Introduction to OpenJDK

OpenJDK is an open-source implementation of Oracle's Java Standard Edition platform. OpenJDK is useful for developing Java programs, and provides a complete runtime environment to run Java programs.

This package is known to build and work properly using an LFS 12.1 platform.

OpenJDK is GPL'd code, with a special exception made for non-free projects to use these classes in their proprietary products. In similar fashion to the LGPL, which allows non-free programs to link to libraries provided by free software, the GNU General Public License, version 2, with the Classpath Exception allows third party programs to use classes provided by free software without the requirement that the third party software also be free. As with the LGPL, any modifications made to the free software portions of a third party application, must also be made freely available.



The OpenJDK source includes a very thorough, open source test suite using the JTreg test harness. The testing instructions below allow testing the just built JDK for reasonable compatibility with the proprietary Oracle JDK. However, in order for an independent implementation to claim compatibility, it must pass a proprietary JCK/TCK test suite. No claims of compatibility, or even partial compatibility, may be made without passing an approved test suite.

Oracle does provide free community access, on a case-by-case basis, to a closed toolkit to ensure 100% compatibility with its proprietary JDK. Neither the binary version provided on the Java-21.0.2 page nor the JVM built with the instructions below have been tested against the TCK. Any version that is built using the instructions given, cannot claim to be compatible with the proprietary JDK, without the user applying for, and completing the compatibility tests themselves.

With that in mind, the binaries produced using this build method are regularly tested against the TCK by the members listed on the site above. In addition to the community license above, an educational, non-commercial license for the TCK can be obtained here.

Package Information

Additional Downloads

Optional test harness

OpenJDK Dependencies

Required Dependencies

An existing binary (Java-21.0.2 or an earlier built version of this package. The instructions below assume that you are using Configuring the Java environment), alsa-lib-1.2.11, cpio-2.15, Cups-2.4.7, UnZip-6.0, Which-2.21, Xorg Libraries, and Zip-3.0



git-2.44.0, Graphviz-10.0.1, Mercurial-6.6.3, ccache, pandoc, and pigz

Installation of OpenJDK

If you have downloaded the optional test harness, unpack it now:

tar -xf ../jtreg-7.3.1+1.tar.gz


Before proceeding, you should ensure that your environment PATH variable contains the location of the Java compiler used for bootstrapping OpenJDK. This is the only requirement for the environment. Modern Java installations do not need JAVA_HOME and CLASSPATH is not used here. Furthermore, OpenJDK developers recommend unsetting JAVA_HOME.

The build system does not allow the -j switch in MAKEFLAGS. See the command explanation for --with-jobs= for more information on customizing parallelization.

Configure and build the package with the following commands:

unset JAVA_HOME                             &&
bash configure --enable-unlimited-crypto    \
               --disable-warnings-as-errors \
               --with-stdc++lib=dynamic     \
               --with-giflib=system         \
               --with-harfbuzz=system       \
               --with-jtreg=$PWD/jtreg      \
               --with-lcms=system           \
               --with-libjpeg=system        \
               --with-libpng=system         \
               --with-zlib=system           \
               --with-version-build="13"    \
               --with-version-pre=""        \
               --with-version-opt=""        \
               --with-cacerts-file=/etc/pki/tls/java/cacerts &&
make images

To test the results, you will need to execute the jtreg program. You can set the number of concurrent tests by adding the -conc:<X> value in the below command (tests will run sequentially otherwise):

export JT_JAVA=$(echo $PWD/build/*/jdk) &&
jtreg/bin/jtreg -jdk:$JT_JAVA -automatic -ignore:quiet -v1 \
    test/jdk:tier1 test/langtools:tier1 &&
unset JT_JAVA

For more control over the test suite, review the documentation available in jtreg/doc/jtreg/usage.txt. To review the results, see the files JTreport/test_{jdk,langtools}/text/stats.txt and JTreport/test_{jdk,langtools}/text/summary.txt. You should expect to see around 60 failures and 10 errors.

Install the package with the following commands as the root user:

install -vdm755 /opt/jdk-21.0.2+13             &&
cp -Rv build/*/images/jdk/* /opt/jdk-21.0.2+13 &&
chown -R root:root /opt/jdk-21.0.2+13          &&
for s in 16 24 32 48; do
  install -vDm644 src/java.desktop/unix/classes/sun/awt/X11/java-icon${s}.png \


If you only wish to install the Java Runtime Environment, you can substitute build/*/images/jre in the above cp command.

There are now two OpenJDK SDKs installed in /opt. You should decide on which one you would like to use as the default. Normally, you would opt for the just installed OpenJDK. If so, do the following as the root user:

ln -v -nsf jdk-21.0.2+13 /opt/jdk

If desired, you can create .desktop files to add entries in the menu for java and jconsole. The needed icons have already been installed. As the root user:

mkdir -pv /usr/share/applications &&

cat > /usr/share/applications/openjdk-java.desktop << "EOF" &&
[Desktop Entry]
Name=OpenJDK Java 21.0.2 Runtime
Comment=OpenJDK Java 21.0.2 Runtime
Exec=/opt/jdk/bin/java -jar
cat > /usr/share/applications/openjdk-jconsole.desktop << "EOF"
[Desktop Entry]
Name=OpenJDK Java 21.0.2 Console
Comment=OpenJDK Java 21.0.2 Console

Command Explanations

bash configure...: the top level configure is a wrapper around the autotools one. It is not executable and must be run through bash.

--enable-unlimited-crypto: Because of limitations on the usage of cryptography in some countries, there is the possibility to limit the size of encryption keys and the use of some algorithms in a policy file. This switch allows to ship a policy file with no restriction. It is the responsibility of the user to ensure proper adherence to the law.

--disable-warnings-as-errors: This switch disables use of -Werror in the build.

--with-stdc++lib=dynamic: This switch forces the build system to link to (dynamic) instead of libstdc++.a (static).

--with-jobs=<X>: The -j passed to make does not work with make as invoked here. By default, the build system will use the number of CPUs - 1.

--with-jtreg=$PWD/jtreg: This switch tells configure where to find jtreg. Omit if you have not downloaded the optional test suite.

--with-{giflib,harfbuzz,lcms,libjpeg,libpng,zlib}=system: These switches force the build system to use the system libraries instead of the bundled versions.

--with-version-build: Currently, the build system does not include the build number in the version string. It has to be specified here.

--with-version-pre: This switch allows you to prefix the version string with a custom string.

--with-version-opt: This switch allows you to add an optional build description to the version string.

--with-cacerts-file=/etc/pki/tls/java/cacerts: Specifies where to find a cacerts file, /etc/pki/tls/java/ on a BLFS system. Otherwise, an empty one is created. You can use the /usr/sbin/make-ca --force command to generate it, once you have installed the Java binaries.

--with-boot-jdk: This switch provides the location of the temporary JDK. It is normally not needed if java is found in the PATH.

Configuring OpenJDK

Configuration Information

Normally, the Java environment has been configured after installing the binary version, and can be used with the just built package as well. Review Configuring the Java environment in case you want to modify something.

To test if the man pages are correctly installed, issue source /etc/profile and man java to display the respective man page.

Setting up the JRE Certificate Authority Certificates (cacerts) file

If you have run the instructions on the make-ca-1.13 page, you only need to create a symlink in the default location for the cacerts file. As user root:

ln -sfv /etc/pki/tls/java/cacerts /opt/jdk/lib/security/cacerts

To check the installation, issue:

cd /opt/jdk
bin/keytool -list -cacerts

At the prompt Enter keystore password:, enter changeit (the default) or just press the Enter key. If the cacerts file was installed correctly, you will see a list of the certificates with related information for each one. If not, you need to reinstall them.


Installed Programs: jar, jarsigner, java, javac, javadoc, javap, jcmd, jconsole, jdb, jdeprscan, jdeps, jfr, jhsdb, jimage, jinfo, jlink, jmap, jmod, jpackage, jps, jrunscript, jshell, jstack, jstat, jstatd, jwebserver, keytool, rmiregistry, and serialver
Installed Libraries: 37 libraries in /opt/jdk-21.0.2+13/lib/
Installed Directory: /opt/jdk-21.0.2+13

Short Descriptions


combines multiple files into a single jar archive


signs jar files and verifies the signatures and integrity of a signed jar file


launches a Java application by starting a Java runtime environment, loading a specified class and invoking its main method


reads class and interface definitions, written in the Java programming language, and compiles them into bytecode class files


parses the declarations and documentation comments in a set of Java source files and produces a corresponding set of HTML pages describing the classes, interfaces, constructors, methods, and fields


disassembles a Java class file


is a utility to send diagnostic command requests to a running Java Virtual Machine


is a graphical console tool to monitor and manage both local and remote Java applications and virtual machines


is a simple command-line debugger for Java classes


scans class or jar files for uses of deprecated API elements


shows the package-level or class-level dependencies of Java class files


is a tool for working with Flight Recorder files


is a tool to analyze the content of a core dump from a crashed Java Virtual Machine (JVM)


is used to list, extract, verify, or get information about modules in jimage format


prints Java configuration information for a given Java process, core file, or a remote debug server


is used to assemble and optimize a set of modules and their dependencies into a custom runtime image


prints shared object memory maps or heap memory details of a given process, core file, or a remote debug server


creates JMOD files and lists the content of existing JMOD files


generates java application packages and images


lists the instrumented JVMs on the target system


is a command line script shell


is an interactive tool for learning the Java programming language and prototyping Java code


prints Java stack traces of Java threads for a given Java process, core file, or a remote debug server


displays performance statistics for an instrumented JVM


is an RMI server application that monitors for the creation and termination of instrumented JVMs


provides a minimal HTTP server, designed to be used for prototyping, testing, and debugging


is a key and certificate management utility


creates and starts a remote object registry on the specified port on the current host


returns the serialVersionUID for one or more classes in a form suitable for copying into an evolving class