Jdk path is a valid jdk root folder linux

If you are running Java programs on Ubuntu using Eclipse, Maven or Netbeans etc, you’ll need to set JAVA_HOME to your path. Otherwise, your system will complain that “java_home environment variable is not set”.

In this beginner’s tutorial, I’ll show the steps to correctly set Java Home variable on Ubuntu. The steps should be valid for most other Linux distributions as well.

The process consists of these steps:

• Making sure Java Development Kit (JDK) is installed.
• Finding the correct location of JDK executable.
• Setting the JAVA_HOME variable and making the change permanent.

Step 1: Check if JDK is installed

The simplest way to check if Java Development Kit (JDK) is installed on your Linux system is by running this command:

javac --version

The above command checks the version of Java compiler. If it is installed, it will show the Java version.

If the command shows an error like javac command not found, you’ll have to install JDK.

If Java Compiler is not installed on your system, install Java Development Kit using this command:

sudo apt install default-jdk

This will install the default Java version in your current Ubuntu version. If you need some other specific Java version, you’ll have to specify it while installing Java on Ubuntu.

Once you have made sure that Java Compiler is present on your system, it’s time to find its location.

Step 2: Get the location of JDK executable (Java Compiler)

The executable is usually located in the /usr/lib/jvm directory. I won’t left you on your own for a guessing game. Instead, let’s find out the path of the Java executable.

Use the which command to get the location of Java Compiler executable:

which javac

And when you find a path like /usr/lib/jvm/java-11-openjdk-amd64/bin/javac, you remove the /bin/javac from it to get something like /usr/lib/jvm/java-11-openjdk-amd64

readlink -f `which javac` | sed "s:/bin/javac::"

In my example, the location of the executable file is /usr/lib/jvm/java-11-openjdk-amd64. It could be different for you. Copy the correct path you got from the above command in your system. You know, you can copy paste in the Ubuntu terminal.

Step 3: Setting JAVA_HOME variable

Now that you have got the location, use it to set the JAVA_HOME environment variable:

export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64/bin/java

Check the value of JAVA_HOME directory:

echo $JAVA_HOME

Try to run your program or project in the SAME TERMINAL and see if it works.

This is not over yet. The JAVA_HOME variable you just declared is temporary. If you close the terminal or start a new session, it will be empty again.

To set JAVA_HOME variable ‘permanently’, you should add it to the bashrc file in your home directory.

Back up your bashrc file (in case you mess it, you can get it back):

cp ~/.bashrc ~/.bashrc.bak

echo "export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64" >> ~/.bashrc

Verify that it has been correctly added to the end of the file:

tail -3 ~/.bashrc

The above tail command will show the last 3 lines of the specified file.

Here’s the entire output of the above three commands.

Now, even if you exit the session or restart the system, the JAVA_HOME variable will still be set to the value you specified. That’s what you want, right?

Do note that if you change the default Java version in the future, you’ll have to change the value of JAVA_HOME and point it to the correct executable path.

I hope this tutorial not only helped you to set Java Home, it also taught you how you are doing it.

If you are still facing issues or have any questions or suggestions, please let me know in the comments.

Let’s consider a JDK8 installation using 2 different versions: default and Oracle. The default version is easiest because it is packaged with Ubuntu.

There is default Java installation called the JDK (Java Development Kit). The JDK is usually only needed if you are going to to do some software developmwent using Java or if some software requires it. The JDK does contain the JRE.

Installing the default JDK

This will install OpenJDK 8, the latest and recommended version.

First, update the package index:

sudo apt-get install default-jdk

Installing the Oracle JDK

1. Download the latest JDK file

A current link is http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html, if there is no such page you can find it from general download page http://www.oracle.com/technetwork/java/javase/downloads/index.html

The latest version is Java SE Development Kit 8u181.

The archive file for Linux x64 is jdk-8u181-linux-x64.tar.gz

If you download it from web browser, in typical configuration the file will be saved to ~/Downloads directory

2. Open a terminal using Ctrl+Alt+T key combination

3. Change a current directory to ~/Downloads

4. Unpack the tarball

$ tar zxvf jdk-8u181-linux-x64.tar.gz

The Java Development Kit files are installed in a directory called jdk1.8.0_version in the current directory.

You will find a folder with the name as jdk1.8.0_181.

5. Let’s move the directory to default system directory

sudo mv ./jdk1.8.0_181 /usr/lib/jvm

The complete folder “jdk1.8.0_version” will be moved to /usr/lib/jvm.

Delete the .tar.gz file if you want to save disk space.

6. Inform Ubuntu to use this JDK

sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/jdk1.8.0_181/bin/java" 1sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/jdk1.8.0_181/bin/javac" 1sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/jvm/jdk1.8.0_181/bin/javaws" 1

This will assign Oracle JDK a priority of 1, which means that installing other JDKs may replace it as the default. Use a higher priority if you want Oracle JDK to remain the default.

The executables java, javac, javaws are probably the most frequently used.

7. If you have multiple java installations you need to configure it by

sudo update-alternatives --config java

in my case (before this installation, I have installed OpenJDK8), it gives

There are 2 choices for the alternative java (providing /usr/bin/java). Selection Path Priority Status* 0 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 auto mode 1 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode 2 /usr/lib/jvm/jdk1.8.0_181/bin/java 1 manual mode

In this case, I select the last number and press enter to exit this utility i.e. in this example it is the number 2.

If you are going to use javac and javaws, repeat the above for:

sudo update-alternatives --config javacsudo update-alternatives --config javaws

8. Set environment variables

Edit the environment file:

sudo gedit /etc/environment

My current environment file contains:

Update the existing PATH variable by adding the below bin folders, separated with a colon :.

Paths can be different based on version and update, here the version is 1.8 and the update is 181. Add the below variables at the end of environment file, making changes for your specific version and update. I commented out original line.

# 

Save changes and close the file. Log out and log in again.

Verify the Java version

java version "1.8.0_181"Java(TM) SE Runtime Environment (build 1.8.0_181-b13)Java HotSpot(TM) 64-Bit Server VM (build 25.181-b13, mixed mode)

You should be able to see your installed java version which means you have successfully installed the Oracle JDK.