fatal: You are not currently on a branch.

[bidipeppercrap]

config

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v1
        with:
          node-version: 12
      - run: npm ci
      - name: Build CSS
        run: npm run build
      - name: Push to GitHub
        run: |
          git config user.name github-actions
          git config user.email github-actions@github.com
          git add .
          git commit -m "Build CSS"
          git push

log

Run git config user.name github-actions
  git config user.name github-actions
  git config user.email github-actions@github.com
  git add .
  git commit -m "Build CSS"
  git push
  shell: /bin/bash -e {0}
[detached HEAD 706b5f8] Build CSS
 2 files changed, 2 insertions(+), 2 deletions(-)
 rewrite dist/css/plane.min.css.map (83%)
fatal: You are not currently on a branch.
To push the history leading to the current (detached HEAD)
state now, use

    git push origin HEAD:<name-of-remote-branch>

##[error]Process completed with exit code 128.

tried (not working)

    fetch-depth: 0
    ref: ${{ github.event.pull_request.head.ref }}

    fetch-depth: 0
    ref: master

[domgreen]

I seem to get the same ... I am running on a self-hosted runner that generates files and would like to commit back to the repo but get exactly the same as above.

[sigute]

I had same issue running push command in pull request. I managed to dig down into this old issue. It seems like the problem is that pull requests are not the same as regular branches, and solution ended up being to add this configuration option to my script:

uses: actions/checkout@v2
with:
  ref: ${{ github.event.pull_request.head.ref }}

[ChrisAcrobat]

Two years later.
I just had this problem as well, but I'm not working with a pull request. This solved it for me:

uses: actions/checkout@v3
with:
  ref: ${{ github.ref_name }}

[cezar-tech]

3 years later I also had this problem

uses: actions/checkout@v3
with:
  ref: ${{ github.ref_name }}

solved it for me