Synching a git fork

This post is about to sync a fork of a repository to keep it up-to-date with the upstream (the fork base) repository.

The Setup

Before you can sync, you need to add a remote that points to the upstream repository. You may have done this when you originally forked.

Tip: Syncing your fork only updates your local copy of the repository; it does not update your repository on GitHub.

# List the current remotes
$ git remote -v
origin  https://github.com/user/repo.git (fetch)
origin  https://github.com/user/repo.git (push)
# Set a new remote
$ git remote add upstream https://github.com/otheruser/repo.git
# Verify new remote
$ git remote -v
origin    https://github.com/user/repo.git (fetch)
origin    https://github.com/user/repo.git (push)
upstream  https://github.com/otheruser/repo.git (fetch)
upstream  https://github.com/otheruser/repo.git (push)

Syncing

There are two steps required to sync your repository with the upstream: first you must fetch from the remote, then you must rebase or merge the desired branch into your local branch.

Fetching

Fetching from the remote repository will bring in its branches and their respective commits. These are stored in your local repository under special branches.

# Fetch all the branches of that remote into remote-tracking branches,
# such as upstream/master:
$ git fetch upstream
# Make sure that you're on your master branch:
git checkout master

We now have the upstream's master branch stored in a local branch, upstream/master

# List all local and remote-tracking branches
$ git branch -va
* master                  a422352 My local commit
  remotes/origin/HEAD     -> origin/master
  remotes/origin/master   a422352 My local commit
  remotes/upstream/master 5fdff0f Some upstream commit

Rebase

Last step is to rebase your branch and push the changes to your branch.

# rebase
git rebase upstream/master
# push changes to github
git push -f origin master

You only need to use the -f the first time after you've rebased.

If you don't want to rewrite the history of your master branch, (for example because other people may have cloned it) then you should replace the last command with git merge upstream/master. However, for making further pull requests that are as clean as possible, it's probably better to rebase.