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OpenJDK Project Skara

The goal of Project Skara is to investigate alternative SCM and code review options for the OpenJDK source code, including options based upon Git rather than Mercurial, and including options hosted by third parties.

This repository contains tooling for working with OpenJDK projects and their repositories. The following CLI tools are available as part of this repository:

  • git-jcheck - a backwards compatible Git port of jcheck
  • git-webrev - a backwards compatible Git port of webrev
  • git-defpath - a backwards compatible Git port of defpath
  • git-fork - fork a project on an external Git source code hosting provider to your personal space and optionally clone it
  • git-sync - sync the personal fork of the project with the current state of the upstream repository
  • git-pr - interact with pull requests for a project on an external Git source code hosting provider
  • git-info - show OpenJDK information about commits, e.g. issue links, authors, contributors, etc.
  • git-token - interact with a Git credential manager for handling personal access tokens
  • git-translate - translate between Mercurial and Git hashes
  • git-skara - learn about and update the Skara CLI tools
  • git-trees - run a git command in a tree of repositories
  • git-publish - publishes a local branch to a remote repository
  • git-backport - backports a commit from another repository onto the current branch

There are also CLI tools available for importing OpenJDK Mercurial repositories into Git repositories and vice versa:

  • git-openjdk-import
  • git-verify-import
  • hg-openjdk-import

The following server-side tools (so called "bots") for interacting with external Git source code hosting providers are available:

  • hgbridge - continuously convert Mercurial repositories to git
  • mlbridge - bridge messages between mailing lists and pull requests
  • notify - send email notifications when repositories are updated
  • pr - add OpenJDK workflow support for pull requests
  • submit - example pull request test runner
  • forward - forward commits to various repositories
  • mirror - mirror repositories
  • merge - merge commits between different repositories and/or branches
  • test - test runner


JDK 17 or later and Gradle 7.2 or later is required for building. To build the project on macOS or GNU/Linux x64, just run the following command from the source tree root:

$ sh gradlew

To build the project on Windows x64, run the following command from the source tree root:

> gradlew

The extracted jlinked image will end up in the build directory in the source tree root. Note that the above commands will build the CLI tools, if you also want to build the bot images run sh gradlew images on GNU/Linux or gradlew images on Windows.

Other operating systems and CPU architectures

If you want to build on an operating system other than GNU/Linux, macOS or Windows or if you want to build on a CPU architecture other than x64, then ensure that you have JDK 17 or later installed locally and JAVA_HOME set to point to it. You can then run the following command from the source tree root:

$ sh gradlew

The extracted jlinked image will end up in the build directory in the source tree root.

Offline builds

If you don't want the build to automatically download any dependencies, then you must ensure that you have installed the following software locally:

  • JDK 17 or later
  • Gradle 7.2 or later

To create a build then run the command:

$ gradle offline

Please note that the above command does not make use of gradlew to avoid downloading Gradle.

The extracted jlinked image will end up in the build directory in the source tree root.


It is also supported to cross-jlink jimages to GNU/Linux, macOS and/or Windows from any of the aforementioned operating systems. To build all applicable jimages (including the server-side tooling), run the following command from the source tree root:

sh gradlew images

Makefile wrapper

Skara also has a very thin Makefile wrapper for contributors who prefer to build using make. To build the jlinked image for the CLI tools using make, run:



There are multiple way to install the Skara CLI tools. The easiest way is to just include skara.gitconfig in your global Git configuration file. You can also install the Skara tools on your $PATH.

Including skara.gitconfig

To install the Skara tools, include the skara.gitconfig Git configuration file in your user-level Git configuration file. On macOS or GNU/Linux:

$ git config --global include.path "$PWD/skara.gitconfig"

On Windows:

> git config --global include.path "%CD%/skara.gitconfig"

To check that everything works as expected, run the command git skara help.

Adding to PATH

The Skara tools can also be added to $PATH on GNU/Linux and macOS and Git will pick them up. You can either just extend $PATH with the build/bin directory or you can copy the tools to a location already on $PATH. To extend $PATH with the build/bin directory, run:

$ sh gradlew
$ export PATH="$PWD/build/bin:$PATH"

To copy the tools to a location already on $PATH, run:

$ make
$ make install prefix=/path/to/install/location

When running make install the default value of prefix is $HOME/.local.

If you want git help <skara tool> (or the equivalent man git-<skara tool> to work, you must also add the build/bin/man directory to $MANPATH. For instance, run this from the Skara top directory to add this to your .bashrc file:

echo "export MANPATH=\$MANPATH":$PWD/build/bin/man >> ~/.bashrc


JUnit 5.8.2 or later is required to run the unit tests. To run the tests, execute following command from the source tree root:

$ sh gradlew test

If you prefer to use the Makefile wrapper you can also run:

$ make test

The tests expect Git version 2.19.3 or later and Mercurial 4.7.2 or later to be installed on your system.

This repository also contains a Dockerfile, test.dockerfile, that allows for running the tests in a reproducible way with the proper dependencies configured. To run the tests in this way, run the following command from the source tree root:

$ sh gradlew reproduce

If you prefer to use the Makefile wrapper you can also run:

$ make reproduce


There are no additional dependencies required for developing Skara if you can already build and test it (see above for instructions). The command-line tools and libraries supports all of GNU/Linux, macOS and Windows and can therefore be developed on any of those operating systems. The bots primarily support macOS and GNU/Linux and may require Windows Subsystem for Linux on Windows.

Please see the sections below for instructions on setting up a particular editor or IDE.

IntelliJ IDEA

If you choose to use IntelliJ IDEA as your IDE when working on Skara you can simply open the root folder and the project should be automatically imported. You will need to configure a Platform SDK that is JDK 17 or above. Either set this up manually, or build once from the terminal, which will download a suitable JDK. Configure IntelliJ to use it at File → Project Structure → Platform Settings → SDKs → + → Add JDK... and browse to the downloaded JDK found in <skara-folder>/.jdk/. For example, on macOS, select the <skara-folder>/.jdk/openjdk-17_osx-x64_bin/jdk-17.jdk/Contents/Home folder.


If you choose to use Vim as your editor when working on Skara then you probably also want to utilize the Makefile wrapper. The Makefile wrapper enables to you to run :make and :make tests in Vim.


Project Skara's wiki is available at


Issues are tracked in the JDK Bug System under project Skara at


We are more than happy to accept contributions to the Skara tooling, both via patches sent to the Skara mailing list and in the form of pull requests on GitHub.


See for the current Skara Reviewers, Committers and Authors. See for how to become an author, committer or reviewer in an OpenJDK project.


Development discussions take place on the project Skara mailing list, see for instructions on how to subscribe of if you want to read the archives. You can also reach many project Skara developers in the #openjdk IRC channel on OFTC, see for details.


See the file LICENSE for details.