Ruby rails build failure

TL;DR

Fix: Community-resolved: the failure comes from files in the build directory with restrictive permissions (e.g.

The error

nixpacks build fails with `Error: Writing app. Caused by: Permission denied (os error 13)` while copying app files, e.g. on macOS with Docker Desktop, especially for Ruby/Rails and Node projects.

Fix

1. Community-resolved: the failure comes from files in the build directory with restrictive permissions (e.g.

Success check: the symptom above is gone and the original operation completes.

When to use

• You hit this exact symptom in nixpacks.
• You want the verified fix without digging through the thread.

When not to use

• A different error in nixpacks, even a similar-looking one.
• General nixpacks setup or credential questions.

Compatibility

• Nixpacks (railwayapp/nixpacks)

Variant phrasings

• How to fix "ruby rails build failure" in nixpacks
• nixpacks: ruby rails build failure
• ruby rails build problem

Edge cases

• Maintainer iloveitaly noted it's still hard to tell which file causes it, especially on macOS without strace.

Source

• https://github.com/railwayapp/nixpacks/issues/700

In gh:railwayapp/nixpacks#700 (https://github.com/railwayapp/nixpacks/issues/700), the question was: nixpacks build fails with Error: Writing app. Caused by: Permission denied (os error 13) while copying app files, e.g. The verified resolution: Community-resolved: the failure comes from files in the build directory with restrictive permissions (e.g. .viminfo/.bash_history with 600, read-only files like pnpm's global cache links in node_modules, or Go devenv dirs with 444 perms).