File Write Operations Failing with Permission Errors
Your application fails when trying to write files to disk, throwing EACCES, EPERM, or permission denied errors. File uploads, log writing, cache storage, or report generation all fail because the application process doesn't have write access to the target directories.
This commonly happens when Claude Code generates code that writes to absolute paths like /tmp, /var, or the project root directory, but the deployment environment (Docker container, cloud function, or restricted server) doesn't allow writes to those locations.
The code works perfectly in local development where you run as an admin user, but breaks immediately in production where the application runs as a restricted service account.
Error Messages You Might See
Common Causes
- Hardcoded absolute paths — Code writes to /tmp or /var/data which may be read-only in containerized environments
- Read-only filesystem in serverless — Cloud functions and some container runtimes have read-only root filesystems
- Docker container running as non-root — The application user inside the container doesn't own the target directory
- Missing directory creation — Code tries to write a file before creating its parent directory
- SELinux or AppArmor restrictions — Security modules blocking file writes even when Unix permissions allow them
How to Fix It
- Use os.tmpdir() or platform-agnostic paths — Replace hardcoded paths with Node's os.tmpdir() or Python's tempfile.gettempdir()
- Create directories before writing — Always call fs.mkdirSync(dir, {recursive: true}) or os.makedirs(dir, exist_ok=True) before file operations
- Use /tmp in serverless — In AWS Lambda or similar, /tmp is the only writable directory. Configure your app to use it
- Set correct Docker permissions — Add RUN chown -R appuser:appuser /app/data in your Dockerfile for writable directories
- Use object storage for production — Replace local file writes with S3, GCS, or Supabase Storage for production deployments
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Get HelpFrequently Asked Questions
Why does file writing work locally but not in production?
Local development typically runs as your user with full permissions. Production environments (Docker, serverless, cloud VMs) run as restricted users with limited filesystem access. Always use platform-appropriate writable directories.
Where can I write files in AWS Lambda?
Only the /tmp directory is writable in Lambda, with a 512MB limit (configurable up to 10GB). For persistent storage, upload to S3 instead of writing locally.