Install OpenJDK on Ubuntu Server

This article is for those looking for a detailed and straightforward guide on installing OpenJDK on Ubuntu Server.

NOTE

With the release of Java 11, Oracle JDK became commercial and is no longer free.

OpenJDK is an open-source implementation of the Java Standard Edition platform with contributions from Oracle and the Java open community. The Oracle JDK build process is built from the OpenJDK source, so there isn’t much difference between Oracle JDK and OpenJDK.

NOTE

OpenJDK is free but will need to be updated every 6 months.

IMPORTANT

OpenSSH must be installed on the server, and port 22 must be open in order to be able to connect to the server using the SSH protocol.

To install OpenSSH on a server, you can use the command:

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sudo apt install openssh-server

NOTE

This guide walks you through connecting to a server with the iTerm2 terminal emulator on macOS.

We connect to the server on which you plan to install OpenJDK.

Update the local package index to the latest changes in the repositories using the command:

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sudo apt update

You may need a Java Development Kit (JDK) in addition to the JRE in order to compile and run certain Java-based software.

To install the JDK, run the following command, which will also install the JRE:

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sudo apt-get install -y default-jdk

Now you need to make sure that OpenJDK is installed correctly. To do this, you need to run the command:

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java -version

Based on the message received, OpenJDK is installed correctly.

Many programs written with Java use the “JAVA_HOME” environment variable to determine where Java is installed. Therefore, you need to define this variable and assign it a value containing the path to the Java installation location.

Let’s define the path to the Java installation location using the command:

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sudo update-alternatives --config java

In this example, the path to the Java installation location looks like this:

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/usr/lib/jvm/java-11-openjdk-amd64/bin/

In order to define an environment variable and assign a value to it, you need to make changes to the “environment” file by opening it in a text editor using the command:

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sudo vim /etc/environment

Press the “i” button to switch to edit mode, then at the end of the file define a new variable “JAVA_HOME” and assign it a value containing the path to the Java installation location obtained earlier.

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

NOTE

The path to the Java installation location must be specified up to and including the “bin” folder.

Now press the “Esc” button to exit edit mode, then type "" and press the “Enter” button to save your changes and exit the editor.

Next, you need to apply the changes made to the current session using the command:

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source /etc/environment

Now let’s make sure that the environment variable has the correct value using the command:

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echo $JAVA_HOME

Based on the message received, the environment variable has the correct value.