private-fork-sync

name	private-fork-sync
description	Make a public GitHub fork private and keep it synced with its upstream parent. Use when the user wants to make a fork private, or to pull/sync newer commits from the upstream parent into their fork.

Convert a fork's visibility to private, then keep it current by fetching from the parent. The whole workflow stays effortless on one condition: the fork's default branch is a clean mirror of upstream, so every sync is a fast-forward — no merge commits, no conflicts.

Prerequisite: gh authenticated with repo scope, plus a local clone of the fork. Examples use master; if the repo's default branch is main, substitute it (gh repo view <owner>/<fork> --json defaultBranchRef -q .defaultBranchRef.name).

Make a fork private

GitHub now converts a fork's visibility in place — historically this was blocked, which is why mirror-clone workarounds still circulate; you don't need them.

gh repo edit <owner>/<fork> --visibility private --accept-visibility-change-consequences

--accept-visibility-change-consequences is required, and the command prints nothing on success.

Completion: gh repo view <owner>/<fork> --json visibility,isPrivate reports PRIVATE / true.

Tell the user two consequences:

• While private, you can't open PRs from the fork to the public parent. Reverse with --visibility public --accept-visibility-change-consequences when you want to contribute upstream.
• Anyone who could see the public fork now needs to be added as a collaborator.

If the direct change is ever rejected (e.g. org policy), fall back to the documented mirror method: create a new private repo, then git clone --bare the fork and git push --mirror into it.

Set up syncing (one-time)

Add the parent as a fetch-only upstream remote, with push disabled so you can never accidentally push to a repo you don't own:

git remote add upstream https://github.com/<parent-owner>/<repo>.git
git remote set-url --push upstream DISABLE
git fetch upstream

Completion: git remote -v shows upstream fetch plus push URL DISABLE.

Sync when upstream has new commits

git fetch upstream
git checkout master
git merge upstream/master
git push origin master

One-liner alternative (relies on the same clean mirror condition): gh repo sync <owner>/<fork> -b master then git pull origin master.

Completion: git rev-list --left-right --count master...upstream/master prints 0 0 (local neither ahead nor behind).

Keep the mirror clean

The fast-forward guarantee holds only while master carries no commits of your own. Custom work goes on a separate branch, never on the mirror branch:

git switch -c my-changes        # do your work here, not on master
git switch my-changes && git rebase master   # pick up upstream after each sync

If master has already diverged, git rev-list above shows a nonzero left count and the merge stops fast-forwarding — move those commits onto a branch and hard-reset master to upstream/master to restore the mirror.