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This page documents how to develop ITK through Git. See our table of contents for more information.

Git is an extremely powerful version control tool that supports many different "workflows" for indivudal development and collaboration. Here we document procedures used by the ITK development community. In the interest of simplicity and brevity we do not provide an explanation of why we use this approach. Furthermore, this is not a Git tutorial. Please see our Git resource links for third-party documentation, such as the ProGit Book.


Before you begin, perform initial setup:

1. Register Gerrit access and possibly Git push access.

2. Optionally download our one page PDF desk reference.

3. Follow the download instructions to create a local ITK clone:

$ git clone git://

Connection refused?

4. Run the developer setup script to prepare your ITK work tree and create Git command aliases used below:

$ ./Utilities/
Pro Git: Setup

Note that if you answer 'y' to the question "Do you want to test push access to [y/N]:", you will most likely receive the following error message: "Permission denied (publickey). fatal: Could not read from remote repository.". Only a few experienced contributors have push access. Having push access is not necessary to contribute to ITK.


ITK development uses a branchy workflow based on topic branches. Our collaboration workflow consists of three main steps:

1. Local Development

2. Code Review

Gerrit Code Review

3. Integrate Changes


Update your local master branch:

$ git checkout master
$ git pullall

git help checkout
(pull and submodule update)

Create a Topic

All new work must be committed on topic branches. Name topics like you might name functions: concise but precise. A reader should have a general idea of the feature or fix to be developed given just the branch name.

To start a new topic branch:

$ git fetch origin

For new development, start the topic from origin/master:

$ git checkout -b my-topic origin/master

For release branch fixes, start the topic from origin/release, and by convention use a topic name starting in "release-":

$ git checkout -b my-topic origin/release

git help fetch
git help checkout
git help submodule
Pro Git: Basic Branching

Edit files and create commits (repeat as needed). Add a prefix to your commit message (see below).

$ edit file1 file2 file3
(To add data follow these instructions.)
$ git add file1 file2 file3
$ git commit

git help add
git help commit
Pro Git: Recording Changes

(If your change modifies the "Modules/ThirdParty/KWSys/src/KWSys" directory please contribute directly to KWSys instead.)
(If your change modifies the "Modules/ThirdParty/MetaIO/src/MetaIO" directory please contribute directly to MetaIO instead.)

Standard prefixes for ITK commit messages :

  • BUG: Fix for runtime crash or incorrect result
  • COMP: Compiler error or warning fix
  • DOC: Documentation change
  • ENH: New functionality
  • PERF: Performance improvement
  • STYLE: No logic impact (indentation, comments)
  • WIP: Work In Progress not ready for merge

Share a Topic

When a topic is ready for review and possible inclusion, share it by pushing to Gerrit. Be sure you have registered for Gerrit access.

Checkout the topic if it is not your current branch:

$ git checkout my-topic

git help checkout

Check what commits will be pushed to Gerrit for review:

$ git prepush

(log origin/master..)

Push commits in your topic branch for review by the community:

$ git gerrit-push
(If the topic adds data see this note.)

or if you started the topic from the release branch:

$ git push gerrit HEAD:refs/for/release/my-topic

Connection refused?

Find your change in the ITK Gerrit instance and add reviewers.

Revise a Topic

If a topic is approved during Gerrit review, skip to the next step. Otherwise, revise the topic and push it back to Gerrit for another review.

Checkout the topic if it is not your current branch:

$ git checkout my-topic

git help checkout

To revise the most recent commit on the topic edit files and add changes normally and then amend the commit:

$ git commit --amend

git help commit
Pro Git: Changing the Last Commit

To revise commits further back on the topic, say the 3rd commit back:

$ git rebase -i HEAD~3

(Substitute the correct number of commits back, as low as 1.)

Follow Git's interactive instructions. Preserve the Change-Id: line at the bottom of each commit message.

git help rebase
Pro Git: Changing Multiple Commits
Pro Git: Rebasing

Return to the previous step to share the revised topic.

Test a Topic

When a patch is submitted, it is tested across the three major platforms before being merged and tested on many platforms and configurations on the nightly dashboard.

If tests fail on a submitted topic, see the previous step on how to submit a revised version. After a topic is merged, please check the next day's nightly dashboard to ensure there are not any regressions. If there are any new warnings or errors, submit a follow-up patch as soon as possible.

When a patch is submitted, MacOSX-Clang, Windows-MSVC, and Linux-GCC builds will start. Once they have finished, the build robots will make a comment on the patch with a link to their results visualized in CDash and mark the patch set as Verified +1 or Not Verified -1. The results are submitted by the Kitware Build Robot Gerrit user.

Builds can be spawned by adding the following comments to a patch set in Gerrit.

request build: all

MacOSX, Linux, Windows

request build: osx


request build: linux


request build: windows


request build: python

Python Wrapping (Linux, MacOSX, Windows)

request build: power8


request build: cpp11

C++11 (Linux, MacOSX, Windows)

request build: cpp14

C++14 (Linux, MacOSX, Windows)

request build: cpp17

C++17 (Linux, MacOSX, Windows)

Merge a Topic

Only authorized developers with Git push access to may perform this step.

After a feature topic has been reviewed and approved in Gerrit, merge it into the upstream repository.

Checkout the topic if it is not your current branch:

$ git checkout my-topic

git help checkout

Merge the topic, which is originally forked off the master branch, to master branch:

$ git gerrit-merge
(If the merge conflicts follow the printed instructions to resolve them.)

(push to topic stage and
stage ITK merge my-topic)
Branch-to-Topic Conflict Resolution

For bug fixes that are ready to be included in the next patch release, please email the release manager, Matt McCormick, for assistance.

Here are the recommended steps to merge a topic to both release and master branches, assuming the topic branch is forked off the release branch:

$ git checkout release
$ git merge --no-ff my-topic
$ git push origin release

and do:

$ git checkout master
$ git merge --no-ff release
$ git push origin master

to merge the release branch back to master.

Delete a Topic

After a topic has been merged upstream, delete your local branch for the topic.

Checkout and update the master branch:

$ git checkout master
$ git pullall

git help checkout
(pull and submodule update)

Delete the local topic branch:

$ git branch -d my-topic

git help branch

The branch -d command works only when the topic branch has been correctly merged. Use -D instead of -d to force the deletion of an unmerged topic branch (warning - you could lose commits).