Pkg Debug

pkg Debugging & Troubleshooting

Diagnose and fix issues when packaging Node.js apps with @yao-pkg/pkg.

User's issue: $ARGUMENTS

Official docs: https://yao-pkg.github.io/pkg/

For the full pkg configuration schema, patches examples, dictionary format, and contributing guide, see reference.md.

Triage — Start here

Identify the failure stage:

Diagnostic tools

CLI flags

pkg --debug app.js -o dist/app      # Inject diagnostic prelude (build-time)
pkg . --sea                          # Enhanced SEA (stock Node.js, no bytecode)
pkg . --no-bytecode                  # Standard mode without V8 bytecode
pkg . --options max-old-space-size=4096  # Bake Node.js flags into binary

Runtime environment variables

These work inside the packaged binary, not at build time.

Standard diagnostic workflow

# 1. Build with diagnostic prelude
pkg --debug . -o dist/app

# 2. List everything in the VFS
DEBUG_PKG=1 ./dist/app

# 3. Search for a specific file
DEBUG_PKG=1 ./dist/app 2>&1 | grep "myfile.json"

# 4. Trace all fs calls at runtime
DEBUG_PKG=2 ./dist/app

# 5. SEA startup profiling (no --debug needed)
DEBUG_PKG_PERF=1 ./dist/app

Build failures

ERR_REQUIRE_ESM

ESM module loaded via require().

pkg app.js --options experimental-require-module

Not needed on Node >= 22.12.0 (flag is default). See: https://yao-pkg.github.io/pkg/guide/troubleshooting#error-err-require-esm

Multiple occurences of sentinel (SEA)

@yao-pkg/pkg is in the project's dependencies — the walker bundles it into the SEA archive and the sentinel string causes postject to fail.

Fix: move @yao-pkg/pkg to devDependencies, or upgrade to pkg >= 6.16.0.

Bytecode compilation fails for cross-arch

Node 22 V8 bytecode is architecture-specific.

# Option 1: Use SEA (no bytecode step)
pkg . --sea -t node22-linux-arm64

# Option 2: Skip bytecode
pkg . --no-bytecode --public-packages '*' --public -t node22-linux-arm64

# Option 3: Target Node 24 (regression fixed)
pkg . -t node24-linux-arm64

Runtime errors

Cannot find module XXX (child_process)

Child process re-enters the packaged binary. Unset PKG_EXECPATH:

spawn(process.execPath, [...], {
  env: { ...process.env, PKG_EXECPATH: '' }
});

See: https://yao-pkg.github.io/pkg/guide/troubleshooting#error-cannot-find-module-xxx-when-using-child-process

Cannot execute binary from snapshot

OS can't exec binaries from VFS. Extract to disk first:

if (process.pkg) {
  const { pipeline } = require('stream/promises');
  const file = fs.createWriteStream('ffmpeg');
  await pipeline(fs.createReadStream('/snapshot/path/ffmpeg'), file);
  fs.chmodSync('ffmpeg', 0o755);
}

.node native addons are auto-extracted. Other binaries must be extracted manually. See: https://yao-pkg.github.io/pkg/guide/troubleshooting#error-cannot-execute-binary-from-snapshot

ERR_INSPECTOR_NOT_AVAILABLE / internalModuleStat is not a function

NODE_OPTIONS leaking from IDE/shell. Clear them:

unset NODE_OPTIONS NODE_DEBUG NODE_EXTRA_CA_CERTS NODE_NO_WARNINGS
./app

See: https://yao-pkg.github.io/pkg/guide/troubleshooting#error-err-inspector-not-available

Missing assets or modules

Why files go missing

1. Dynamic require(variable) — walker can't statically resolve it
2. Non-JS assets (templates, JSON, images) — not followed by walker
3. path.join with variable — path.join(__dirname, var) not detected

Auto-detection rules

pkg auto-detects path.join(__dirname, 'literal.ext') only when:

• Exactly 2 arguments
• Second argument is a string literal (not a variable, not a template with expressions)

See: https://yao-pkg.github.io/pkg/guide/detecting-assets

Manual configuration (package.json)

{
  "pkg": {
    "scripts": ["build/**/*.js"],
    "assets": ["views/**/*", "templates/**/*.html", "config/*.json"]
  }
}

• scripts — JS files compiled to V8 bytecode (source stripped).
• assets — raw files embedded as-is, accessible under /snapshot/.

Verification

pkg --debug . -o dist/app
DEBUG_PKG=1 ./dist/app 2>&1 | grep "expected-file"

If the file is missing, add it to assets. If it's a JS file loaded dynamically, add to scripts.

Binary bloat

Diagnose

pkg --debug . -o dist/app
SIZE_LIMIT_PKG=500000 FOLDER_LIMIT_PKG=2000000 DEBUG_PKG=1 ./dist/app

Fix with ignore

{
  "pkg": {
    "ignore": [
      "**/*/node_modules/*/test/**",
      "**/*/node_modules/*/docs/**",
      "**/*/node_modules/*/.github/**"
    ]
  }
}

Note: ** and * do NOT match dotfiles — spell .github explicitly.

Consider SEA with bundler

Pre-bundle with esbuild/webpack, then pkg --sea bundle.js. This produces the smallest SEA binaries because only reachable code is included.

See: https://yao-pkg.github.io/pkg/guide/advanced-debug-vfs

Cross-compile issues

Node 22 Standard mode regression

Standard cross-compile is broken on Node 22:

• linux-arm64 → runtime crash Error: UNEXPECTED-20 (#181)
• win-x64 → silent exit code 4, no output (#87)

Workarounds: (any one)

1. pkg . --sea (Enhanced SEA — works out of the box)
2. pkg . --no-bytecode --public-packages '*' --public (skip bytecode)
3. Target Node 20 or Node 24 (regression is Node-22-specific)

Cross-platform SEA builds

SEA cross-compile works when host major == target major. When they differ, pkg must execute the downloaded target binary to generate the blob — this fails for cross-platform builds (Linux host can't run macOS binary).

Rule: match host Node major to target Node major. Use nvm use <major> before running pkg.

Native addon issues

Native .node files are auto-extracted to ~/.cache/pkg-native/<sha256>/.

Common problems

• linuxstatic target cannot load native addons — use linux target
• Arch mismatch — .node must be compiled for target arch
• Cache deleted — antivirus may clean cache dir. Set PKG_NATIVE_CACHE_PATH
• Missing .node file — add to assets: "node_modules/pkg/prebuilds/**/*.node"

See: https://yao-pkg.github.io/pkg/guide/native-addons

SEA-specific issues

Mode selection

DEBUG_PKG_PERF=1 output interpretation

[pkg:perf] manifest parse       14.0ms    ← JSON parsing overhead
[pkg:perf] archive load          1.2ms    ← Raw binary load
[pkg:perf] vfs mount + hooks     3.3ms    ← fs patching
[pkg:perf] module loading      730.1ms    ← require() chain

High module loading → too many files; consider pre-bundling with esbuild.

Worker threads in SEA

SEA auto-patches the Worker constructor for /snapshot/ paths. If a worker fails to find its module, verify with DEBUG_PKG=1 that the file is in the VFS.

See: https://yao-pkg.github.io/pkg/guide/sea-mode

Patches and dictionaries

When a dependency uses code patterns that don't work in packaged apps (e.g. require('inspector'), hardcoded paths, dynamic imports), use patches in your package.json pkg config. pkg also ships built-in dictionary/ entries for known packages that are applied automatically.

For the full patches format, real-world examples, monorepo path conventions, dictionary file structure, and contributing guide, see reference.md.

Quick checklist

When a user reports any pkg issue, run through this:

1. What mode? Standard or SEA? (--sea flag or pkg.sea: true)
2. What Node version? Host and target (node --version, target triple)
3. Build or runtime failure? Does pkg succeed? Does the binary run?
4. DEBUG_PKG=1 — is the expected file in the VFS?
5. NODE_OPTIONS clean? — printenv | grep NODE
6. Stale cache? — rm -rf ~/.pkg-cache && pkg ...
7. Patches needed? — check if the failing module uses inspector, dynamic imports, or hardcoded paths → see reference.md
8. Native addons? — verify .node files match target arch
9. Cross-compile? — Node 22 Standard mode is broken; use SEA or Node 24
10. Bug in pkg itself? — see contributing guide