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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:
o Standard Options
o Non-Standard Options
o Advanced Runtime Options
o Advanced JIT Compiler Options
o Advanced Serviceability Options
o 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:
o The java.lang.instrument package description at
http://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html
o 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:
o jar(1)
o The Java Archive (JAR) Files guide at
http://docs.oracle.com/javase/8/docs/technotes/guides/jar/index.html
o 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:
o SIGQUIT thread dumps are not available.
o 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:
o Linux/ARM (32-bit): 320 KB
o Linux/i386 (32-bit): 320 KB
o Linux/x64 (64-bit): 1024 KB
o OS X (64-bit): 1024 KB
o Oracle Solaris/i386 (32-bit): 320 KB
o 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:
o The java.ext.dirs or java.endorsed.dirs system property is set.
o The lib/endorsed directory exists and is not empty.
o The lib/ext directory contains any JAR files other than those of the JDK.
o 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:
o Linux/ARM (32-bit): 320 KB
o Linux/i386 (32-bit): 320 KB
o Linux/x64 (64-bit): 1024 KB
o OS X (64-bit): 1024 KB
o Oracle Solaris/i386 (32-bit): 320 KB
o 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
+-------------------------------------------------+
| |
| o 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). |
| |
| o 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: |
| |
| o Java heap |
| |
| o Code cache |
| |
| o 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:
o 0: Successful completion
o >0: An error occurred
SEE ALSO
o javac(1)
o jdb(1)
o javah(1)
o jar(1)
o jstat(1)
JDK 8 03 March 2015 java(1)
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