Git and GitHub / Editorial solution guide

Resolve a rejected non-fast-forward update

Inspect ancestry and preserve collaborators’ commits before choosing a merge or an agreed private-topic rebase.

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Recognize the symptoms

A proposed push is rejected as non-fast-forward, or a fast-forward-only local update refuses to proceed. The local and observed remote tips may both contain unique commits. Similar-looking rejection messages can also arise from branch protection or permissions, so read the actual reason rather than assuming every publication problem needs a history rewrite.

Understand the likely causes

  • A fast-forward requires the old destination tip to be an ancestor of the proposed new tip. Another contributor may have advanced the destination, or local history may have been rebased. A stale remote-tracking ref can hide that relationship. Authentication success does not imply ancestry safety or permission to update a protected branch.

Preserve work and identify the intended refs

Inspect status, current branch, upstream, and the intended destination. Save valuable uncommitted content and create an appropriate recovery reference before integration. Verify that the remote name and branch are the ones the project expects, without printing credentials. Do not retry with a force flag as a generic fix. If the rejection is a policy or authorization failure, follow that policy rather than changing ancestry. All practical commands in this guide belong to separately allocated local temporary repositories; no actual remote or push is used.

Refresh authorized knowledge and inspect divergence

Use the authorized fetch process to obtain current destination knowledge, then inspect unique commits and the graph before integrating. In validation, origin is a filesystem repository inside temporary storage, so no network is contacted. The read-only commands below assume that local lab fetch has already occurred. The first count is unique to main and the second to origin/main. Counts describe reachability, not lines or importance. Compare patches and confirm that no collaborator’s work is being dropped.

bash Inspect a local lab’s ancestry before integration 
git rev-list --left-right --count main...origin/main
git log --graph --oneline --left-right main...origin/main
git merge-base --is-ancestor origin/main main

The ancestry check exits 1 when origin/main is not an ancestor of main, even though the command itself ran normally. This is an expected diagnostic status for divergence, not a reason to discard the remote side.

Choose the agreed integration strategy

For shared work, a merge can preserve both existing histories. For a genuinely private topic, the project may permit replaying local commits on the updated base; preserve the old tip and understand that identities change. Resolve conflicts semantically and run relevant tests. The fragment below demonstrates the merge choice on a clean synthetic main branch. It is not a command to update a real shared branch. If a server requires pull requests, the reviewed result still follows that workflow rather than bypassing protection.

bash Preserve both histories in a temporary merge lab 
git branch safety/before-integration
git -c user.name="Lab Author" -c user.email="lab@example.invalid" merge --no-edit origin/main
git merge-base --is-ancestor origin/main HEAD

The final check exits 0 after successful integration. A conflict must be completed or deliberately aborted through the correct operation workflow. No push follows this example, and the course never publishes the result.

Verify the fix

Inspect the final graph and content, confirm the observed destination tip is reachable, and run the project’s relevant tests on the resulting candidate. Verify that both sides’ intended behavior remains. Another collaborator can advance the server later, so a successful local ancestry check is not a promise that a future push will be accepted. Publication requires a fresh authorized workflow and applicable server checks; no push is performed during this guide’s validation.

Keep it from recurring

  • Fetch and inspect before integration, keep coherent topics, coordinate shared-history changes, and use the repository’s pull-request policy. Treat force-with-lease as a narrowly scoped overwrite guard within an authorized rewrite, never as automatic permission to replace others’ work. Preserve recovery anchors until the result is reviewed and verified.

Official references