# GitHub Actions "fatal: detached HEAD" after actions/checkout

> Fix GitHub Actions git operations failing because actions/checkout leaves the repo on a detached HEAD at a specific commit, not on a branch.

Source: https://latchkey.dev/learn/github-actions/gha-checkout-detached-head-default  
Updated: 2026-06-26

By default actions/checkout checks out the exact commit that triggered the run, leaving HEAD detached. Commands that assume a current branch (push to HEAD, git symbolic-ref) then fail.

## Diagnose it: print the context before you change anything

Most workflow-expression bugs are not syntax errors, they are an expression reading something that is empty. GitHub resolves a missing property to an empty string instead of failing the run, so a wrong reference looks like a logic bug rather than a mistake. Dump the contexts first and you will usually see the answer immediately.

```.github/workflows/ci.yml
- name: Dump contexts
  run: |
    echo '--- github ---'   ; echo '${{ toJSON(github) }}'
    echo '--- needs ---'    ; echo '${{ toJSON(needs) }}'
    echo '--- steps ---'    ; echo '${{ toJSON(steps) }}'
    echo '--- matrix ---'   ; echo '${{ toJSON(matrix) }}'
    echo '--- inputs ---'   ; echo '${{ toJSON(inputs) }}'
```

> An empty `{}` or a blank line is the finding. It means the context is not populated at that point, which is a different problem from the value being wrong, and it needs a different fix.

## Check the context is allowed where you used it

Contexts are not available everywhere. The same expression can be valid in a step `if` and invalid in a job `if`, which is why an expression that works in one workflow fails when moved.

| Where you wrote it | Contexts available there |
| --- | --- |
| `run-name` | `github`, `inputs`, `vars` |
| `concurrency` | `github`, `inputs`, `vars` |
| Top-level `env` | `github`, `secrets`, `inputs`, `vars` |
| `jobs.<id>.if` | `github`, `needs`, `vars`, `inputs` |
| `jobs.<id>.steps.if` | `github`, `needs`, `strategy`, `matrix`, `job`, `runner`, `env`, `vars`, `steps`, `inputs` |
| `jobs.<id>.outputs` | Full access, including `secrets` |
| Reusable workflow `outputs` | `github`, `jobs`, `vars`, `inputs` |

> The most common trap in this table: `steps` and `matrix` are available in a **step** `if` but not in a **job** `if`. Moving a condition up a level silently breaks it.

## Catch it before it reaches CI

Every failure in this cluster is statically detectable. `actionlint` parses workflow expressions, checks context availability against the same rules above, and validates `needs` references, so these bugs never need to cost you a run.

```Terminal
# one-off
docker run --rm -v "$(pwd):/repo" --workdir /repo rhysd/actionlint:latest -color

# as a job, before anything expensive runs
- uses: actions/checkout@v4
- run: |
    bash <(curl -s https://raw.githubusercontent.com/rhysd/actionlint/main/scripts/download-actionlint.bash)
    ./actionlint -color
```

## FAQ

### What causes GitHub Actions "fatal: detached HEAD" after actions/checkout?

There are 2 common causes: default checkout detaches head and pushing without naming a branch. checkout fetches and checks out the triggering SHA directly, so HEAD points at a commit rather than a branch ref.

### How do I fix GitHub Actions "fatal: detached HEAD" after actions/checkout?

Check out a branch or push to an explicit ref. Pass ref: with the branch name to checkout, or check it out after.

### What does GitHub Actions "fatal: detached HEAD" after actions/checkout actually mean?

A step that tries to commit/push or read the current branch fails because the repo is in detached-HEAD state, with "fatal: detached HEAD" or a push that has no upstream branch.

### How do I stop GitHub Actions "fatal: detached HEAD" after actions/checkout happening again?

Decide explicitly whether you need a branch checkout vs a SHA. The prevention section lists 3 changes that keep it from recurring.

---

Latchkey runs CI/CD that repairs its own failures. Agent entry points: https://latchkey.dev/agent.txt, https://latchkey.dev/openapi.json, https://latchkey.dev/llms.txt