I thought it would be great to have a comparison between _JAVA_OPTIONS and JAVA_TOOL_OPTIONS.
I have been searching a bit for one, but I cannot find anything, so I hope we can find the knowledge here on Stackoverflow.

JAVA_OPTS is included for completeness. It is not part of the JVM, but there is a lot of questions about it out in the wild.

What I know:

So far I have found out that:

• JAVA_OPTS is not used by the JDK, but by a bunch of other apps (see this post).
• JAVA_TOOL_OPTIONS and _JAVA_OPTIONS are ways to specify JVM arguments as an environment variable instead of command line parameters.
  • The are picked up by at least java and javac
  • They have this precedence:
    1. _JAVA_OPTIONS (overwrites the others)
    2. Command line parameters
    3. JAVA_TOOL_OPTIONS (is overwritten by the others)

What I would like to know

• Are there any official documentation comparing JAVA_TOOL_OPTIONS and _JAVA_OPTIONS
• Are there any other differences between JAVA_TOOL_OPTIONS and _JAVA_OPTIONS (except from precedence).
• Which executables pick up JAVA_TOOL_OPTIONS and _JAVA_OPTIONS (in addition to java and javac)
• Any limitation on what can be included on JAVA_TOOL_OPTIONS and _JAVA_OPTIONS

Official Documentation

I have not been able to find any documentation about _JAVA_OPTIONS. The documentation for JAVA_TOOL_OPTIONS does not shed much light on the difference:

Since the command-line cannot always be accessed or modified, for example in embedded VMs or simply VMs launched deep within scripts, a JAVA_TOOL_OPTIONS variable is provided so that agents may be launched in these cases.
…

Example script

This is the code I used to figure this out. Console output is included as comments:

export JAVA_OPTS=foobar
export JAVA_TOOL_OPTIONS= 
export _JAVA_OPTIONS="-Xmx512m -Xms64m"

java -version                          
# Picked up JAVA_TOOL_OPTIONS: 
# Picked up _JAVA_OPTIONS: -Xmx512m -Xms64m
# java version "1.7.0_40"
OpenJDK Runtime Environment (IcedTea 2.4.1) (suse-3.41.1-x86_64)
OpenJDK 64-Bit Server VM (build 24.0-b50, mixed mode)

javac -version
# Picked up JAVA_TOOL_OPTIONS: 
# Picked up _JAVA_OPTIONS: -Xmx512m -Xms64m
# javac 1.7.0_40

export JAVA_TOOL_OPTIONS="-Xmx1 -Xms1"
export _JAVA_OPTIONS="-Xmx512m -Xms64m"
javac -version
# Picked up JAVA_TOOL_OPTIONS: -Xmx1 -Xms1
# Picked up _JAVA_OPTIONS: -Xmx512m -Xms64m
# javac 1.7.0_40

export JAVA_TOOL_OPTIONS="-Xmx512m -Xms64m"
export _JAVA_OPTIONS="-Xmx1 -Xms1"
javac -version
# Picked up JAVA_TOOL_OPTIONS: -Xmx512m -Xms64m
# Picked up _JAVA_OPTIONS: -Xmx1 -Xms1
# Error occurred during initialization of VM
# Too small initial heap

export JAVA_TOOL_OPTIONS="-Xmx1 -Xms1"
export _JAVA_OPTIONS=
java -Xmx512m -Xms64m -version
# Picked up JAVA_TOOL_OPTIONS: -Xmx1 -Xms1
# Picked up _JAVA_OPTIONS: 
# java version "1.7.0_40"
# OpenJDK Runtime Environment (IcedTea 2.4.1) (suse-3.41.1-x86_64)
# OpenJDK 64-Bit Server VM (build 24.0-b50, mixed mode)

export JAVA_TOOL_OPTIONS=
export _JAVA_OPTIONS="-Xmx1 -Xms1"
java -Xmx512m -Xms64m -version
# Picked up JAVA_TOOL_OPTIONS: 
# Picked up _JAVA_OPTIONS: -Xmx1 -Xms1
# Error occurred during initialization of VM
# Too small initial heap