Syncing GitLab master to GitHub Upstream

This guide covers setting up a one-way backup mirror: pulling master from a GitLab repo (origin) and pushing it to a GitHub repo you own (upstream). Useful when your GitLab instance has occasional downtime and you want a redundant copy.

Prerequisites

• An empty GitHub repository created in advance (do not initialize it with a README, license, or .gitignore — it should be completely empty).
• SSH keys configured for both GitLab and GitHub, or HTTPS personal access tokens.
• A local clone of the GitLab repo, ideally not shallow (see Avoiding Shallow Clone Issues below).

1. Check Existing Remotes

git remote -v

2. Add Remotes

If origin (GitLab) isn't configured:

git remote add origin git@gitlab.example.com:group/project.git

If upstream (GitHub backup) isn't configured:

git remote add upstream git@github.com:yourname/yourrepo-backup.git

To fix an existing remote pointing to the wrong URL, use set-url instead of add:

git remote set-url origin git@gitlab.example.com:group/project.git
git remote set-url upstream git@github.com:yourname/yourrepo-backup.git

3. Pull the Latest master from GitLab

git checkout master
git pull origin master

4. Push master to GitHub

git push upstream master

First time pushing this branch and want it tracked:

git push -u upstream master

5. Keep It Updated

Repeat steps 3–4 periodically, or wrap them in a script / cron job:

git pull origin master
git push upstream master

Full Mirror (All Branches + Tags)

For a complete mirror rather than just master:

git push upstream --all
git push upstream --tags

Or a one-shot full mirror clone into a separate folder:

git clone --mirror git@gitlab.example.com:group/project.git
cd project.git
git push git@github.com:yourname/yourrepo-backup.git --mirror

Avoiding Shallow Clone Issues

A shallow clone (e.g. git clone --depth 1) only has partial history. Pushing a shallow clone to a fresh remote can fail with errors like:

remote: fatal: did not receive expected object <sha>
error: remote unpack failed: index-pack failed

Check if your clone is shallow:

git rev-parse --is-shallow-repository

Fix it (requires origin to be reachable):

git fetch --unshallow origin
git push upstream master

If origin is unreachable (e.g. GitLab is down) and you need an emergency snapshot right now, push an orphan commit instead — this sacrifices history but backs up your current files immediately:

git checkout --orphan backup-temp
git add -A
git commit -m "Backup snapshot (shallow clone, full history pending)"
git push upstream backup-temp:master --force

Once origin is reachable again, redo the proper unshallow fetch and push to restore full history on GitHub.

Troubleshooting Checklist

Symptom	Likely Cause	Fix
remote unpack failed: index-pack failed	Shallow clone missing history	git fetch --unshallow origin
Failed to connect to <gitlab-host>	GitLab instance down/unreachable	Wait and retry, or use orphan-commit snapshot
! [rejected] master -> master (non-fast-forward)	GitHub master has diverged commits	git fetch upstream && git merge upstream/master, or --force if intentional overwrite
Push works but objects seem missing	Local repo corruption	git fsck --full, re-clone from origin if errors found

Notes

• --force rewrites remote history — only use it when you're certain no one else depends on the existing GitHub history.
• If you don't have push access to the original upstream GitHub project (collaboration scenario, not backup), use a fork + pull request workflow instead of direct pushes.