Additional environment variables and command-line options

Most environment variables and command-line options come from the Eclipse OpenJ9 VM, but the SDK adds a few more.

Environment variables

The environment variables that are recognized by the OpenJ9 VM are described in Environment variables. The following additional environment variables are recognized while using the SDK:
IBM_JVM_DEBUG_PROG=<debugger> (Linux® only)
Set this variable to start the VM under the specified debugger.
IBM_MALLOCTRACE=TRUE
Setting this variable to a non-null value lets you trace memory allocation in the VM. You can use this variable with the -Dcom.ibm.dbgmalloc=true system property to trace native allocations from the Java™ classes. This variable is equivalent to the command-line option -Xcheck:memory.
IBM_USE_FLOATING_STACKS=TRUE (Linux only)
Set this variable to override the automatic disabling of floating stacks. If this variable is not set, the launcher might set LD_ASSUME_KERNEL=2.2.5.
IBM_JAVA_COMMAND_LINE
The IBM_JAVA_COMMAND_LINE environment variable is set by the JVM after it starts. Using this variable, you can find the command-line parameters that are set when the JVM started. This setting is not available if the JVM is launched by using JNI. An equivalent of this variable that is called OPENJ9_JAVA_COMMAND_LINE is available in OpenJ9. The OpenJ9 setting is available when the applications are launched either from Java or JNI. Unless you are launching your application using JNI, you can continue to use IBM_JAVA_COMMAND_LINE as before.

Command-line options

The command-line options that are recognized by the OpenJ9 VM are described in OpenJ9 command-line options. The following additional command-line options are recognized when using the SDK:

-Xifa:<on | off | force> (z/OS® only)

z/OS can run Java applications on a type of special-purpose assist processor that is called the System z® Integrated Information Processor (zIIP). The zIIP supersedes the System z Application Assist Processor (zAAP), which was previously known as an IFA (Integrated Facility for Applications).

The -Xifa option enables Java applications to run on zIIPs if they are available. The default value for the -Xifa option is on.

Note: The force option is obsolete and should not be used. This option is superseded by the SYS1.PARMLIB(IEAOPTxx) PROJECTCPU=YES parameter, which is available on all supported levels of z/OS. Xifa:force can be used for testing purposes when a zIIP is not available, but can have a negative performance impact.