Flutter FileSystemException No Space Left On Device

When Flutter exits with FileSystemException: writeFrom failed, OS Error: No space left on device, errno = 28, the failing file write is usually a symptom. Measure temp folders, .dart_tool, pub cache, Gradle, Android emulator state, Xcode, and simulator storage before deleting anything broad.

Before clearing broad cache folders, capture the disk buckets around the failing Flutter command:

df -h
du -sh .dart_tool build ~/.pub-cache ~/.gradle/caches /tmp 2>/dev/null || true
du -sh ~/Library/Developer/Xcode/DerivedData ~/Library/Developer/CoreSimulator 2>/dev/null || true

If the failure is in CI, also print disk usage before and after:
- flutter pub get
- flutter test / flutter build
- Gradle assemble
- emulator or simulator startup

Then clean the proven bucket:
- .dart_tool/build for project-local generated state
- /tmp/flutter_tools.* for stale Flutter temp dirs
- Gradle cache only when Gradle owns the growth
- Xcode DerivedData/CoreSimulator only for iOS/macOS builds

Common Buckets

• Project-local generated state: .dart_tool, build, and test artifacts can grow during repeated runs.
• Flutter temp: stale /tmp/flutter_tools.* directories can survive interrupted runs.
• Pub and Gradle caches: usually rebuildable, but measure first so you do not slow every later build for no gain.
• Android emulator state: images, snapshots, and app data can be large and may be needed for reproduction.
• Xcode and simulators: iOS/macOS Flutter builds also touch DerivedData, CoreSimulator, DeviceSupport, and Archives.

Safer Cleanup Order

1. Record df -h and the biggest Flutter-adjacent folders before cleanup.
2. Close running Flutter, Gradle, emulator, simulator, and IDE processes that may still be writing.
3. Delete project-local generated state only when you can rebuild it.
4. Remove stale Flutter temp folders rather than every file in /tmp.
5. Clean platform caches through their owning tools where possible.
6. For CI, split the build around peak disk steps and print disk telemetry after each one.