Git detached HEAD first triage response

When this happens

Use this when only the visible message is known. Do not stop at the screen message; validate the first observable mismatch before any setting is changed first.

Symptom checklist

• detached HEAD appears repeatedly in the Git UI or logs.
• HEAD, upstream, rebase state, hooks, LFS differs between successful and failed requests.
• The issue appears only after separating local worktree issue from remote rejection.
• It often follows deploys, permission changes, configuration edits, or data refreshes.

Likely causes

• detached HEAD specifically changes the investigation surface for Git: verify the exact failing object, route, user, and timestamp before applying the broader pattern.
• Local history diverged from the remote branch.
• A rebase, merge, or submodule operation left the index in a partial state.
• Large files or line endings changed outside the repository policy.
• A tag or protected branch already exists on the remote.
• Authentication succeeds but remote policy rejects the update.
• For the first triage case, the first useful clue is the first observable mismatch before any setting is changed.

First 1-minute checks

1. Write down the first failure time, latest change, affected user, path, and object ID.
2. Compare HEAD, upstream, rebase state, hooks, LFS for success and failure in the same window.
3. Test the hypothesis: Git workflow failure caused by divergent history, unresolved index state, LFS/large files, line endings, submodules, tags, or remote policy.
4. Classify this as first triage: the first observable mismatch before any setting is changed.
5. Capture current values before changing configuration.

First evidence

Treat detached HEAD as a first triage case. First collect evidence for the first observable mismatch before any setting is changed.

Output examples

Normal output

No matching error appears during the affected request window.

Failing output

The same error appears at the exact request time with the affected path, user, or object.

Output-to-action branches

• Only the visible message is known.
  Collect timestamp, route, request ID, user, and the first backend log line before editing configuration.
• The working and failing outputs differ.
  Act on the differing layer first: For detached HEAD, apply the fix only after reproducing the same condition and saving the before/after evidence for this exact code.
• Command output is normal but users still fail.
  Separate browser cache, cookies, permissions, and network location before declaring it fixed.

Do not do this

• Do not change DNS, SSL, cache, and permissions at the same time.
• Do not change multiple layers before identifying the failing layer.
• Do not delete production data, grant broad permissions, or disable security controls as a first response.

Evidence quality

Auto-generated operator draft: includes issue-specific causes, commands, output branches, and unsafe-action warnings. Official-source links and real incident validation are queued for enrichment.

Commands to run first

grep -R "detached HEAD" ./logs

git status --short --branch

git log --oneline --decorate -5

git remote -v

git ls-files -s | head

git status --short --branch

git log --oneline --decorate -5

git ls-files -u

git remote -v

date -u && grep -R "ERROR\|WARN\|failed" ./logs | tail -n 50

Fix order

1. Record the full detached HEAD message, failing URL, user, object ID, and latest change.
2. Collect issue-specific evidence for Git workflow failure caused by divergent history, unresolved index state, LFS/large files, line endings, submodules, tags, or remote policy.
3. Compare the failing case with a successful case before editing settings.
4. If this is the first triage branch, Collect timestamp, route, request ID, user, and the first backend log line before editing configuration.
5. Re-check with the same command and URL, then record the normal output.

Actions by cause

• For detached HEAD, apply the fix only after reproducing the same condition and saving the before/after evidence for this exact code.
• Inspect branch, index, and remote state before editing files.
• Resolve conflicts once, then continue or abort the operation deliberately.
• Move large assets to LFS or remove them from history before pushing.
• Normalize line endings with repository attributes.
• Fetch tags and remote branch rules before retrying.
• For the first triage branch, Collect timestamp, route, request ID, user, and the first backend log line before editing configuration.

Evidence links

• Git documentation official
• GitHub authentication troubleshooting official

Verification metadata

• operator-draft
• official-reference-linked
• 2026-07-23

Update queue

• Review cadence
  weekly-source-review
• Next enrichment
  Add one official-source check and one real output example for Git detached HEAD.

Environment-specific checks

• Shared hosting, proxies, VPNs, or CDN layers can change local worktree issue from remote rejection results.
• Do not trust only the Git UI; compare command output.
• Japanese hosting panels may show completion before DNS or SSL fully propagates.
• Test from both office and external networks.

Prevent it next time

• Store normal examples for HEAD, upstream, rebase state, hooks, LFS.
• Add rebase/merge cleanup, upstream reset, LFS tracking, hook logs to the release checklist.
• Keep recurring errors in the same note format.
• Split alerts by error rate, latency, certificates, disk, and permission changes.

Related notes

• Git merge conflict first triage response
• Git non-fast-forward first triage response
• Git permission denied publickey first triage response
• Git large file first triage response
• Git rebase conflict first triage response
• Git submodule first triage response
• Git line endings first triage response
• Git tag exists first triage response