# How to Check Java Version in Linux Checking your Java version on a Linux system is a common task for developers and system administrators. Whether you’re setting up a new environment, troubleshooting software, or ensuring compatibility, knowing which Java version is installed is essential. In this article, I’ll guide you through easy methods to find your Java version on Linux, using commands and environment variables. You might think this is complicated, but it’s actually straightforward. I’ll explain step-by-step how to check your Java version, including how to verify both the Java Runtime Environment (JRE) and Java Development Kit (JDK). By the end, you’ll be confident in managing Java versions on your Linux machine. ## Why Checking Java Version Matters on Linux Java is a popular programming language and platform used in many applications. Different programs require different Java versions, so it’s important to know what you have installed. Here’s why checking your Java version on Linux is useful: - **Compatibility:** Some applications need specific Java versions to run correctly. - **Security:** Older Java versions may have vulnerabilities; updating helps keep your system safe. - **Development:** Developers need to confirm the JDK version to compile and run Java programs. - **Troubleshooting:** Knowing the Java version helps diagnose issues related to Java applications. Linux users often have multiple Java versions installed, so checking which one is active is crucial. Let’s explore how to do this easily. ## How to Check Java Version Using the Terminal The most common way to check your Java version on Linux is through the terminal. This method works on most Linux distributions like Ubuntu, Fedora, CentOS, and Debian. ### Step 1: Open Your Terminal You can open the terminal by searching for “Terminal” in your applications menu or pressing `Ctrl + Alt + T` on most Linux desktops. ### Step 2: Run the Java Version Command Type the following command and press Enter: ```bash java -version ``` This command tells the system to display the installed Java runtime version. ### What You’ll See The output looks something like this: ``` openjdk version "17.0.5" 2026-04-20 OpenJDK Runtime Environment (build 17.0.5+10) OpenJDK 64-Bit Server VM (build 17.0.5+10, mixed mode) ``` This output shows the Java version installed (OpenJDK 17.0.5 in this example). If you see an error like `command not found`, Java might not be installed or not added to your system’s PATH. ### Checking the JDK Version If you want to check the Java Development Kit (JDK) version, use: ```bash javac -version ``` This command shows the version of the Java compiler, which is part of the JDK. For example: ``` javac 17.0.5 ``` If this command fails, it means the JDK is not installed, or the `javac` command is not in your PATH. ## How to Check Java Version Using Environment Variables Sometimes, Java is installed but not set as the default version. You can check environment variables to see which Java version your system uses. ### Step 1: Check JAVA_HOME Variable The `JAVA_HOME` environment variable points to the Java installation directory. To check it, run: ```bash echo $JAVA_HOME ``` If this returns a path like `/usr/lib/jvm/java-17-openjdk-amd64`, it shows where Java is installed. ### Step 2: Verify the Java Binary Path You can also check which Java binary is used by default with: ```bash which java ``` This command returns the path to the Java executable, for example: ``` /usr/bin/java ``` You can then check the version of this Java binary by running: ```bash /usr/bin/java -version ``` This helps confirm the exact Java version your system uses when you run Java commands. ## Managing Multiple Java Versions on Linux Linux systems often have multiple Java versions installed. You can switch between them using tools like `update-alternatives` on Debian-based systems. ### Using update-alternatives to Switch Java Versions 1. List all installed Java versions: ```bash sudo update-alternatives --config java ``` 2. You’ll see a list like this: ``` There are 3 choices for the alternative java (providing /usr/bin/java). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1111 auto mode 1 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode 2 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1111 manual mode 3 /usr/lib/jvm/java-17-openjdk-amd64/bin/java 1200 manual mode ``` 3. Enter the number corresponding to the Java version you want to use and press Enter. 4. Verify the change by running: ```bash java -version ``` This method lets you switch Java versions without uninstalling any. ## Installing Java on Linux If Not Installed If your system doesn’t have Java installed, you can easily add it. ### Installing OpenJDK on Ubuntu/Debian ```bash sudo apt update sudo apt install openjdk-17-jdk ``` ### Installing OpenJDK on Fedora/CentOS ```bash sudo dnf install java-17-openjdk-devel ``` After installation, check the version again with `java -version`. ## Troubleshooting Common Issues When Checking Java Version Sometimes, you might face issues when checking your Java version. Here are common problems and fixes: - **Command not found:** Java is not installed or not in PATH. Install Java or add it to PATH. - **Wrong version showing:** Multiple Java versions installed; switch using `update-alternatives`. - **JAVA_HOME not set:** Set the variable in your shell profile (`~/.bashrc` or `~/.zshrc`): ```bash export JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64 export PATH=$JAVA_HOME/bin:$PATH ``` Reload the profile with `source ~/.bashrc`. ## Summary Table: Commands to Check Java Version on Linux | Command | Purpose | Example Output | |--------------------------|---------------------------------|----------------------------------| | `java -version` | Check Java Runtime Environment | `openjdk version "17.0.5"` | | `javac -version` | Check Java Development Kit | `javac 17.0.5` | | `echo $JAVA_HOME` | Show Java installation path | `/usr/lib/jvm/java-17-openjdk-amd64` | | `which java` | Show path to Java executable | `/usr/bin/java` | | `sudo update-alternatives --config java` | Switch Java versions | List of installed Java versions | ## Conclusion Now you know how to check your Java version on Linux quickly and easily. Whether you use the `java -version` command or check environment variables like `JAVA_HOME`, these methods help you understand your Java setup. You can also manage multiple Java versions using `update-alternatives` to ensure your system runs the right Java for your needs. Keeping your Java version updated and knowing which one is active is key for security, compatibility, and development. Next time you need to verify Java on your Linux machine, just open your terminal and follow these simple steps. You’ll be ready to handle any Java-related task with confidence. ### FAQs #### How do I check if Java is installed on Linux? Run `java -version` in the terminal. If Java is installed, it shows the version. If not, you’ll get a “command not found” error. #### What is the difference between `java -version` and `javac -version`? `java -version` shows the Java Runtime Environment version, while `javac -version` shows the Java compiler version, part of the JDK. #### How can I switch between multiple Java versions on Linux? Use `sudo update-alternatives --config java` to select the active Java version from installed options. #### What does the `JAVA_HOME` environment variable do? `JAVA_HOME` points to the directory where Java is installed. It helps programs find Java binaries and libraries. #### How do I set the `JAVA_HOME` variable permanently? Add `export JAVA_HOME=/path/to/java` and `export PATH=$JAVA_HOME/bin:$PATH` to your shell profile file like `~/.bashrc`, then run `source ~/.bashrc`.