Other nonstandard options

These -X options are nonstandard and subject to change without notice.

For options that take <size> parameter, you should suffix the number with "k" or "K" to indicate kilobytes, "m" or "M" to indicate megabytes, or "g" or "G" to indicate gigabytes.
-Xaot[:<suboption>,suboption,...]
Enables the AOT compiler if -Xshareclasses is also present. For details of the suboptions, see the Diagnostics Guide. See also -Xnoaot. By default, the AOT compiler is enabled, but it is only active in conjunction with -Xshareclasses.
-Xargencoding
Allows you to put Unicode escape sequences in the argument list. This option is set to off by default.
-Xbootclasspath:<directories and .zip or .jar files separated by : >
Sets the search path for bootstrap classes and resources. The default is to search for bootstrap classes and resources in the internal VM directories and .jar files.
-Xbootclasspath/a:<directories and .zip or .jar files separated by : >
Appends the specified directories, .zip, or .jar files to the end of bootstrap class path. The default is to search for bootstrap classes and resources in the internal VM directories and .jar files.
-Xbootclasspath/p:<directories and .zip or .jar files separated by : >
Prepends the specified directories, .zip, or .jar files to the front of the bootstrap class path. Do not deploy applications that use the -Xbootclasspath: or -Xbootclasspath/p: option to override a class in the standard API, because such a deployment contravenes the Java™ 2 Runtime Environment binary code license. The default is to search for bootstrap classes and resources in the internal VM directories and .jar files.
-Xcheck:jni
Performs additional checks for JNI functions. You can also use -Xrunjnichk. By default, no checking is performed.
-Xcheck:nabounds
Performs additional checks for JNI array operations. You can also use -Xrunjnichk. By default, no checking is performed.
-Xcodecache<size>
Sets the unit size of which memory blocks are allocated to store native code of compiled Java methods. An appropriate size can be chosen for the application being run. By default, this is selected internally according to the CPU architecture and the capability of your system.
Start of change-XcompressedrefsEnd of change
Start of changeUses 32-bit values for references.End of change
Start of change-XnocompressedrefsEnd of change
Start of changeUses 64-bit values for references. From WebSphere® Real Time for AIX® on 64-bit POWER® V2 SR3, the 64-bit JVM uses compressed references. If you use this option the JVM will not start.End of change
-Xdbg:<options>
Loads debugging libraries to support the remote debugging of applications. Specifying -Xrunjdwp provides the same support. By default, the debugging libraries are not loaded, and the VM instance is not enabled for debug.
-Xdbginfo:<path to symbol file>
Loads and passes options to the debug information server. By default, the debug information server is disabled.
-Xdisablejavadump
Turns off javadump generation on errors and signals. By default, javadump generation is enabled.
-Xfuture
Turns on strict class-file format checks. Use this flag when you are developing new code because stricter checks will become the default in future releases. By default, strict format checks are disabled.
-Xint
Makes the JVM use only the Interpreter, disabling the Just-In-Time (JIT) compiler. By default, the JIT compiler is enabled.
-Xiss<size>
Sets the initial Java thread stack size. 2 KB by default.
-Xjit[:<suboption>,suboption,...]
Enables the JIT. For details of the suboptions, see theDiagnostics Guide. See also -Xnojit. By default, the JIT is enabled.
-Xlinenumbers
Displays line numbers in stack traces, for debugging. See also -Xnolinenumbers. By default, line numbers are on.
-Xlp<size>
Requests the JVM to allocate the Java heap (the heap from which Java objects are allocated) with 16 MB large pages, if a size is not specified. If large pages are not available, the Java heap is allocated with AIX's standard 4 KB pages. AIX requires special configuration to enable large pages. For more information on configuring AIX support for large pages, see http://www.ibm.com/servers/aix/whitepapers/large_page.html. The SDK uses shmget() with the SHM_LGPG and SHM_PIN flags to allocate large pages. By default, large pages are not used.
The options available for <size> are:
  • -Xlp4K
  • -Xlp64K (AIX v5.3 and later)
  • -Xlp16M (AIX v5.2 and later)
  • -Xlp16G (AIX v5.3 and later)
-Xmca<size>
Sets the expansion step for the memory allocated to store the RAM portion of loaded classes. Each time more memory is required to store classes in RAM, the allocated memory is increased by this amount. By default, the expansion step is 32 KB.
-Xmco<size>
Sets the expansion step for the memory allocated to store the ROM portion of loaded classes. Each time more memory is required to store classes in ROM, the allocated memory is increased by this amount. By default, the expansion step is 128 KB.
-Xmso<size>
Sets the C stack size for forked Java threads. By default, this option is set to 32 KB on 32-bit platforms and 256 KB on 64-bit platforms.
-Xmx<size>
Sets maximum Java heap size.The default is 64 MB.
-Xnoaot
Disables the AOT (Ahead-of-time) compiler. See also -Xaot. By default, the AOT compiler is enabled, but it is only active in conjunction with -Xshareclasses.
-Xnojit
Disables the JIT compiler. See also -Xjit. By default, the JIT compiler is enabled.
-Xnolinenumbers
Disables the line numbers for debugging. See also -Xlinenumbers. By default, line number are on.
-Xnosigcatch
Disables JVM signal handling code. See also -Xsigcatch. By default, signal handling is enabled.
-Xnosigchain
Disables signal handler chaining. See also -Xsigchain. By default, the signal handler chaining is enabled.
-Xoptionsfile=<file>
Specifies a file that contains JVM options and defines. By default, no option file is used.
-Xoss<size>
Sets the Java stack size and C stack size for any thread. This option is provided for compatibility and is equivalent to setting both -Xss and -Xmso to the specified value.The default is 400® KB.
-Xquickstart
Improves startup time by delaying JIT compilation and optimizations. By default, quickstart is disabled and there is no delay in JIT compilation.
-Xrdbginfo:<host>:<port>
Loads and passes options to the remote debug information server. By default, the remote debug information server is disabled.
-Xrealtime
Runs the JVM in a real-time mode. In particular, it will run with -Xgcpolicy:metronome
-Xrs
Disables signal handling in the JVM. Setting -Xrs prevents the Java runtime from handling any internally or externally generated signals such as SIGSEGV and SIGABRT. Any signals raised are handled by the default operating system handlers. For more information on how the VM makes full use of operating system signals, see the Diagnostics Guide.
-Xrun<library name>[:options]
Loads helper libraries. To load multiple libraries, specify it more than once on the command line. Examples of these libraries are:
-Xrunhprof[:help] | [:<option>=<value>, ...]
Performs heap, CPU, or monitor profiling. For more information, see the Diagnostics Guide.
-Xrunjdwp[:help] | [:<option>=<value>, ...]
Loads debugging libraries to support the remote debugging of applications. This is the same as -Xdbg. For more information, see the Diagnostics Guide.
-Xrunjnichk[:help] | [:<option>=<value>, ...]
Performs additional checks for JNI functions, to trace errors in native programs that access the JVM using JNI. For more information, see the Diagnostics Guide.
-Xscmx<size>[k|m|g]
For details of -Xscmx, see Class data sharing command-line options.
-Xsigcatch
Enables VM signal handling code. See also -Xnosigcatch. By default, signal handling is enabled
-Xsigchain
Enables signal handler chaining. See also -Xnosigchain. By default, signal handler chaining is enabled.
-Xsoftrefthreshold<number>
Sets the number of GCs after which a soft reference will be cleared if its referent has not been marked. The default is 3, meaning that on the third GC where the referent is not marked the soft reference will be cleared.
-Xss<size>
Sets the maximum Java stack size for any thread. The default is 1024 KB.
-Xthr:<options>
Sets the threading options.
-Xverify
Enables strict class checking for every class that is loaded. By default, strict class checking is disabled.
-Xverify:none
Disables strict class checking. By default, strict class checking is disabled.


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