_JAVA_OPTIONS Environment Variable in Java

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Mohd Mohtashim Nawaz Oct 18, 2023
Java Java Options
  1. Types of Java Options
  2. _JAVA_OPTIONS Environment Variable in Java
  3. Setting _JAVA_OPTIONS
  4. Common Use Cases of _JAVA_OPTIONS
  5. Caveats and Best Practices
  6. JAVA_TOOL_OPTIONS Environment Variable in Java
  7. Difference Between JAVA_TOOL_OPTIONS and _JAVA_OPTIONS
  8. Conclusion
_JAVA_OPTIONS Environment Variable in Java

The _JAVA_OPTIONS is an environment variable that you can use to pass the Java options to a JVM process. The passed Java options are treated similarly to the command line arguments by the Java Virtual Machine.

In this article, we will understand different types of Java options. It also introduces two pivotal environment variables, _JAVA_OPTIONS and JAVA_TOOL_OPTIONS, crucial for customizing JVM behavior and fine-tuning JDK tools, respectively.

Additionally, we’ll discern the difference between JAVA_TOOL_OPTIONS and _JAVA_OPTIONS, guiding developers toward making informed choices in their Java development endeavors.

Types of Java Options

Java defines three different types of options. Java differentiates between options based on their support in different Java versions and their usage.

Let us understand each of these options categories.

  1. Standard Options - Java guarantees that all Java versions support standard options. Java enables the use of these options for common actions such as:
    • Setting the classpath variable.
    • Checking the version of Java Runtime Environment (JRE).
    • Toggling the verbose output, etc.
  2. Extra Options - Java does not guarantee the support of these types of options in all versions. These options are specifically related to Java HotSpot Virtual Machine and can change. Java uses these options to set specific variables.
  3. Advanced Options - Java provides advanced options for developers. Developers can use these options to tune JVM, JRE, JIT, and Garbage Collector.

There are four different types of advanced options. These are given as follows:

  1. Runtime Options - Developers can use these options to tune the run time of JVM.
  2. JIT Compiler Options - Developers can use these options to control the Just In Time (JIT) Java compiler.
  3. Serviceability Options - Java defines these options for debugging and gathering system information.
  4. Garbage Collection Options - Developers can control the garbage collection mechanism of Java using these options.

_JAVA_OPTIONS Environment Variable in Java

Java defines several environment variables to pass the Java options to the JVM during the execution of a process. The _JAVA_OPTIONS is one such environment variable.

_JAVA_OPTIONS is an environment variable used to pass arguments and parameters to the Java Virtual Machine (JVM) when it starts. It allows developers and administrators to customize the behavior of the JVM according to their specific requirements.

This environment variable is particularly useful in scenarios where you want to adjust JVM memory settings, enable or disable specific JVM features or options, debug or profile Java applications, and set system properties that affect the application’s behavior.

Java treats the arguments you pass using this environment variable similar to the command line arguments. In fact, as per the documentation of Java by Oracle, Java provides these options so that command-line arguments can be passed to programs in those execution environments where a direct command line is not available.

You can pass multiple arguments where each argument is separated by white space. If your argument contains white space, you should enclose it within quotes.

You should be careful while using the _JAVA_OPTIONS because the program’s execution will fail if the arguments are invalid.

Setting _JAVA_OPTIONS

Setting _JAVA_OPTIONS is relatively straightforward. It involves defining the variable with the desired values before launching a Java application.

This can be done via the command line or by configuring it in your system’s environment variables.

Command Line:

export _JAVA_OPTIONS=<options>
java <your_program>

Environment Variables:

  1. Windows:
    • Open the Control Panel.
    • Navigate to System and Security > System > Advanced system settings.
    • Click on the "Environment Variables" button.
    • Under "System variables", click "New...", and add _JAVA_OPTIONS with the desired value.
  2. Linux/Unix:

    • Open the terminal.

    • Edit your shell profile file (e.g., ~/.bashrc for Bash, ~/.zshrc for Zsh) and add the following line:

      export _JAVA_OPTIONS=<options>
  3. macOS:

    • Open the terminal.

    • Edit your shell profile file (usually ~/.bash_profile or ~/.zshrc) and add:

      export _JAVA_OPTIONS=<options>

Common Use Cases of _JAVA_OPTIONS

Memory Configuration

One of the most common uses of _JAVA_OPTIONS is to allocate memory to the JVM. This is crucial for performance optimization, especially for memory-intensive applications.

export _JAVA_OPTIONS="-Xmx512m -Xms256m"

In this example, we’ve set the maximum heap size (-Xmx) to 512MB and the initial heap size (-Xms) to 256MB.

Enabling Garbage Collection Logs

For diagnosing memory-related issues, enabling garbage collection logs can provide valuable insights.

export _JAVA_OPTIONS="-Xlog:gc*:file=/path/to/gc.log:time,uptime:filecount=5,filesize=10M"

This command configures the JVM to log garbage collection information to a file specified by file=/path/to/gc.log. It rotates logs when they reach 10MB and keeps up to 5 files.

Debugging and Profiling

Enabling remote debugging or profiling can be essential for troubleshooting and optimizing Java applications.

export _JAVA_OPTIONS="-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005"

This command enables the Java Debug Wire Protocol (JDWP) on port 5005.

Caveats and Best Practices

  1. Be Mindful of Overriding: Be cautious when using _JAVA_OPTIONS as it can override other JVM settings.
  2. Quoting Values: If your options contain spaces or special characters, it’s essential to enclose them in double quotes (").
  3. Separating Multiple Options: If you need to specify multiple options, separate them with spaces.
  4. Keep It Specific: Avoid setting global options that could potentially affect unrelated Java applications.
  5. Logging and Monitoring: Use the logs and monitoring tools to evaluate the effects of your configurations on application performance.
  6. Documentation: Always document the _JAVA_OPTIONS you set to make it easier for others to understand and maintain the system.

JAVA_TOOL_OPTIONS Environment Variable in Java

The JAVA_TOOL_OPTIONS is the successor of the _JAVA_OPTIONS. The _JAVA_OPTIONS environment variable is not standardized in the JVM specification. Therefore, different vendors have their names for this variable.

However, the JAVA_TOOL_OPTIONS variable is standardized in the JVM specification. You should always prefer it over the _JAVA_OPTIONS. This is because it handles the white space issues and quotations better.

JAVA_TOOL_OPTIONS is another environment variable used to pass options and parameters to the Java Virtual Machine (JVM) when it starts. Similar to _JAVA_OPTIONS, it allows for customization of the JVM’s behavior to suit specific requirements.

However, there is a key distinction between JAVA_TOOL_OPTIONS and _JAVA_OPTIONS. While _JAVA_OPTIONS is recognized by all Java applications, JAVA_TOOL_OPTIONS is specifically intended for tools and utilities that are part of the Java Development Kit (JDK), such as javac, java, javadoc, and others.

This means that if you set JAVA_TOOL_OPTIONS, the options specified will only apply when running these JDK tools. This can be extremely useful for scenarios where you need to customize the behavior of a specific tool without affecting the behavior of other Java applications.

Setting JAVA_TOOL_OPTIONS is done similarly to _JAVA_OPTIONS. You can either define it via the command line or by configuring it in your system’s environment variables.

Difference Between JAVA_TOOL_OPTIONS and _JAVA_OPTIONS

JAVA_TOOL_OPTIONS and _JAVA_OPTIONS are both environment variables used to pass options and parameters to the Java Virtual Machine (JVM) when it starts. However, they serve different purposes and have distinct scopes of influence:

  1. Scope of Influence:
    • JAVA_TOOL_OPTIONS: This environment variable is specifically intended for customizing the behavior of tools and utilities that are part of the Java Development Kit (JDK), such as javac, java, javadoc, and others. Options set in JAVA_TOOL_OPTIONS only apply when running these JDK tools.
    • _JAVA_OPTIONS: This environment variable affects all Java applications, not just JDK tools. It applies globally to any Java program that is executed, including user-written applications and third-party software.
  2. Specific Use Cases:
    • JAVA_TOOL_OPTIONS: It is primarily used for customizing the behavior of JDK tools. This can be especially useful when you want to configure a specific tool without affecting the behavior of other Java applications.
    • _JAVA_OPTIONS: It is used for a wider range of purposes, including setting memory options, enabling garbage collection logs, debugging, profiling, and more. It is a versatile variable for customizing the JVM’s behavior for various applications.
  3. Examples of Usage:
    • JAVA_TOOL_OPTIONS:
      • Setting compiler options for javac.
      • Configuring specific behavior for javadoc.
    • _JAVA_OPTIONS:
      • Adjusting memory settings (e.g., -Xmx, -Xms).
      • Enabling garbage collection logs (e.g., -Xlog:gc*).
      • Enabling remote debugging (e.g., -agentlib:jdwp).
  4. Recommendations:
    • JAVA_TOOL_OPTIONS: Use this when you need to customize the behavior of specific JDK tools without affecting other Java applications.
    • _JAVA_OPTIONS: Use this when you want to set JVM options globally for all Java applications. Be cautious, as this can potentially override other JVM settings.

In summary, JAVA_TOOL_OPTIONS is tailored for customizing the behavior of JDK tools, whereas _JAVA_OPTIONS is a more versatile environment variable that applies to all Java applications. The choice between them depends on the specific requirements of your development or operational environment.

Conclusion

This guide provided a detailed overview of Java options, categorizing them into standard, extra, and advanced types.

We highlighted the significance of _JAVA_OPTIONS in customizing JVM behavior, covering memory allocation, garbage collection logs, and debugging. Additionally, we introduced JAVA_TOOL_OPTIONS as a standardized alternative for fine-tuning JDK tools.

Understanding and utilizing these environment variables are essential for optimizing Java applications to meet specific requirements. Remember to apply them judiciously in your development endeavors.