`pre-commit` hangs on Windows with `parallel: true`

[CuriousStork]

Description

When parallel: true is set, pre-commit hangs:

• The hanged job output is interrupted. Please note, that the hanged job varies from run to run. For me sometimes it was Vale, sometimes Prettier.

• CTRL + C doesn't help.

• The terminal processes consume CPU continuously:

  

  Only killing via the task manager helps.

Sometimes all jobs seem to pass (or the terminal isn't stuck), but the output isn't full. For example, some jobs and Lefthook summary are missing. Maybe it's another issue, like #1047

Windows 10, Windows Terminal: 1.23.13503.0, PowerShell: 7.5.4.

The issue isn't reproduced when parallel is disabled.

.lefthook.yaml

assert_lefthook_installed: true
min_version: 2.0.12

pre-commit:
  parallel: true
  jobs:
    - name: "🔍Lint:"
      group:
        jobs:
          - name: markdownlint
            run: npx markdownlint-cli2 "{staged_files}" 2>&1
            glob:
              - "*.md"
          - name: Prettier
            run: npx prettier --list-different "{staged_files}"
            glob:
              - "*.md"
    - name: "💄Style:"
      group:
        jobs:
          - name: Vale
            run: vale --output=line "{staged_files}"
            glob:
              - "*.md"

Commands to reproduce

npx lefthook run pre-commit

Lefthook version

2.0.12

[mrexox]

Thank you for creating this issue. I will take a look as soon I am able to. But more likely next month

[danciudev]

Similar problem, in my case Windows 11, when running lefthook run pre-commit directly in the bash terminal of vscode, it freezes.

pnpm lefthook run pre-commit

My config with pnpm lefthook dump

lefthook.yml

assert_lefthook_installed: true
colors: true
commit-msg:
  parallel: true
  commands:
    commitlint:
      run: pnpm commitlint --edit {1}
      fail_text: ❌ Commit message does not meet the conventional commit format
    cspell:
      run: pnpm cspell --language-id commit-msg --no-progress --no-summary --show-suggestions {1}
      fail_text: ❌ Commit message contains spelling errors
extends:
  - apps/*/lefthook.yml
  - packages/*/lefthook.yml
min_version: 2.0.13
post-merge:
  parallel: true
  files: git diff-tree -r --name-only --no-commit-id ORIG_HEAD HEAD
  skip:
    - rebase
  commands:
    install-dependencies:
      run: pnpm install
      glob:
        - '{pnpm-lock.yaml,package.json}'
pre-commit:
  parallel: true
  jobs:
    - name: Monorepo
      group:
        parallel: true
        jobs:
          - name: Validate protected branch
            run: node scripts/validate-protected-branch.ts
            fail_text: ❌ Direct commits to protected branches (master/main) are not allowed
          - name: Validate branch name
            run: node scripts/validate-branch-name.ts
            fail_text: ❌ Branch name does not follow naming conventions
          - name: Validate pnpm lockfile
            run: pnpm install --frozen-lockfile --ignore-scripts
            fail_text: ❌ package.json does not correspond to pnpm-lock.yaml
          - name: cspell
            run: pnpm cspell --no-progress --show-suggestions {staged_files}
            fail_text: ❌ Staged files contain spelling errors
            glob:
              - '*.{jsx,tsx,md}'
          - name: secretlint
            run: pnpm secretlint --no-color {staged_files}
            fail_text: ❌ Staged files contain secrets
            glob:
              - '*'
    - name: redslim-os
      root: apps/redslim-os
      group:
        parallel: true
        jobs:
          - name: check-types
            run: pnpm check-types
            fail_text: ❌ TypeScript type checking failed
            glob:
              - '*.{ts,tsx}'
          - name: check-linter
            run: pnpm eslint --concurrency=auto --max-warnings=5 --no-warn-ignored --cache --cache-location ./.cache/eslint/ {staged_files}
            fail_text: ❌ Staged files did not pass linting
            glob:
              - '*.{ts,tsx,js,mjs,cjs,jsx,md,json,jsonc,json5,yaml,yml}'
          - name: check-format
            run: pnpm prettier --check --ignore-unknown --cache --cache-location ./.cache/prettier/ {staged_files}
            fail_text: ❌ Staged files are not properly formatted
            glob:
              - '*'

[guillempuche]

Confirming this also reproduces on Linux Ubuntu lefthook v1.12.2.

Setup: Yarn monorepo with 6 pre-commit commands running via parallel: true. Three of them use stage_fixed: true (Biome linter, syncpack formatter, dependency checker), and one runs Turborepo's check-types across affected workspaces.

Symptoms: Intermittent hang during git commit. The hung command varied between runs. Required Ctrl+C or kill to recover. Exactly matches the behavior described in this issue.

Likely cause: The combination of parallel: true + stage_fixed: true creates a race on the git index — multiple hooks reading/writing staged files concurrently.

Workaround: Setting parallel: false at the pre-commit level. Sequential execution adds ~5-10s but completely eliminates the hang. Validated with:

• Multi-file commits across 5+ packages (Turborepo fan-out, not all cached)
• Biome auto-fix with stage_fixed re-staging corrected files
• 3 consecutive commits with zero hangs

Config: lefthook v1.12.2, Linux 6.x, Yarn 4 + Turborepo 2.x + Biome 2.x.

---

Update (2026-02-16): The parallel: false workaround does not fully resolve the issue. We're now seeing hangs on lefthook v1.13.6 with parallel: false as well.

New findings:

• The yarn child process spawned by lefthook enters zombie state (Z) — it has exited but lefthook never reaps it, causing the entire hook to hang indefinitely.
• Observed via cat /proc/<pid>/status showing State: Z (zombie) on the yarn process, while lefthook itself remains alive waiting.
• Ctrl+C does not work; requires kill <lefthook_pid> to recover.
• This suggests the root cause is not purely a parallel + stage_fixed race, but a deeper process management issue in lefthook's child process handling (likely missing or blocked Wait() call on the spawned shell).

Config: lefthook v1.13.6, Linux 6.17, Yarn 4 + Turborepo 2.x + Biome 2.x.

[mjlehrke]

Had this happen as I was attempting to set up a monorepo with pnpm and lefthook. Very minimal monorepo reproduction attached:
lefthook-pre-commit-bug.zip

1. run git init to start a repo
2. run pnpm install to install monorepo packages (just eslint for the reproduction here)
3. run git add . to add files to git
4. run pnpx lefthook run pre-commit to crash the terminal

---

I'm running:

• latest lefthook
• latest pnpm
• latest eslint
• node V25.2.1
• Windows 11

Crash happens both within vscode or just running from the command prompt. As mentioned by others, it happens when parallel: true is set under pre-commit commands. Does not seem to matter if stage_fixed: true is present, crashes even without.

Each time it crashes, a node.exe process, lefthook.exe, and command prompt process are left running.