_JAVA_OPTIONS, JAVA_TOOL_OPTIONS, and JAVA_OPTS: What's the Difference and When Should You Use Them?

Exploring the Differences between _JAVA_OPTIONS, JAVA_TOOL_OPTIONS, and JAVA_OPTS

As you've astutely observed, _JAVA_OPTIONS, JAVA_TOOL_OPTIONS, and JAVA_OPTS are all mechanisms for specifying JVM arguments. Let's delve into their similarities and distinctions.

Official Documentation

_JAVA_OPTIONS lacks official documentation, while JAVA_TOOL_OPTIONS is briefly mentioned as a way to provide VM arguments in scenarios where command-line access is limited.

Precedence

The precedence of these variables is as follows:

1. _JAVA_OPTIONS (overwrites others)
2. Command-line parameters
3. JAVA_TOOL_OPTIONS (is overwritten by others)

Functionality

_JAVA_OPTIONS and JAVA_TOOL_OPTIONS both allow you to pass JVM arguments via environment variables. However, _JAVA_OPTIONS trumps command-line arguments, which in turn trump JAVA_TOOL_OPTIONS.

Applicability

Both _JAVA_OPTIONS and JAVA_TOOL_OPTIONS are known to be picked up by java and javac. In-process JVM invocations through library calls also respect these variables.

Limitations

There are no known limitations on what can be included in _JAVA_OPTIONS or JAVA_TOOL_OPTIONS. However, setting them in ~/.bashrc is considered an abuse of their intended purpose.

Support in JVMs

_JAVA_OPTIONS is not part of the JDK, but other applications may utilize it. JAVA_TOOL_OPTIONS and JAVA_OPTS are part of the JVM. It's important to note that support for _JAVA_OPTIONS may not be guaranteed in non-Oracle HotSpot JVMs.

Recommendation

While _JAVA_OPTIONS may seem appealing due to its precedence, it's not recommended for use since it lacks documentation. JAVA_TOOL_OPTIONS serves a specific purpose and should be used only when command-line access is not feasible. JAVA_OPTS, while not directly related to the JVM, is a common placeholder for JVM arguments in scripts and batch files.

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