Openjdk-11-jre Not Headless

6 min read Oct 03, 2024

Why Is My OpenJDK 11 JRE Not Headless?

You're trying to run a Java application that requires a headless environment, but you're encountering the error "openjdk-11-jre not headless". This means your OpenJDK 11 JRE is configured to run with a graphical user interface (GUI) instead of a command-line interface, which is necessary for headless operations. This is a common problem faced by developers, especially when working with server-side applications or automation scripts.

Let's delve into the reasons behind this error and explore solutions to ensure your OpenJDK 11 JRE runs in a headless environment.

Understanding Headless Mode

The term "headless" refers to a Java runtime environment (JRE) that operates without a graphical user interface (GUI). It is ideal for server-side applications, command-line tools, and automated tasks that don't require visual elements. Headless mode is essential when you want to run Java programs remotely, without a physical display connected to your machine.

Why is My OpenJDK 11 JRE Not Headless?

There are several reasons why you might encounter the "openjdk-11-jre not headless" error:

Incorrect Environment Variables: The DISPLAY environment variable might be set, which indicates a graphical environment is available, even though you're trying to run in headless mode.
GUI-Based JavaFX Libraries: If your application relies on JavaFX libraries, which require a GUI environment, you'll need to make sure JavaFX is properly configured for headless operation.
Missing Dependencies: The necessary libraries and packages for headless operation might be missing from your system.
Conflicting Configurations: Multiple JRE versions or configurations might be conflicting, causing your application to default to a non-headless setup.

Troubleshooting and Solutions

Here's a step-by-step guide to troubleshoot and fix the "openjdk-11-jre not headless" error:

Verify Environment Variables:
- Linux/macOS: Use the command echo $DISPLAY to check if the DISPLAY environment variable is set. If it is, you can unset it by running unset DISPLAY.
- Windows: In the command prompt, use set DISPLAY to see if the variable is set. If it is, you can unset it by running set DISPLAY=.
Configure JavaFX for Headless Mode:
- If your application uses JavaFX libraries, ensure they are configured for headless operation. You can achieve this by adding the following Java property to your command line:
```
java -Djava.awt.headless=true ...
```
Install Necessary Dependencies:
- On some systems, additional packages might be required for headless operation. For example, on Debian-based distributions, you can install the libxtst6 and libxrender1 packages.
Check for Conflicting Configurations:
- If you have multiple Java installations, ensure that the one you're using for headless operation is properly configured and has the necessary libraries.
- You can use the command java -version to check the current Java version and make sure it matches the version you intend to use.

Examples:

Here are some examples of how to use the -Djava.awt.headless=true property in your Java application:

Running a Java application from the command line:

java -Djava.awt.headless=true -jar myapplication.jar

Setting the headless property in your Java code:

public static void main(String[] args) {
   System.setProperty("java.awt.headless", "true");
   // Rest of your application logic
}

Conclusion

By understanding the causes of the "openjdk-11-jre not headless" error and following the troubleshooting steps outlined above, you can successfully run your Java applications in a headless environment. This allows you to leverage the power of Java for server-side tasks and automation without relying on a graphical interface.