Configuring OpenJDK 8 for RHEL

OpenJDK 8

Red Hat Customer Content Services

Abstract

OpenJDK is a Red Hat offering on the Red Hat Enterprise Linux platform. The Configuring OpenJDK 8 on RHEL guide provides an overview of this product and explains how to configure the software.

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Chapter 1. Interactively selecting a system-wide OpenJDK version on RHEL

If you have multiple versions of OpenJDK installed on RHEL, you can interactively select the default OpenJDK version to use system-wide.

Note

If you do not have root privileges, you can select an OpenJDK version by configuring the JAVA_HOME environment variable.

Prerequisites

  • You must have root privileges on the system.
  • Multiple versions of OpenJDK were installed using the yum package manager.

Procedure

  1. View the OpenJDK versions installed on the system.

    $ yum list installed "java*"

    A list of installed Java packages appears. 

    Installed Packages
java-1.8.0-openjdk.x86_64                     1:1.8.0.242.b08-0.el8_1                     @rhel-8-appstream-rpms
java-1.8.0-openjdk-headless.x86_64            1:1.8.0.242.b08-0.el8_1                     @rhel-8-appstream-rpms
java-11-openjdk.x86_64                        1:11.0.6.10-0.el8_1                         @rhel-8-appstream-rpms
java-11-openjdk-headless.x86_64               1:11.0.6.10-0.el8_1                         @rhel-8-appstream-rpms
javapackages-filesystem.noarch                5.3.0-1.module+el8+2447+6f56d9a6            @rhel-8-appstream-rpms

  2. Display the OpenJDK versions that can be used for a specific java command and select the one to use: 

    $ sudo alternatives --config java
There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
*+ 1           java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el8_1.x86_64/jre/bin/java)
   2           java-11-openjdk.x86_64 (/usr/lib/jvm/java-11-openjdk-11.0.6.10-0.el8_1.x86_64/bin/java)


Enter to keep the current selection[+], or type selection number: 1
    • The current system-wide OpenJDK version is marked with an asterisk.
    • The current OpenJDK version for the specified java command is marked with a plus sign.

  3. Press Enter to keep the current selection or enter the Selection number of the OpenJDK version you want to select followed by the Enter key.

    The default OpenJDK version for the system is the selected version.

  4. Verify that the chosen binary is selected. 

    $ java -version
openjdk version "1.8.0_242"
OpenJDK Runtime Environment (build 1.8.0_242-b08)
OpenJDK 64-Bit Server VM (build 25.242-b08, mixed mode)
    Note

    This procedure configures the java command. Then javac command can be set up in a similar way, but it operates independently.

    If you have OpenJDK installed, alternatives provides more possible selections. In particular, the javac master alternative switches many binaries provided by the -devel sub-package.

    Even if you have OpenJDK installed, java (and other JRE masters) and javac (and other OpenJDK masters) still operate separately, so you can have different selections for JRE and JDK. The alternatives --config java command affects the jre and its associated slaves.

    If you want to change the Java, use the javac alternatives command. The --config javac utility configures the SDK and related slaves. To see all possible masters, use alternatives --list and check all of the java,javac, jre, and sdk masters.

Chapter 2. Non-interactively selecting a system-wide OpenJDK version on RHEL

If you have multiple versions of OpenJDK installed on RHEL, you can select the default OpenJDK version to use system-wide in a non-interactive way. This is useful for administrators who have root privileges on a Red Hat Enterprise Linux system and need to switch the default OpenJDK on many systems in an automated way.

Note

If you do not have root privileges, you can select an OpenJDK version by configuring the JAVA_HOME environment variable.

Prerequisites

  • You must have root privileges on the system.
  • Multiple versions of OpenJDK were installed using the yum package manager.

Procedure

  1. Select the major OpenJDK version to switch to. For example, for OpenJDK 8, use java-1.8.0-openjdk. 

    # PKG_NAME=java-1.8.0-openjdk
# JAVA_TO_SELECT=$(alternatives --display java | grep "family $PKG_NAME" | cut -d' ' -f1)
# alternatives --set java $JAVA_TO_SELECT

  2. Verify that the active OpenJDK version is the one you specified. 

    $ java -version
openjdk version "1.8.0_242"
OpenJDK Runtime Environment (build 1.8.0_242-b08)
OpenJDK 64-Bit Server VM (build 25.242-b08, mixed mode)
    Note

    A similar approach can be followed for javac.

Chapter 3. Selecting an installed OpenJDK version for a specific application

Some applications require a specific OpenJDK version to run. If multiple versions of OpenJDK are installed on the system using the yum package manager or portable bundle, you can select a OpenJDK version for each application where necessary by setting the value of the JAVA_HOME environment variable or using a wrapper script.

Prerequisites

  • Multiple versions of OpenJDK installed on the machine.
  • Ensure that the application you want to run is installed.

Procedure

  1. Set the JAVA_HOME environment variable. For example, if openjdk-8 was installed using yum:

    $ JAVA_HOME=/usr/lib/jvm/java-8-openjdk

    Note

    The symbolic link java-8-openjdk is controlled by the alternatives command.

  2. Do one of the following:

    • Launch the application using the default, system-wide configuration. 

      $ mvn --version
Apache Maven 3.5.4 (Red Hat 3.5.4-5)
Maven home: /usr/share/maven
Java version: 1.8.0_242, vendor: Oracle Corporation, runtime: /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el8_1.x86_64/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "4.18.0-147.3.1.el8_1.x86_64", arch: "amd64", family: "unix"

    • Launch the application specifying the JAVA_HOME variable: 

      $ JAVA_HOME=/usr/lib/jvm/java-8-openjdk mvn --version

Apache Maven 3.5.4 (Red Hat 3.5.4-5)
Maven home: /usr/share/maven
Java version: 1.8.0_242, vendor: Oracle Corporation, runtime: /usr/lib/jvm/java-8-openjdk-1.8.0.242.b08-0.el8_1.x86_64
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "5.4.12-200.el8_1.x86_64", arch: "amd64", family: "unix"

Chapter 4. Selecting a system-wide archive OpenJDK version

If you have multiple versions of OpenJDK installed with the archive on RHEL 8, you can select a specific OpenJDK version to use system-wide.

Prerequisites

  • Know the locations of the OpenJDK versions installed using the archive.

Procedure

To specify the OpenJDK version to use for a single session:

  1. Configure JAVA_HOME with the path to the OpenJDK version you want used system-wide.

    $ export JAVA_HOME=/opt/jdk/jdk-1.8.0

  2. Add $JAVA_HOME/bin to the PATH environment variable.

    $ export PATH="$JAVA_HOME/bin:$PATH"

To specify the OpenJDK version to use permanently for a single user, add these commands into ~/.bashrc: 

export JAVA_HOME=/opt/jdk/jdk-1.8.0
export PATH="$JAVA_HOME/bin:$PATH"

To specify the OpenJDK version to use permanently for all users, add these commands into /etc/bashrc: 

export JAVA_HOME=/opt/jdk/jdk-1.8.0
export PATH="$JAVA_HOME/bin:$PATH"
Note

If you do not want to redefine JAVA_HOME, add only the PATH command to bashrc, specifying the path to the Java binary. For example, export PATH="/opt/jdk/jdk-1.8.0/bin:$PATH"

Additional resources

Chapter 5. Configuring the JAVA_HOME environment variable on RHEL

Some applications require you to set the JAVA_HOME environment variable so that they can find the OpenJDK installation.

Prerequisites

  • You know where you installed OpenJDK on your system. For example, /opt/jdk/11.

Procedure

  1. Set the value of JAVA_HOME. 

    $ export JAVA_HOME=/opt/jdk/11

  2. Verify that JAVA_HOME is set correctly. 

    $ printenv | grep JAVA_HOME
JAVA_HOME=/opt/jdk/11
    Note

    You can make the value of JAVA_HOME persistent by exporting the environment variable in ~/.bashrc for single users or /etc/bashrc for system-wide settings. Persistent means that if you close your terminal or reboot your computer, you do not need to reset a value for the JAVA_HOME environment variable.

    The following example demonstrates using a text editor to enter commands for exporting JAVA_HOME in ~/.bashrc for a single user: 

    > vi ~/.bash_profile

export JAVA_HOME=/opt/jdk/11
export PATH="$JAVA_HOME/bin:$PATH"

Additional resources

Chapter 6. Configuring the heap size for OpenJDK application on RHEL

You can configure OpenJDK to use a customized heap size.

Procedure

  • Add the maximum heap size option to the java command when running your application. For example, to set the maximum heap size to 100 megabytes, use the -Xmx100m option: 

    $ java -Xmx100m <your_application_name>

Additional resources

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