Deciphering Differences between _JAVA_OPTIONS, JAVA_TOOL_OPTIONS, and JAVA_OPTS

In the realm of Java Virtual Machine (JVM) configuration, three environment variables serve distinct purposes: _JAVA_OPTIONS, JAVA_TOOL_OPTIONS, and JAVA_OPTS. While JAVA_OPTS is external to the JVM, the other two provide an alternative to command-line parameters for specifying JVM arguments.

_JAVA_OPTIONS vs. JAVA_TOOL_OPTIONS

Both _JAVA_OPTIONS and JAVA_TOOL_OPTIONS allow for setting JVM arguments via environment variables. However, they differ in their precedence and scope. _JAVA_OPTIONS holds the highest precedence, overwriting any settings specified in JAVA_TOOL_OPTIONS or command-line parameters. In contrast, JAVA_TOOL_OPTIONS has the lowest precedence, being overridden by both _JAVA_OPTIONS and command-line arguments.

Applicability

JAVA_TOOL_OPTIONS and _JAVA_OPTIONS are utilized by several executables within the Java ecosystem. In addition to Java and javac, they are also picked up by Javadoc, jar, and the Java Native Interface (JNI).

Limitations

While there are no explicit restrictions on the arguments that can be included in JAVA_TOOL_OPTIONS and _JAVA_OPTIONS, incorrect or conflicting settings can lead to unexpected behavior. It is advisable to prioritize the use of command-line parameters, reserving these environment variables for scenarios where modifying the command line is impractical or impossible.

Caveats

It is important to note that _JAVA_OPTIONS is undocumented and its use is not recommended. There is no guarantee that future JVM implementations will support this variable. Additionally, remember that the precedence order is _JAVA_OPTIONS > command-line arguments > JAVA_TOOL_OPTIONS.