork/java/tuning-139912.html#section4.2.5

           By default, this option is enabled.

       -XX:-UseCompressedOops
           Disables the use of compressed pointers. By default, this option is enabled, and
           compressed pointers are used when Java heap sizes are less than 32 GB. When this option
           is enabled, object references are represented as 32-bit offsets instead of 64-bit
           pointers, which typically increases performance when running the application with Java
           heap sizes less than 32 GB. This option works only for 64-bit JVMs.

           It is also possible to use compressed pointers when Java heap sizes are greater than
           32GB. See the -XX:ObjectAlignmentInBytes option.

       -XX:+UseHugeTLBFS
           This option for Linux is the equivalent of specifying -XX:+UseLargePages. This option is
           disabled by default. This option pre-allocates all large pages up-front, when memory is
           reserved; consequently the JVM cannot dynamically grow or shrink large pages memory
           areas; see -XX:UseTransparentHugePages if you want this behavior.

           For more information, see "Large Pages".

       -XX:+UseLargePages
           Enables the use of large page memory. By default, this option is disabled and large page
           memory is not used.

           For more information, see "Large Pages".

       -XX:+UseMembar
           Enables issuing of membars on thread state transitions. This option is disabled by
           default on all platforms except ARM servers, where it is enabled. (It is recommended that
           you do not disable this option on ARM servers.)

       -XX:+UsePerfData
           Enables the perfdata feature. This option is enabled by default to allow JVM monitoring
           and performance testing. Disabling it suppresses the creation of the hsperfdata_userid
           directories. To disable the perfdata feature, specify -XX:-UsePerfData.

       -XX:+UseTransparentHugePages
           On Linux, enables the use of large pages that can dynamically grow or shrink. This option
           is disabled by default. You may encounter performance problems with transparent huge
           pages as the OS moves other pages around to create huge pages; this option is made
           available for experimentation.

           For more information, see "Large Pages".

       -XX:+AllowUserSignalHandlers
           Enables installation of signal handlers by the application. By default, this option is
           disabled and the application is not allowed to install signal handlers.

   Advanced JIT Compiler Options
       These options control the dynamic just-in-time (JIT) compilation performed by the Java
       HotSpot VM.

       -XX:+AggressiveOpts
           Enables the use of aggressive performance optimization features, which are expected to
           become default in upcoming releases. By default, this option is disabled and experimental
           performance features are not used.

       -XX:AllocateInstancePrefetchLines=lines
           Sets the number of lines to prefetch ahead of the instance allocation pointer. By
           default, the number of lines to prefetch is set to 1:

               -XX:AllocateInstancePrefetchLines=1

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchDistance=size
           Sets the size (in bytes) of the prefetch distance for object allocation. Memory about to
           be written with the value of new objects is prefetched up to this distance starting from
           the address of the last allocated object. Each Java thread has its own allocation point.

           Negative values denote that prefetch distance is chosen based on the platform. Positive
           values are bytes to prefetch. Append the letter k or K to indicate kilobytes, m or M to
           indicate megabytes, g or G to indicate gigabytes. The default value is set to -1.

           The following example shows how to set the prefetch distance to 1024 bytes:

               -XX:AllocatePrefetchDistance=1024

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchInstr=instruction
           Sets the prefetch instruction to prefetch ahead of the allocation pointer. Only the Java
           HotSpot Server VM supports this option. Possible values are from 0 to 3. The actual
           instructions behind the values depend on the platform. By default, the prefetch
           instruction is set to 0:

               -XX:AllocatePrefetchInstr=0

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchLines=lines
           Sets the number of cache lines to load after the last object allocation by using the
           prefetch instructions generated in compiled code. The default value is 1 if the last
           allocated object was an instance, and 3 if it was an array.

           The following example shows how to set the number of loaded cache lines to 5:

               -XX:AllocatePrefetchLines=5

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchStepSize=size
           Sets the step size (in bytes) for sequential prefetch instructions. Append the letter k
           or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes.
           By default, the step size is set to 16 bytes:

               -XX:AllocatePrefetchStepSize=16

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchStyle=style
           Sets the generated code style for prefetch instructions. The style argument is an integer
           from 0 to 3:

           0
               Do not generate prefetch instructions.

           1
               Execute prefetch instructions after each allocation. This is the default parameter.

           2
               Use the thread-local allocation block (TLAB) watermark pointer to determine when
               prefetch instructions are executed.

           3
               Use BIS instruction on SPARC for allocation prefetch.

           Only the Java HotSpot Server VM supports this option.

       -XX:+BackgroundCompilation
           Enables background compilation. This option is enabled by default. To disable background
           compilation, specify -XX:-BackgroundCompilation (this is equivalent to specifying
           -Xbatch).

       -XX:CICompilerCount=threads
           Sets the number of compiler threads to use for compilation. By default, the number of
           threads is set to 2 for the server JVM, to 1 for the client JVM, and it scales to the
           number of cores if tiered compilation is used. The following example shows how to set the
           number of threads to 2:

               -XX:CICompilerCount=2


       -XX:CodeCacheMinimumFreeSpace=size
           Sets the minimum free space (in bytes) required for compilation. Append the letter k or K
           to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. When
           less than the minimum free space remains, compiling stops. By default, this option is set
           to 500 KB. The following example shows how to set the minimum free space to 1024 MB:

               -XX:CodeCacheMinimumFreeSpace=1024m


       -XX:CompileCommand=command,method[,option]
           Specifies a command to perform on a method. For example, to exclude the indexOf() method
           of the String class from being compiled, use the following:

               -XX:CompileCommand=exclude,java/lang/String.indexOf

           Note that the full class name is specified, including all packages and subpackages
           separated by a slash (/). For easier cut and paste operations, it is also possible to use
           the method name format produced by the -XX:+PrintCompilation and -XX:+LogCompilation
           options:

               -XX:CompileCommand=exclude,java.lang.String::indexOf

           If the method is specified without the signature, the command will be applied to all
           methods with the specified name. However, you can also specify the signature of the
           method in the class file format. In this case, you should enclose the arguments in
           quotation marks, because otherwise the shell treats the semicolon as command end. For
           example, if you want to exclude only the indexOf(String) method of the String class from
           being compiled, use the following:

               -XX:CompileCommand="exclude,java/lang/String.indexOf,(Ljava/lang/String;)I"

           You can also use the asterisk (*) as a wildcard for class and method names. For example,
           to exclude all indexOf() methods in all classes from being compiled, use the following:

               -XX:CompileCommand=exclude,*.indexOf

           The commas and periods are aliases for spaces, making it easier to pass compiler commands
           through a shell. You can pass arguments to -XX:CompileCommand using spaces as separators
           by enclosing the argument in quotation marks:

               -XX:CompileCommand="exclude java/lang/String indexOf"

           Note that after parsing the commands passed on the command line using the
           -XX:CompileCommand options, the JIT compiler then reads commands from the
           .hotspot_compiler file. You can add commands to this file or specify a different file
           using the -XX:CompileCommandFile option.

           To add several commands, either specify the -XX:CompileCommand option multiple times, or
           separate each argument with the newline separator (\n). The following commands are
           available:

           break
               Set a breakpoint when debugging the JVM to stop at the beginning of compilation of
               the specified method.

           compileonly
               Exclude all methods from compilation except for the specified method. As an
               alternative, you can use the -XX:CompileOnly option, which allows to specify several
               methods.

           dontinline
               Prevent inlining of the specified method.

           exclude
               Exclude the specified method from compilation.

           help
               Print a help message for the -XX:CompileCommand option.

           inline
               Attempt to inline the specified method.

           log
               Exclude compilation logging (with the -XX:+LogCompilation option) for all methods
               except for the specified method. By default, logging is performed for all compiled
               methods.

           option
               This command can be used to pass a JIT compilation option to the specified method in
               place of the last argument (option). The compilation option is set at the end, after
               the method name. For example, to enable the BlockLayoutByFrequency option for the
               append() method of the StringBuffer class, use the following:

                   -XX:CompileCommand=option,java/lang/StringBuffer.append,BlockLayoutByFrequency

               You can specify multiple compilation options, separated by commas or spaces.

           print
               Print generated assembler code after compilation of the specified method.

           quiet
               Do not print the compile commands. By default, the commands that you specify with the
               -XX:CompileCommand option are printed; for example, if you exclude from compilation
               the indexOf() method of the String class, then the following will be printed to
               standard output:

                   CompilerOracle: exclude java/lang/String.indexOf

               You can suppress this by specifying the -XX:CompileCommand=quiet option before other
               -XX:CompileCommand options.

       -XX:CompileCommandFile=filename
           Sets the file from which JIT compiler commands are read. By default, the
           .hotspot_compiler file is used to store commands performed by the JIT compiler.

           Each line in the command file represents a command, a class name, and a method name for
           which the command is used. For example, this line prints assembly code for the toString()
           method of the String class:

               print java/lang/String toString

           For more information about specifying the commands for the JIT compiler to perform on
           methods, see the -XX:CompileCommand option.

       -XX:CompileOnly=methods
           Sets the list of methods (separated by commas) to which compilation should be restricted.
           Only the specified methods will be compiled. Specify each method with the full class name
           (including the packages and subpackages). For example, to compile only the length()
           method of the String class and the size() method of the List class, use the following:

               -XX:CompileOnly=java/lang/String.length,java/util/List.size

           Note that the full class name is specified, including all packages and subpackages
           separated by a slash (/). For easier cut and paste operations, it is also possible to use
           the method name format produced by the -XX:+PrintCompilation and -XX:+LogCompilation
           options:

               -XX:CompileOnly=java.lang.String::length,java.util.List::size

           Although wildcards are not supported, you can specify only the class or package name to
           compile all methods in that class or package, as well as specify just the method to
           compile methods with this name in any class:

               -XX:CompileOnly=java/lang/String
               -XX:CompileOnly=java/lang
               -XX:CompileOnly=.length


       -XX:CompileThreshold=invocations
           Sets the number of interpreted method invocations before compilation. By default, in the
           server JVM, the JIT compiler performs 10,000 interpreted method invocations to gather
           information for efficient compilation. For the client JVM, the default setting is 1,500
           invocations. This option is ignored when tiered compilation is enabled; see the option
           -XX:+TieredCompilation. The following example shows how to set the number of interpreted
           method invocations to 5,000:

               -XX:CompileThreshold=5000

           You can completely disable interpretation of Java methods before compilation by
           specifying the -Xcomp option.

       -XX:+DoEscapeAnalysis
           Enables the use of escape analysis. This option is enabled by default. To disable the use
           of escape analysis, specify -XX:-DoEscapeAnalysis. Only the Java HotSpot Server VM
           supports this option.

       -XX:InitialCodeCacheSize=size
           Sets the initial code cache size (in bytes). Append the letter k or K to indicate
           kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value
           is set to 500 KB. The initial code cache size should be not less than the system's
           minimal memory page size. The following example shows how to set the initial code cache
           size to 32 KB:

               -XX:InitialCodeCacheSize=32k


       -XX:+Inline
           Enables method inlining. This option is enabled by default to increase performance. To
           disable method inlining, specify -XX:-Inline.

       -XX:InlineSmallCode=size
           Sets the maximum code size (in bytes) for compiled methods that should be inlined. Append
           the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate
           gigabytes. Only compiled methods with the size smaller than the specified size will be
           inlined. By default, the maximum code size is set to 1000 bytes:

               -XX:InlineSmallCode=1000


       -XX:+LogCompilation
           Enables logging of compilation activity to a file named hotspot.log in the current
           working directory. You can specify a different log file path and name using the
           -XX:LogFile option.

           By default, this option is disabled and compilation activity is not logged. The
           -XX:+LogCompilation option has to be used together with the -XX:UnlockDiagnosticVMOptions
           option that unlocks diagnostic JVM options.

           You can enable verbose diagnostic output with a message printed to the console every time
           a method is compiled by using the -XX:+PrintCompilation option.

       -XX:MaxInlineSize=size
           Sets the maximum bytecode size (in bytes) of a method to be inlined. Append the letter k
           or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes.
           By default, the maximum bytecode size is set to 35 bytes:

               -XX:MaxInlineSize=35


       -XX:MaxNodeLimit=nodes
           Sets the maximum number of nodes to be used during single method compilation. By default,
           the maximum number of nodes is set to 65,000:

               -XX:MaxNodeLimit=65000


       -XX:MaxTrivialSize=size
           Sets the maximum bytecode size (in bytes) of a trivial method to be inlined. Append the
           letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate
           gigabytes. By default, the maximum bytecode size of a trivial method is set to 6 bytes:

               -XX:MaxTrivialSize=6


       -XX:+OptimizeStringConcat
           Enables the optimization of String concatenation operations. This option is enabled by
           default. To disable the optimization of String concatenation operations, specify
           -XX:-OptimizeStringConcat. Only the Java HotSpot Server VM supports this option.

       -XX:+PrintAssembly
           Enables printing of assembly code for bytecoded and native methods by using the external
           disassembler.so library. This enables you to see the generated code, which may help you
           to diagnose performance issues.

           By default, this option is disabled and assembly code is not printed. The
           -XX:+PrintAssembly option has to be used together with the -XX:UnlockDiagnosticVMOptions
           option that unlocks diagnostic JVM options.

       -XX:+PrintCompilation
           Enables verbose diagnostic output from the JVM by printing a message to the console every
           time a method is compiled. This enables you to see which methods actually get compiled.
           By default, this option is disabled and diagnostic output is not printed.

           You can also log compilation activity to a file by using the -XX:+LogCompilation option.

       -XX:+PrintInlining
           Enables printing of inlining decisions. This enables you to see which methods are getting
           inlined.

           By default, this option is disabled and inlining information is not printed. The
           -XX:+PrintInlining option has to be used together with the -XX:+UnlockDiagnosticVMOptions
           option that unlocks diagnostic JVM options.

       -XX:ReservedCodeCacheSize=size
           Sets the maximum code cache size (in bytes) for JIT-compiled code. Append the letter k or
           K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The
           default maximum code cache size is 240 MB; if you disable tiered compilation with the
           option -XX:-TieredCompilation, then the default size is 48 MB. This option has a limit of
           2 GB; otherwise, an error is generated. The maximum code cache size should not be less
           than the initial code cache size; see the option -XX:InitialCodeCacheSize. This option is
           equivalent to -Xmaxjitcodesize.

       -XX:RTMAbortRatio=abort_ratio
           The RTM abort ratio is specified as a percentage (%) of all executed RTM transactions. If
           a number of aborted transactions becomes greater than this ratio, then the compiled code
           will be deoptimized. This ratio is used when the -XX:+UseRTMDeopt option is enabled. The
           default value of this option is 50. This means that the compiled code will be deoptimized
           if 50% of all transactions are aborted.

       -XX:RTMRetryCount=number_of_retries
           RTM locking code will be retried, when it is aborted or busy, the number of times
           specified by this option before falling back to the normal locking mechanism. The default
           value for this option is 5. The -XX:UseRTMLocking option must be enabled.

       -XX:-TieredCompilation
           Disables the use of tiered compilation. By default, this option is enabled. Only the Java
           HotSpot Server VM supports this option.

       -XX:+UseAES
           Enables hardware-based AES intrinsics for Intel, AMD, and SPARC hardware. Intel Westmere
           (2010 and newer), AMD Bulldozer (2011 and newer), and SPARC (T4 and newer) are the
           supported hardware. UseAES is used in conjunction with UseAESIntrinsics.

       -XX:+UseAESIntrinsics
           UseAES and UseAESIntrinsics flags are enabled by default and are supported only for Java
           HotSpot Server VM 32-bit and 64-bit. To disable hardware-based AES intrinsics, specify
           -XX:-UseAES -XX:-UseAESIntrinsics. For example, to enable hardware AES, use the following
           flags:

               -XX:+UseAES -XX:+UseAESIntrinsics

           To support UseAES and UseAESIntrinsics flags for 32-bit and 64-bit use -server option to
           choose Java HotSpot Server VM. These flags are not supported on Client VM.

       -XX:+UseCodeCacheFlushing
           Enables flushing of the code cache before shutting down the compiler. This option is
           enabled by default. To disable flushing of the code cache before shutting down the
           compiler, specify -XX:-UseCodeCacheFlushing.

       -XX:+UseCondCardMark
           Enables checking of whether the card is already marked before updating the card table.
           This option is disabled by default and should only be used on machines with multiple
           sockets, where it will increase performance of Java applications that rely heavily on
           concurrent operations. Only the Java HotSpot Server VM supports this option.

       -XX:+UseRTMDeopt
           Auto-tunes RTM locking depending on the abort ratio. This ratio is specified by
           -XX:RTMAbortRatio option. If the number of aborted transactions exceeds the abort ratio,
           then the method containing the lock will be deoptimized and recompiled with all locks as
           normal locks. This option is disabled by default. The -XX:+UseRTMLocking option must be
           enabled.

       -XX:+UseRTMLocking
           Generate Restricted Transactional Memory (RTM) locking code for all inflated locks, with
           the normal locking mechanism as the fallback handler. This option is disabled by default.
           Options related to RTM are only available for the Java HotSpot Server VM on x86 CPUs that
           support Transactional Synchronization Extensions (TSX).

           RTM is part of Intel's TSX, which is an x86 instruction set extension and facilitates the
           creation of multithreaded applications. RTM introduces the new instructions XBEGIN,
           XABORT, XEND, and XTEST. The XBEGIN and XEND instructions enclose a set of instructions
           to run as a transaction. If no conflict is found when running the transaction, the memory
           and register modifications are committed together at the XEND instruction. The XABORT
           instruction can be used to explicitly abort a transaction and the XEND instruction to
           check if a set of instructions are being run in a transaction.

           A lock on a transaction is inflated when another thread tries to access the same
           transaction, thereby blocking the thread that did not originally request access to the
           transaction. RTM requires that a fallback set of operations be specified in case a
           transaction aborts or fails. An RTM lock is a lock that has been delegated to the TSX's
           system.

           RTM improves performance for highly contended locks with low conflict in a critical
           region (which is code that must not be accessed by more than one thread concurrently).
           RTM also improves the performance of coarse-grain locking, which typically does not
           perform well in multithreaded applications. (Coarse-grain locking is the strategy of
           holding locks for long periods to minimize the overhead of taking and releasing locks,
           while fine-grained locking is the strategy of trying to achieve maximum parallelism by
           locking only when necessary and unlocking as soon as possible.) Also, for lightly
           contended locks that are used by different threads, RTM can reduce false cache line
           sharing, also known as cache line ping-pong. This occurs when multiple threads from
           different processors are accessing different resources, but the resources share the same
           cache line. As a result, the processors repeatedly invalidate the cache lines of other
           processors, which forces them to read from main memory instead of their cache.

       -XX:+UseSHA
           Enables hardware-based intrinsics for SHA crypto hash functions for SPARC hardware.
           UseSHA is used in conjunction with the UseSHA1Intrinsics, UseSHA256Intrinsics, and
           UseSHA512Intrinsics options.

           The UseSHA and UseSHA*Intrinsics flags are enabled by default, and are supported only for
           Java HotSpot Server VM 64-bit on SPARC T4 and newer.

           This feature is only applicable when using the sun.security.provider.Sun provider for SHA
           operations.

           To disable all hardware-based SHA intrinsics, specify -XX:-UseSHA. To disable only a
           particular SHA intrinsic, use the appropriate corresponding option. For example:
           -XX:-UseSHA256Intrinsics.

       -XX:+UseSHA1Intrinsics
           Enables intrinsics for SHA-1 crypto hash function.

       -XX:+UseSHA256Intrinsics
           Enables intrinsics for SHA-224 and SHA-256 crypto hash functions.

       -XX:+UseSHA512Intrinsics
           Enables intrinsics for SHA-384 and SHA-512 crypto hash functions.

       -XX:+UseSuperWord
           Enables the transformation of scalar operations into superword operations. This option is
           enabled by default. To disable the transformation of scalar operations into superword
           operations, specify -XX:-UseSuperWord. Only the Java HotSpot Server VM supports this
           option.

   Advanced Serviceability Options
       These options provide the ability to gather system information and perform extensive
       debugging.

       -XX:+ExtendedDTraceProbes
           Enables additional dtrace tool probes that impact the performance. By default, this
           option is disabled and dtrace performs only standard probes.

       -XX:+HeapDumpOnOutOfMemory
           Enables the dumping of the Java heap to a file in the current directory by using the heap
           profiler (HPROF) when a java.lang.OutOfMemoryError exception is thrown. You can
           explicitly set the heap dump file path and name using the -XX:HeapDumpPath option. By
           default, this option is disabled and the heap is not dumped when an OutOfMemoryError
           exception is thrown.

       -XX:HeapDumpPath=path
           Sets the path and file name for writing the heap dump provided by the heap profiler
           (HPROF) when the -XX:+HeapDumpOnOutOfMemoryError option is set. By default, the file is
           created in the current working directory, and it is named java_pidpid.hprof where pid is
           the identifier of the process that caused the error. The following example shows how to
           set the default file explicitly (%p represents the current process identificator):

               -XX:HeapDumpPath=./java_pid%p.hprof

           The following example shows how to set the heap dump file to
           /var/log/java/java_heapdump.hprof:

               -XX:HeapDumpPath=/var/log/java/java_heapdump.hprof


       -XX:LogFile=path
           Sets the path and file name where log data is written. By default, the file is created in
           the current working directory, and it is named hotspot.log.

           The following example shows how to set the log file to /var/log/java/hotspot.log:

               -XX:LogFile=/var/log/java/hotspot.log


       -XX:+PrintClassHistogram
           Enables printing of a class instance histogram after a Control+C event (SIGTERM). By
           default, this option is disabled.

           Setting this option is equivalent to running the jmap -histo command, or the jcmd pid
           GC.class_histogram command, where pid is the current Java process identifier.

       -XX:+PrintConcurrentLocks
           Enables printing of locks after a event. By default, this option is disabled.

           Enables printing of java.util.concurrent locks after a Control+C event (SIGTERM). By
           default, this option is disabled.

           Setting this option is equivalent to running the jstack -l command or the jcmd pid
           Thread.print -l command, where pid is the current Java process identifier.

       -XX:+UnlockDiagnosticVMOptions
           Unlocks the options intended for diagnosing the JVM. By default, this option is disabled
           and diagnostic options are not available.

   Advanced Garbage Collection Options
       These options control how garbage collection (GC) is performed by the Java HotSpot VM.

       -XX:+AggressiveHeap
           Enables Java heap optimization. This sets various parameters to be optimal for
           long-running jobs with intensive memory allocation, based on the configuration of the
           computer (RAM and CPU). By default, the option is disabled and the heap is not optimized.

       -XX:+AlwaysPreTouch
           Enables touching of every page on the Java heap during JVM initialization. This gets all
           pages into the memory before entering the main() method. The option can be used in
           testing to simulate a long-running system with all virtual memory mapped to physical
           memory. By default, this option is disabled and all pages are committed as JVM heap space
           fills.

       -XX:+CMSClassUnloadingEnabled
           Enables class unloading when using the concurrent mark-sweep (CMS) garbage collector.
           This option is enabled by default. To disable class unloading for the CMS garbage
           collector, specify -XX:-CMSClassUnloadingEnabled.

       -XX:CMSExpAvgFactor=percent
           Sets the percentage of time (0 to 100) used to weight the current sample when computing
           exponential averages for the concurrent collection statistics. By default, the
           exponential averages factor is set to 25%. The following example shows how to set the
           factor to 15%:

               -XX:CMSExpAvgFactor=15


       -XX:CMSInitiatingOccupancyFraction=percent
           Sets the percentage of the old generation occupancy (0 to 100) at which to start a CMS
           collection cycle. The default value is set to -1. Any negative value (including the
           default) implies that -XX:CMSTriggerRatio is used to define the value of the initiating
           occupancy fraction.

           The following example shows how to set the occupancy fraction to 20%:

               -XX:CMSInitiatingOccupancyFraction=20


       -XX:+CMSScavengeBeforeRemark
           Enables scavenging attempts before the CMS remark step. By default, this option is
           disabled.

       -XX:CMSTriggerRatio=percent
           Sets the percentage (0 to 100) of the value specified by -XX:MinHeapFreeRatio that is
           allocated before a CMS collection cycle commences. The default value is set to 80%.

           The following example shows how to set the occupancy fraction to 75%:

               -XX:CMSTriggerRatio=75


       -XX:ConcGCThreads=threads
           Sets the number of threads used for concurrent GC. The default value depends on the
           number of CPUs available to the JVM.

           For example, to set the number of threads for concurrent GC to 2, specify the following
           option:

               -XX:ConcGCThreads=2


       -XX:+DisableExplicitGC
           Enables the option that disables processing of calls to System.gc(). This option is
           disabled by default, meaning that calls to System.gc() are processed. If processing of
           calls to System.gc() is disabled, the JVM still performs GC when necessary.

       -XX:+ExplicitGCInvokesConcurrent
           Enables invoking of concurrent GC by using the System.gc() request. This option is
           disabled by default and can be enabled only together with the -XX:+UseConcMarkSweepGC
           option.

       -XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses
           Enables invoking of concurrent GC by using the System.gc() request and unloading of
           classes during the concurrent GC cycle. This option is disabled by default and can be
           enabled only together with the -XX:+UseConcMarkSweepGC option.

       -XX:G1HeapRegionSize=size
           Sets the size of the regions into which the Java heap is subdivided when using the
           garbage-first (G1) collector. The value can be between 1 MB and 32 MB. The default region
           size is determined ergonomically based on the heap size.

           The following example shows how to set the size of the subdivisions to 16 MB:

               -XX:G1HeapRegionSize=16m


       -XX:+G1PrintHeapRegions
           Enables the printing of information about which regions are allocated and which are
           reclaimed by the G1 collector. By default, this option is disabled.

       -XX:G1ReservePercent=percent
           Sets the percentage of the heap (0 to 50) that is reserved as a false ceiling to reduce
           the possibility of promotion failure for the G1 collector. By default, this option is set
           to 10%.

           The following example shows how to set the reserved heap to 20%:

               -XX:G1ReservePercent=20


       -XX:InitialHeapSize=size
           Sets the initial size (in bytes) of the memory allocation pool. This value must be either
           0, or a multiple of 1024 and greater than 1 MB. Append the letter k or K to indicate
           kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value
           is chosen at runtime based on system configuration. See the section "Ergonomics" in Java
           SE HotSpot Virtual Machine Garbage Collection Tuning Guide at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/index.html.

           The following examples show how to set the size of allocated memory to 6 MB using various
           units:

               -XX:InitialHeapSize=6291456
               -XX:InitialHeapSize=6144k
               -XX:InitialHeapSize=6m

           If you set this option to 0, then the initial size will be set as the sum of the sizes
           allocated for the old generation and the young generation. The size of the heap for the
           young generation can be set using the -XX:NewSize option.

       -XX:InitialSurvivorRatio=ratio
           Sets the initial survivor space ratio used by the throughput garbage collector (which is
           enabled by the -XX:+UseParallelGC and/or -XX:+UseParallelOldGC options). Adaptive sizing
           is enabled by default with the throughput garbage collector by using the
           -XX:+UseParallelGC and -XX:+UseParallelOldGC options, and survivor space is resized
           according to the application behavior, starting with the initial value. If adaptive
           sizing is disabled (using the -XX:-UseAdaptiveSizePolicy option), then the
           -XX:SurvivorRatio option should be used to set the size of the survivor space for the
           entire execution of the application.

           The following formula can be used to calculate the initial size of survivor space (S)
           based on the size of the young generation (Y), and the initial survivor space ratio (R):

               S=Y/(R+2)

           The 2 in the equation denotes two survivor spaces. The larger the value specified as the
           initial survivor space ratio, the smaller the initial survivor space size.

           By default, the initial survivor space ratio is set to 8. If the default value for the
           young generation space size is used (2 MB), the initial size of the survivor space will
           be 0.2 MB.

           The following example shows how to set the initial survivor space ratio to 4:

               -XX:InitialSurvivorRatio=4


       -XX:InitiatingHeapOccupancyPercent=percent
           Sets the percentage of the heap occupancy (0 to 100) at which to start a concurrent GC
           cycle. It is used by garbage collectors that trigger a concurrent GC cycle based on the
           occupancy of the entire heap, not just one of the generations (for example, the G1
           garbage collector).

           By default, the initiating value is set to 45%. A value of 0 implies nonstop GC cycles.
           The following example shows how to set the initiating heap occupancy to 75%:

               -XX:InitiatingHeapOccupancyPercent=75


       -XX:MaxGCPauseMillis=time
           Sets a target for the maximum GC pause time (in milliseconds). This is a soft goal, and
           the JVM will make its best effort to achieve it. By default, there is no maximum pause
           time value.

           The following example shows how to set the maximum target pause time to 500 ms:

               -XX:MaxGCPauseMillis=500


       -XX:MaxHeapSize=size
           Sets the maximum size (in byes) of the memory allocation pool. This value must be a
           multiple of 1024 and greater than 2 MB. Append the letter k or K to indicate kilobytes, m
           or M to indicate megabytes, g or G to indicate gigabytes. The default value is chosen at
           runtime based on system configuration. For server deployments, -XX:InitialHeapSize and
           -XX:MaxHeapSize are often set to the same value. See the section "Ergonomics" in Java SE
           HotSpot Virtual Machine Garbage Collection Tuning Guide at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/index.html.

           The following examples show how to set the maximum allowed size of allocated memory to 80
           MB using various units:

               -XX:MaxHeapSize=83886080
               -XX:MaxHeapSize=81920k
               -XX:MaxHeapSize=80m

           On Oracle Solaris 7 and Oracle Solaris 8 SPARC platforms, the upper limit for this value
           is approximately 4,000 MB minus overhead amounts. On Oracle Solaris 2.6 and x86
           platforms, the upper limit is approximately 2,000 MB minus overhead amounts. On Linux
           platforms, the upper limit is approximately 2,000 MB minus overhead amounts.

           The -XX:MaxHeapSize option is equivalent to -Xmx.

       -XX:MaxHeapFreeRatio=percent
           Sets the maximum allowed percentage of free heap space (0 to 100) after a GC event. If
           free heap space expands above this value, then the heap will be shrunk. By default, this
           value is set to 70%.

           The following example shows how to set the maximum free heap ratio to 75%:

               -XX:MaxHeapFreeRatio=75


       -XX:MaxMetaspaceSize=size
           Sets the maximum amount of native memory that can be allocated for class metadata. By
           default, the size is not limited. The amount of metadata for an application depends on
           the application itself, other running applications, and the amount of memory available on
           the system.

           The following example shows how to set the maximum class metadata size to 256 MB:

               -XX:MaxMetaspaceSize=256m


       -XX:MaxNewSize=size
           Sets the maximum size (in bytes) of the heap for the young generation (nursery). The
           default value is set ergonomically.

       -XX:MaxTenuringThreshold=threshold
           Sets the maximum tenuring threshold for use in adaptive GC sizing. The largest value is
           15. The default value is 15 for the parallel (throughput) collector, and 6 for the CMS
           collector.

           The following example shows how to set the maximum tenuring threshold to 10:

               -XX:MaxTenuringThreshold=10


       -XX:MetaspaceSize=size
           Sets the size of the allocated class metadata space that will trigger a garbage
           collection the first time it is exceeded. This threshold for a garbage collection is
           increased or decreased depending on the amount of metadata used. The default size depends
           on the platform.

       -XX:MinHeapFreeRatio=percent
           Sets the minimum allowed percentage of free heap space (0 to 100) after a GC event. If
           free heap space falls below this value, then the heap will be expanded. By default, this
           value is set to 40%.

           The following example shows how to set the minimum free heap ratio to 25%:

               -XX:MinHeapFreeRatio=25


       -XX:NewRatio=ratio
           Sets the ratio between young and old generation sizes. By default, this option is set to
           2. The following example shows how to set the young/old ratio to 1:

               -XX:NewRatio=1


       -XX:NewSize=size
           Sets the initial size (in bytes) of the heap for the young generation (nursery). Append
           the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate
           gigabytes.

           The young generation region of the heap is used for new objects. GC is performed in this
           region more often than in other regions. If the size for the young generation is too low,
           then a large number of minor GCs will be performed. If the size is too high, then only
           full GCs will be performed, which can take a long time to complete. Oracle recommends
           that you keep the size for the young generation between a half and a quarter of the
           overall heap size.

           The following examples show how to set the initial size of young generation to 256 MB
           using various units:

               -XX:NewSize=256m
               -XX:NewSize=262144k
               -XX:NewSize=268435456

           The -XX:NewSize option is equivalent to -Xmn.

       -XX:ParallelGCThreads=threads
           Sets the number of threads used for parallel garbage collection in the young and old
           generations. The default value depends on the number of CPUs available to the JVM.

           For example, to set the number of threads for parallel GC to 2, specify the following
           option:

               -XX:ParallelGCThreads=2


       -XX:+ParallelRefProcEnabled
           Enables parallel reference processing. By default, this option is disabled.

       -XX:+PrintAdaptiveSizePolicy
           Enables printing of information about adaptive generation sizing. By default, this option
           is disabled.

       -XX:+PrintGC
           Enables printing of messages at every GC. By default, this option is disabled.

       -XX:+PrintGCApplicationConcurrentTime
           Enables printing of how much time elapsed since the last pause (for example, a GC pause).
           By default, this option is disabled.

       -XX:+PrintGCApplicationStoppedTime
           Enables printing of how much time the pause (for example, a GC pause) lasted. By default,
           this option is disabled.

       -XX:+PrintGCDateStamps
           Enables printing of a date stamp at every GC. By default, this option is disabled.

       -XX:+PrintGCDetails
           Enables printing of detailed messages at every GC. By default, this option is disabled.

       -XX:+PrintGCTaskTimeStamps
           Enables printing of time stamps for every individual GC worker thread task. By default,
           this option is disabled.

       -XX:+PrintGCTimeStamps
           Enables printing of time stamps at every GC. By default, this option is disabled.

       -XX:+PrintStringDeduplicationStatistics
           Prints detailed deduplication statistics. By default, this option is disabled. See the
           -XX:+UseStringDeduplication option.

       -XX:+PrintTenuringDistribution
           Enables printing of tenuring age information. The following is an example of the output:

               Desired survivor size 48286924 bytes, new threshold 10 (max 10)
               - age 1: 28992024 bytes, 28992024 total
               - age 2: 1366864 bytes, 30358888 total
               - age 3: 1425912 bytes, 31784800 total
               ...

           Age 1 objects are the youngest survivors (they were created after the previous scavenge,
           survived the latest scavenge, and moved from eden to survivor space). Age 2 objects have
           survived two scavenges (during the second scavenge they were copied from one survivor
           space to the next). And so on.

           In the preceding example, 28 992 024 bytes survived one scavenge and were copied from
           eden to survivor space, 1 366 864 bytes are occupied by age 2 objects, etc. The third
           value in each row is the cumulative size of objects of age n or less.

           By default, this option is disabled.

       -XX:+ScavengeBeforeFullGC
           Enables GC of the young generation before each full GC. This option is enabled by
           default. Oracle recommends that you do not disable it, because scavenging the young
           generation before a full GC can reduce the number of objects reachable from the old
           generation space into the young generation space. To disable GC of the young generation
           before each full GC, specify -XX:-ScavengeBeforeFullGC.

       -XX:SoftRefLRUPolicyMSPerMB=time
           Sets the amount of time (in milliseconds) a softly reachable object is kept active on the
           heap after the last time it was referenced. The default value is one second of lifetime
           per free megabyte in the heap. The -XX:SoftRefLRUPolicyMSPerMB option accepts integer
           values representing milliseconds per one megabyte of the current heap size (for Java
           HotSpot Client VM) or the maximum possible heap size (for Java HotSpot Server VM). This
           difference means that the Client VM tends to flush soft references rather than grow the
           heap, whereas the Server VM tends to grow the heap rather than flush soft references. In
           the latter case, the value of the -Xmx option has a significant effect on how quickly
           soft references are garbage collected.

           The following example shows how to set the value to 2.5 seconds:

               -XX:SoftRefLRUPolicyMSPerMB=2500


       -XX:StringDeduplicationAgeThreshold=threshold
           String objects reaching the specified age are considered candidates for deduplication. An
           object's age is a measure of how many times it has survived garbage collection. This is
           sometimes referred to as tenuring; see the -XX:+PrintTenuringDistribution option. Note
           that String objects that are promoted to an old heap region before this age has been
           reached are always considered candidates for deduplication. The default value for this
           option is 3. See the -XX:+UseStringDeduplication option.

       -XX:SurvivorRatio=ratio
           Sets the ratio between eden space size and survivor space size. By default, this option
           is set to 8. The following example shows how to set the eden/survivor space ratio to 4:

               -XX:SurvivorRatio=4


       -XX:TargetSurvivorRatio=percent
           Sets the desired percentage of survivor space (0 to 100) used after young garbage
           collection. By default, this option is set to 50%.

           The following example shows how to set the target survivor space ratio to 30%:

               -XX:TargetSurvivorRatio=30


       -XX:TLABSize=size
           Sets the initial size (in bytes) of a thread-local allocation buffer (TLAB). Append the
           letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate
           gigabytes. If this option is set to 0, then the JVM chooses the initial size
           automatically.

           The following example shows how to set the initial TLAB size to 512 KB:

               -XX:TLABSize=512k


       -XX:+UseAdaptiveSizePolicy
           Enables the use of adaptive generation sizing. This option is enabled by default. To
           disable adaptive generation sizing, specify -XX:-UseAdaptiveSizePolicy and set the size
           of the memory allocation pool explicitly (see the -XX:SurvivorRatio option).

       -XX:+UseCMSInitiatingOccupancyOnly
           Enables the use of the occupancy value as the only criterion for initiating the CMS
           collector. By default, this option is disabled and other criteria may be used.

       -XX:+UseConcMarkSweepGC
           Enables the use of the CMS garbage collector for the old generation. Oracle recommends
           that you use the CMS garbage collector when application latency requirements cannot be
           met by the throughput (-XX:+UseParallelGC) garbage collector. The G1 garbage collector
           (-XX:+UseG1GC) is another alternative.

           By default, this option is disabled and the collector is chosen automatically based on
           the configuration of the machine and type of the JVM. When this option is enabled, the
           -XX:+UseParNewGC option is automatically set and you should not disable it, because the
           following combination of options has been deprecated in JDK 8: -XX:+UseConcMarkSweepGC
           -XX:-UseParNewGC.

       -XX:+UseG1GC
           Enables the use of the garbage-first (G1) garbage collector. It is a server-style garbage
           collector, targeted for multiprocessor machines with a large amount of RAM. It meets GC
           pause time goals with high probability, while maintaining good throughput. The G1
           collector is recommended for applications requiring large heaps (sizes of around 6 GB or
           larger) with limited GC latency requirements (stable and predictable pause time below 0.5
           seconds).

           By default, this option is disabled and the collector is chosen automatically based on
           the configuration of the machine and type of the JVM.

       -XX:+UseGCOverheadLimit
           Enables the use of a policy that limits the proportion of time spent by the JVM on GC
           before an OutOfMemoryError exception is thrown. This option is enabled, by default and
           the parallel GC will throw an OutOfMemoryError if more than 98% of the total time is
           spent on garbage collection and less than 2% of the heap is recovered. When the heap is
           small, this feature can be used to prevent applications from running for long periods of
           time with little or no progress. To disable this option, specify -XX:-UseGCOverheadLimit.

       -XX:+UseNUMA
           Enables performance optimization of an application on a machine with nonuniform memory
           architecture (NUMA) by increasing the application's use of lower latency memory. By
           default, this option is disabled and no optimization for NUMA is made. The option is only
           available when the parallel garbage collector is used (-XX:+UseParallelGC).

       -XX:+UseParallelGC
           Enables the use of the parallel scavenge garbage collector (also known as the throughput
           collector) to improve the performance of your application by leveraging multiple
           processors.

           By default, this option is disabled and the collector is chosen automatically based on
           the configuration of the machine and type of the JVM. If it is enabled, then the
           -XX:+UseParallelOldGC option is automatically enabled, unless you explicitly disable it.

       -XX:+UseParallelOldGC
           Enables the use of the parallel garbage collector for full GCs. By default, this option
           is disabled. Enabling it automatically enables the -XX:+UseParallelGC option.

       -XX:+UseParNewGC
           Enables the use of parallel threads for collection in the young generation. By default,
           this option is disabled. It is automatically enabled when you set the
           -XX:+UseConcMarkSweepGC option. Using the -XX:+UseParNewGC option without the
           -XX:+UseConcMarkSweepGC option was deprecated in JDK 8.

       -XX:+UseSerialGC
           Enables the use of the serial garbage collector. This is generally the best choice for
           small and simple applications that do not require any special functionality from garbage
           collection. By default, this option is disabled and the collector is chosen automatically
           based on the configuration of the machine and type of the JVM.

       -XX:+UseSHM
           On Linux, enables the JVM to use shared memory to setup large pages.

           For more information, see "Large Pages".

       -XX:+UseStringDeduplication
           Enables string deduplication. By default, this option is disabled. To use this option,
           you must enable the garbage-first (G1) garbage collector. See the -XX:+UseG1GC option.

           String deduplication reduces the memory footprint of String objects on the Java heap by
           taking advantage of the fact that many String objects are identical. Instead of each
           String object pointing to its own character array, identical String objects can point to
           and share the same character array.

       -XX:+UseTLAB
           Enables the use of thread-local allocation blocks (TLABs) in the young generation space.
           This option is enabled by default. To disable the use of TLABs, specify -XX:-UseTLAB.

   Deprecated and Removed Options
       These options were included in the previous release, but have since been considered
       unnecessary.

       -Xincgc
           Enables incremental garbage collection. This option was deprecated in JDK 8 with no
           replacement.

       -Xrunlibname
           Loads the specified debugging/profiling library. This option was superseded by the
           -agentlib option.

       -XX:CMSIncrementalDutyCycle=percent
           Sets the percentage of time (0 to 100) between minor collections that the concurrent
           collector is allowed to run. This option was deprecated in JDK 8 with no replacement,
           following the deprecation of the -XX:+CMSIncrementalMode option.

       -XX:CMSIncrementalDutyCycleMin=percent
           Sets the percentage of time (0 to 100) between minor collections that is the lower bound
           for the duty cycle when -XX:+CMSIncrementalPacing is enabled. This option was deprecated
           in JDK 8 with no replacement, following the deprecation of the -XX:+CMSIncrementalMode
           option.

       -XX:+CMSIncrementalMode
           Enables the incremental mode for the CMS collector. This option was deprecated in JDK 8
           with no replacement, along with other options that start with CMSIncremental.

       -XX:CMSIncrementalOffset=percent
           Sets the percentage of time (0 to 100) by which the incremental mode duty cycle is
           shifted to the right within the period between minor collections. This option was
           deprecated in JDK 8 with no replacement, following the deprecation of the
           -XX:+CMSIncrementalMode option.

       -XX:+CMSIncrementalPacing
           Enables automatic adjustment of the incremental mode duty cycle based on statistics
           collected while the JVM is running. This option was deprecated in JDK 8 with no
           replacement, following the deprecation of the -XX:+CMSIncrementalMode option.

       -XX:CMSIncrementalSafetyFactor=percent
           Sets the percentage of time (0 to 100) used to add conservatism when computing the duty
           cycle. This option was deprecated in JDK 8 with no replacement, following the deprecation
           of the -XX:+CMSIncrementalMode option.

       -XX:CMSInitiatingPermOccupancyFraction=percent
           Sets the percentage of the permanent generation occupancy (0 to 100) at which to start a
           GC. This option was deprecated in JDK 8 with no replacement.

       -XX:MaxPermSize=size
           Sets the maximum permanent generation space size (in bytes). This option was deprecated
           in JDK 8, and superseded by the -XX:MaxMetaspaceSize option.

       -XX:PermSize=size
           Sets the space (in bytes) allocated to the permanent generation that triggers a garbage
           collection if it is exceeded. This option was deprecated un JDK 8, and superseded by the
           -XX:MetaspaceSize option.

       -XX:+UseSplitVerifier
           Enables splitting of the verification process. By default, this option was enabled in the
           previous releases, and verification was split into two phases: type referencing
           (performed by the compiler) and type checking (performed by the JVM runtime). This option
           was deprecated in JDK 8, and verification is now split by default without a way to
           disable it.

       -XX:+UseStringCache
           Enables caching of commonly allocated strings. This option was removed from JDK 8 with no
           replacement.

PERFORMANCE TUNING EXAMPLES
       The following examples show how to use experimental tuning flags to either optimize
       throughput or to provide lower response time.

       Example 1 Tuning for Higher Throughput

               java -d64 -server -XX:+AggressiveOpts -XX:+UseLargePages -Xmn10g  -Xms26g -Xmx26g


       Example 2 Tuning for Lower Response Time

               java -d64 -XX:+UseG1GC -Xms26g Xmx26g -XX:MaxGCPauseMillis=500 -XX:+PrintGCTimeStamp


LARGE PAGES
       Also known as huge pages, large pages are memory pages that are significantly larger than the
       standard memory page size (which varies depending on the processor and operating system).
       Large pages optimize processor Translation-Lookaside Buffers.

       A Translation-Lookaside Buffer (TLB) is a page translation cache that holds the most-recently
       used virtual-to-physical address translations. TLB is a scarce system resource. A TLB miss
       can be costly as the processor must then read from the hierarchical page table, which may
       require multiple memory accesses. By using a larger memory page size, a single TLB entry can
       represent a larger memory range. There will be less pressure on TLB, and memory-intensive
       applications may have better performance.

       However, large pages page memory can negatively affect system performance. For example, when
       a large mount of memory is pinned by an application, it may create a shortage of regular
       memory and cause excessive paging in other applications and slow down the entire system.
       Also, a system that has been up for a long time could produce excessive fragmentation, which
       could make it impossible to reserve enough large page memory. When this happens, either the
       OS or JVM reverts to using regular pages.

   Large Pages Support
       Solaris and Linux support large pages.

       Solaris

           Solaris 9 and later include Multiple Page Size Support (MPSS); no additional
           configuration is necessary. See
           http://www.oracle.com/technetwork/server-storage/solaris10/overview/solaris9-features-scalability-135663.html.

       Linux

           The 2.6 kernel supports large pages. Some vendors have backported the code to their
           2.4-based releases. To check if your system can support large page memory, try the
           following:

               # cat /proc/meminfo | grep Huge
               HugePages_Total: 0
               HugePages_Free: 0
               Hugepagesize: 2048 kB


           If the output shows the three "Huge" variables, then your system can support large page
           memory but it needs to be configured. If the command prints nothing, then your system
           does not support large pages. To configure the system to use large page memory, login as
           root, and then follow these steps:

            1. If you are using the option -XX:+UseSHM (instead of -XX:+UseHugeTLBFS), then increase
               the SHMMAX value. It must be larger than the Java heap size. On a system with 4 GB of
               physical RAM (or less), the following will make all the memory sharable:

                   # echo 4294967295 > /proc/sys/kernel/shmmax


            2. If you are using the option -XX:+UseSHM or -XX:+UseHugeTLBFS, then specify the number
               of large pages. In the following example, 3 GB of a 4 GB system are reserved for
               large pages (assuming a large page size of 2048kB, then 3 GB = 3 * 1024 MB = 3072 MB
               = 3072 * 1024 kB = 3145728 kB and 3145728 kB / 2048 kB = 1536):

                   # echo 1536 > /proc/sys/vm/nr_hugepages


               Note
               ┌────────────────────────────────────────────────────┐
               │                                                    │
               │                •   Note that the values contained  │
               │                    in /proc will reset after you   │
               │                    reboot your system, so may want │
               │                    to set them in an               │
               │                    initialization script (for      │
               │                    example, rc.local or            │
               │                    sysctl.conf).                   │
               │                                                    │
               │                •   If you configure (or resize)    │
               │                    the OS kernel parameters        │
               │                    /proc/sys/kernel/shmmax or      │
               │                    /proc/sys/vm/nr_hugepages, Java │
               │                    processes may allocate large    │
               │                    pages for areas in addition to  │
               │                    the Java heap. These steps can  │
               │                    allocate large pages for the    │
               │                    following areas:                │
               │                                                    │
               │                    •   Java heap                   │
               │                                                    │
               │                    •   Code cache                  │
               │                                                    │
               │                    •   The marking bitmap data     │
               │                        structure for the parallel  │
               │                        GC                          │
               │                                                    │
               │                    Consequently, if you configure  │
               │                    the nr_hugepages parameter to   │
               │                    the size of the Java heap, then │
               │                    the JVM can fail in allocating  │
               │                    the code cache areas on large   │
               │                    pages because these areas are   │
               │                    quite large in size.            │
               └────────────────────────────────────────────────────┘


EXIT STATUS
       The following exit values are typically returned by the launcher when the launcher is called
       with the wrong arguments, serious errors, or exceptions thrown by the JVM. However, a Java
       application may choose to return any value by using the API call System.exit(exitValue). The
       values are:

       •   0: Successful completion

       •   >0: An error occurred

SEE ALSO
       •   javac(1)

       •   jdb(1)

       •   javah(1)

       •   jar(1)

       •   jstat(1)

JDK 8                                       03 March 2015                                    java(1)