GitHub Fork

Clone, fork, and add upstream remotes so your copy can receive updates without overwriting someone else's default branch.

A fork is GitHub, not git clone

GitHub Repository created a hosted repository you own. A fork is another GitHub repository: GitHub copies someone else's project into your account. git clone is a Git command that copies a URL onto disk. You can clone without forking. You can fork and not clone yet.

Create the hosted copy, then clone it

# GitHub copies the repository into YOUR namespace, then clones that copy
gh repo fork ORIGINAL/REPO --clone
cd REPO
git remote -v

# Typical result after gh repo fork --clone:
# origin    git@github.com:YOU/REPO.git
# upstream  git@github.com:ORIGINAL/REPO.git

gh repo fork ORIGINAL/REPO --clone asks GitHub to copy the repository, then clones the copy. Many setups also add upstream automatically. The website Fork button does the hosted copy only; you still clone the URL under your username.

# Website Fork button, then clone YOUR fork (not the original)
git clone git@github.com:YOU/REPO.git
cd REPO
git remote add upstream git@github.com:ORIGINAL/REPO.git
git remote -v
git fetch upstream

Use a public repository you do not own. Do not fork a private employer project without permission. You can delete a practice fork from GitHub settings when the lab is done.

origin is yours; upstream is theirs

Git Remote taught that a remote is a name plus a URL. A fork clone usually needs two:

Fetch upstream before you change files

git fetch upstream downloads objects and updates remote-tracking names such as upstream/main. It does not merge into your current branch. Read git log --oneline --decorate --graph --all and git log --oneline main..upstream/main before you integrate. That is the same fetch-then-inspect habit you used with two local clones.

Sync by integrating, then pushing origin

git switch main
git fetch upstream
git log --oneline --decorate --graph --all
git merge upstream/main
git push origin main

Merge upstream/main into your local main when you intend to catch up. Then git push origin main publishes that catch-up on your fork. GitHub’s “Sync fork” button does a hosted version of the same idea; you should still be able to name the remotes and the Git commands.

If you already committed on main of the fork, integrating upstream can produce a merge commit or a conflict. Resolve it the way Git Merge Conflicts taught. Do not force-push main to make the graph pretty unless you are sure nobody else cloned that fork.

Do not push someone else's default branch

# This updates someone else's default branch if you have permission.
# You almost never want it, and GitHub usually rejects it.
git push upstream main

Maintainers publish on upstream. Your write path is origin, usually a feature branch, and later a pull request. Permission denied on git push upstream main is GitHub protecting the original default branch—not a broken SSH key. Do not force-push to “fix” it.

Guided practice: two remotes on one clone

1. 01
   Fork a public repository you do not own

   Use gh repo fork or the Fork button. Confirm the GitHub URL contains your username.

2. 02
   Clone your fork

   If the CLI did not clone, git clone the fork URL. Print git remote -v.

3. 03
   Add upstream if missing

   git remote add upstream pointing at the original. Fetch it.

4. 04
   Compare tips

   git log --oneline main..upstream/main. Integrate only if you mean to catch up, then git push origin main.

5. 05
   Refuse the wrong push

   Do not run git push upstream main. Write one sentence naming which remote you are allowed to update.

Independent lab: fork report

1. Fork a public GitHub repository you do not own. Clone your fork, not the original URL as origin.
2. Show git remote -v with origin pointing at your namespace and upstream pointing at the original.
3. Run git fetch upstream and record whether upstream/main matches your local main.
4. If you are behind, merge upstream/main and git push origin main. Do not push to upstream.
5. Write four lines: original URL, fork URL, the fetch command, and which remote you will never force-push.

Common fork mistakes

Lesson review

You can fork on GitHub, clone your copy, keep origin and upstream straight, and sync without overwriting someone else's default branch. The next lesson tracks work with GitHub Issues.

• I know a fork is a GitHub-hosted copy, not git clone.
• I can show origin as my fork and upstream as the original with git remote -v.
• I can git fetch upstream, integrate, and git push origin main.
• I do not push or force-push the original project's default branch.