fix: Replace io.mv with copy+delete to fix EXDEV errors in DinD environments @jamengual (#106)
## SummaryThis PR fixes the EXDEV (cross-device link not permitted) error that occurs when using this action in Docker-in-Docker (DinD) and other containerized environments.
Fixes #98
Problem
In DinD environments (like ARC runners), the GitHub Actions temp directory (/__w/_temp/) and the installation target directory exist on different Docker filesystem layers. When the action attempts to use io.mv() (which calls fs.renameSync()), it fails with:
Error: EXDEV: cross-device link not permitted, rename '/__w/_temp/88be01d7-...' -> '/__w/_actions/cloudposse/github-action-setup-atmos/atmos/atmos'
This is a fundamental limitation of the rename system call - it cannot move files across different filesystems or device boundaries.
Solution
This PR implements two fixes:
1. Replace io.mv() with copy+delete pattern
File: src/installer.ts:218-223
- Before:
await io.mv(downloadPath, toolPath)- fails across device boundaries - After:
await io.cp(downloadPath, toolPath)+await io.rmRF(downloadPath)- works across all filesystems
This is the standard workaround for cross-device file operations and is used throughout the GitHub Actions ecosystem.
2. Add detection for pre-installed atmos
Files: src/installer.ts:45-75, src/installer.ts:243-268
Added checkExistingAtmosInstallation() function that:
- Checks if atmos is already available in PATH
- Retrieves the installed version
- Uses the existing installation if it satisfies the requested version spec
- Falls back to downloading if version doesn't match or not found
This benefits users who:
- Pre-install atmos in custom runner images
- Use the action in environments with atmos already available
- Want to reduce unnecessary downloads and installation time
Benefits
- ✅ Works reliably in DinD environments (ARC runners, containerized CI/CD)
- ✅ Reduces unnecessary downloads when atmos is pre-installed
- ✅ Maintains full backward compatibility
- ✅ Proper error handling with debug logging
- ✅ No breaking changes to the action interface
Testing Recommendations
- DinD Environment: Test in ARC DinD mode runner
- Pre-installed atmos: Test with atmos already in PATH
- Version matching: Test with version specs (latest, specific versions, semver ranges)
- Fallback behavior: Test when existing version doesn't satisfy requirement
- Standard runner: Verify it still works in standard GitHub-hosted runners
Technical Details
The io.mv() function from @actions/io uses the underlying ioUtil.rename() method, which relies on the OS-level rename syscall. This syscall has the limitation that it cannot move files across different filesystem mount points or devices.
In Docker-in-Docker:
- Temp directory:
/__w/_temp/(on one overlay filesystem) - Installation directory:
/__w/_actions/...(on a different overlay filesystem) - Result:
EXDEVerror when attempting rename
The copy+delete pattern avoids this limitation by performing two separate operations, each within their respective filesystems.
Related Issues
- Fixes #98
- Related discussion in cloudposse/github-action-atmos-terraform-plan about DinD compatibility
