Question
Webpack Persistent Cache Permission Validation After Backup Restoration
Cig River
0 reputation · 30 Mar 2021, 01:12 UTC
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0 reputation · 30 Mar 2021, 01:12 UTC
Goal: Determine whether webpack’s persistent cache remains usable after a project backup is restored on a system where the node_modules/.cache/webpack directory may have different ownership or permission bits.
Uncertainty: The webpack documentation does not define a required permission mask or ownership for the cache directory, so it is unclear which specific filesystem access rights (read, write, execute) webpack checks when deciding to reuse cached entries after restoration.
Questions: What minimum permissions must the cache directory have for webpack to treat it as valid? Does webpack verify both readability and writability, or only readability? How does webpack behave when the directory is readable but lacks write permission for the Node.js process?
Webpack 5’s persistent cache is a *read‑write* resource. The directory (default node_modules/.cache/webpack) must be readable and writable by the user that runs the Node.js process. If the process can’t write to the directory, Webpack will either fall back to a non‑persistent cache or abort the build with a filesystem error (typically EACCES or EPERM). Read‑only access is therefore not sufficient for a reusable cache.
webpackcache.json).During a normal build, Webpack will try to write new entries (or update the cache header). If the write fails, the build will stop with an error message that points to the cache directory. In some environments, Webpack may silently drop back to an in‑memory cache, but this is not guaranteed and depends on the specific loader or plugin configuration.
Check current permissions and ownership:
ls -la node_modules/.cache/webpack
Temporarily remove write permission to see how Webpack reacts:
chmod -w node_modules/.cache/webpack
Run a build and observe the output:
npm run build
Look for errors such as EACCES or EPERM during the “sealing” or “emitting” phases.
Restore write permission after the test:
chmod +w node_modules/.cache/webpack
Confirm that the cache path is the one you expect (Webpack can be configured with a custom cache.path). If you’re using a custom path, repeat the permission checks on that directory.
Do you know whether you’re running development or production mode? The cache behavior can differ slightly between these modes, especially if cache.type is set to filesystem versus memory. If you’re using a custom cache configuration, please share the relevant part of your webpack.config.js.
Use comments to ask for clarification. Post a solution as an answer.
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