How to Check Java Version Installed on Linux

Java is a versatile and widely used programming language, and having the right Java version on your Linux system is crucial for both developers and general users. But how can you check which Java version is currently installed on your Linux machine? In this comprehensive guide, we will explore various methods to help you accurately identify the installed Java version on your Linux system, regardless of your expertise level.

Java is a fundamental component for many applications and services on Linux. Whether you’re a developer working on Java-based projects or a casual user, knowing your Java version is essential for maintaining compatibility and security. This guide will provide you with step-by-step instructions, troubleshooting tips, and additional resources to make this task a breeze.

Identifying the Java Installation

Checking for the “java” Command

The simplest way to check for your Java version is by using the “java” command. Follow these steps:

1. Open a terminal by pressing Ctrl + Alt + T or searching for “Terminal” in your application menu.
2. Execute the following command:

java -version

3. The output will display detailed information about the installed Java version, including the version number. Look for a line that starts with “openjdk” or “java version.”

Using the “update-alternatives” Command

On Debian-based Linux distributions like Ubuntu, you can use the “update-alternatives” command for a more organized way of listing installed Java versions and selecting the desired one.

1. Open a terminal.
2. List available Java installations:

sudo update-alternatives --list java

3. Select the Java version you want:

sudo update-alternatives --config java

This command will prompt you to choose from the available Java versions on your system.

Verifying the “javac” Command for JDK

If you’re specifically looking for the Java Development Kit (JDK) version, you can use the “javac” command.

1. Open a terminal.
2. Execute the following command to check the JDK version:

javac -version

3. The output will provide detailed information about your Java installation, including the Java version. Look for a line that starts with “openjdk” or “java version.”

Understanding the version format is essential to interpret the output correctly. It typically follows this pattern:

• java version "1.8.0_302"
• OpenJDK Runtime Environment (build 1.8.0_302-b08)
• OpenJDK 64-Bit Server VM (build 25.302-b08, mixed mode)

In the example above, the Java version is “1.8.0_302.”

Checking Java Version via “java -showversion”

The “java -showversion” command provides an extended version of information, which can be useful for specific purposes. Here’s how it differs from “java -version“:

1. Open a terminal.
2. Enter the following command:

java -showversion

3. The output will contain detailed information about your Java installation, including additional build and platform details.

This extended information can be beneficial in diagnosing certain issues or when detailed version information is required for compatibility checks.

Checking Java Version in GUI (Graphical User Interface)

For those who prefer graphical tools, several Linux distributions offer built-in options to check the Java version.

Utilizing GUI Tools for Beginners

For users who are less comfortable with the command line, graphical tools can provide a more user-friendly way to check the Java version. These tools are typically found in the “System Settings” or “Control Center” of your Linux distribution.

Popular Linux Distributions with Graphical Tools

1. Ubuntu

• On Ubuntu, you can use the “Software & Updates” application to manage your software sources and check Java versions.

2. Fedora

• On Fedora, you can use the “Software” application to manage your software installations and updates.

3. OpenSUSE

• OpenSUSE provides the YaST (Yet another Setup Tool) for system configuration. You can check Java versions within the YaST interface.

4. CentOS

• CentOS offers a graphical package manager that can display installed Java versions.

Navigating to the Java Information

Regardless of your Linux distribution, the steps to access the Java version information through a graphical tool are generally as follows:

1. Open the system settings or control center from your application menu.
2. Look for a category related to “Software” or “Applications.”
3. Locate the section that displays information about installed software or packages.
4. Search for Java-related entries, which often include version information.

A Walkthrough of Using a Graphical Tool

The specific steps for using graphical tools may vary based on your Linux distribution. Therefore, it’s advisable to consult your distribution’s documentation or support resources for detailed instructions.

Alternative Methods

Besides the methods mentioned above, there are alternative approaches to determine the Java version installed on your Linux system.

Checking Java Version in the Package Manager

Your Linux package manager can be a valuable resource for finding information about installed software, including Java. Use the following commands to search for Java:

• Debian-based Systems (e.g., Ubuntu)

apt list --installed | grep -i openjdk

• Red Hat-based Systems (e.g., CentOS)

rpm -qa | grep -i openjdk

• Arch Linux

pacman -Q | grep -i jre

Inspecting Environment Variables

Environment variables can provide information about the active Java installation. Specifically, the JAVA_HOME variable points to the Java installation directory, and the PATH variable may include the path to the Java executable. Use the following commands to check these variables:

1. Check JAVA_HOME:

echo $JAVA_HOME

2. Check PATH for Java:

echo $PATH | grep -i java

Exploring the “Alternatives” Command for Advanced Users

For advanced users who need precise control over Java versions, you can explore the “alternatives” system on Debian-based systems like Ubuntu. This allows you to configure which Java version is the default on your system. Use the following commands:

1. List available alternatives:

sudo update-alternatives --list java

2. Configure the default Java version:

sudo update-alternatives --config java

The Role of the /usr/lib/jvm Directory

On many Linux distributions, Java installations are stored in the /usr/lib/jvm directory. You can check this directory for a list of available Java installations.

1. Open a terminal.

2. Navigate to the /usr/lib/jvm directory:

cd /usr/lib/jvm

3. List the contents of the directory:

ls

This will show you the available Java installations and their respective directories. You can then check the version of a specific installation by examining its contents.

Troubleshooting Common Issues

Checking your Java version can sometimes reveal issues with your installation. Here are some common problems and how to address them:

Handling Multiple Java Installations

If you have multiple Java installations on your system, you might encounter conflicts or issues with the default version. To resolve this:

1. Use the “update-alternatives” command on Debian-based systems to set the desired default Java version.
2. Modify the PATH and JAVA_HOME environment variables to point to the desired Java installation directory.
3. Uninstall unnecessary Java versions using your package manager.

Fixing Environment Variable Conflicts

Conflicting environment variables can lead to unexpected behavior. To resolve conflicts:

1. Check the JAVA_HOME and PATH variables for inconsistencies and correct them.
2. Remove any environment variable settings that point to non-existent or conflicting Java installations.

Best Practices for Managing Java on Linux

Ensuring you have the correct Java version on your Linux system is essential for a smooth experience. Here are some best practices for managing Java:

Installing and Updating Java

• Use your distribution’s package manager to install or update Java. This ensures compatibility with your system and simplifies future updates.

Uninstalling Unwanted Java Versions

• Regularly check your system for outdated or unused Java installations. Use your package manager to remove them.

Setting the Default Java Version

• On Debian-based systems, use the “update-alternatives” command to configure the default Java version. This ensures that system-wide applications use the desired Java version.

Regularly Checking for Updates

• Keep your Java installations up to date by regularly updating your system using your package manager. This ensures you have the latest security patches and bug fixes.

Conclusion

In this comprehensive guide, we’ve explored various methods for checking the Java version installed on your Linux system. Whether you prefer the command line or graphical tools, you now have the knowledge to identify your Java installation and manage it effectively. Additionally, we’ve covered troubleshooting common issues and provided best practices for maintaining your Java installations.

By following the steps outlined in this guide, you can ensure that your Linux system is equipped with the right Java version for your needs, whether you’re a developer or a casual user.