Flutter Pub Get Stuck

Flutter CLI Stuck / Hangs / Invalid SDK Hash — Diagnosis & Fix

When to Use

Use this skill when:

• flutter pub get, flutter build, flutter run, or ANY Flutter CLI command hangs indefinitely (no output for > 30 seconds)
• You see Can't load Kernel binary: Invalid SDK hash error
• fvm flutter commands produce zero output
• Flutter commands were working before but suddenly stopped

Root Cause Checklist

Work through these in order — each step resolves a progressively deeper issue.

1. 🧟 Zombie dart.exe / java.exe Processes (Most Common)

Symptoms: Flutter command shows no output, or hangs at "Resolving dependencies..."

Diagnosis:

Get-Process -Name dart,flutter,java -ErrorAction SilentlyContinue | Format-Table Name,Id,CPU,WS -AutoSize

Key Indicators:

• More than 5 dart.exe processes → likely zombies
• Any dart.exe using > 200MB memory (WS column) → stuck analysis/compilation
• java.exe running > 500MB → Gradle daemon holding resources
• A flutter run running for hours in another terminal → WILL block everything
• IDE analysis server constantly respawning dart.exe → kill IDE too

Fix:

# Kill all Flutter-related processes
Get-Process dart,java,flutter -ea 0 | Stop-Process -Force -ea 0
Start-Sleep 2
# Verify zero remaining
Get-Process dart,java -ea 0 | Measure-Object | Select-Object -ExpandProperty Count

[!WARNING] The IDE (VS Code / Android Studio) analysis server will respawn dart.exe processes. If zombies keep coming back, close the IDE first.

2. 🔒 Flutter SDK Lockfile

Symptoms: Zero output from any Flutter command. Zombie processes already killed but still hangs.

Diagnosis & Fix:

For FVM projects, first find the SDK path:

# Read .fvmrc to find the Flutter version
Get-Content .fvmrc
# Common FVM paths on Windows:
#   C:\Users\<USER>\fvm\versions\<version>\
#   C:\Users\<USER>\AppData\Local\fvm\versions\<version>\

Then remove the lockfile:

$sdkCache = "C:\Users\$env:USERNAME\fvm\versions\<VERSION>\bin\cache"
Remove-Item "$sdkCache\lockfile" -Force -ErrorAction SilentlyContinue
Remove-Item "$sdkCache\flutter.bat.lock" -Force -ErrorAction SilentlyContinue
Remove-Item "$env:LOCALAPPDATA\Pub\Cache\lock" -Force -ErrorAction SilentlyContinue

3. 💀 Corrupted bin/cache — "Invalid SDK Hash" (Nuclear Option)

Symptoms:

• Can't load Kernel binary: Invalid SDK hash error
• Flutter commands hang even after killing processes and removing lockfiles
• dart.exe --version works but flutter --version hangs
• Deleting just the snapshot or lockfile doesn't help

Root Cause: The Dart SDK cached inside bin/cache/dart-sdk/ is mismatched with the Flutter SDK version, or the flutter_tools.snapshot is corrupted. This typically happens after:

• Interrupted flutter upgrade
• Multiple FVM version switches
• Disk space issues during SDK download
• System crashes during Flutter operations

Fix — Delete entire bin/cache:

# Step 1: Kill ALL dart/java processes
Get-Process dart,java,flutter -ea 0 | Stop-Process -Force -ea 0
Start-Sleep 2

# Step 2: Delete the entire bin/cache directory
$sdkPath = "C:\Users\$env:USERNAME\fvm\versions\<VERSION>"
cmd /c "rd /s /q $sdkPath\bin\cache"
# If rd fails on locked files, kill cmd.exe processes holding locks:
# Get-Process cmd -ea 0 | Stop-Process -Force -ea 0
# Then retry rd

# Step 3: Verify deletion
Test-Path "$sdkPath\bin\cache"  # Should return False

# Step 4: Reactivate FVM (fixes FVM's own snapshot mismatch)
& "$sdkPath\bin\cache\dart-sdk\bin\dart.exe" pub global deactivate fvm
& "$sdkPath\bin\cache\dart-sdk\bin\dart.exe" pub global activate fvm
# If dart.exe doesn't exist yet (cache deleted), use system dart:
# dart pub global deactivate fvm; dart pub global activate fvm

# Step 5: Run flutter doctor to trigger fresh SDK download
fvm flutter doctor -v
# This will:
#   - Download Dart SDK from Flutter engine
#   - Expand archive
#   - Build flutter_tools
#   - Run pub upgrade

[!IMPORTANT] Remove-Item -Recurse in PowerShell often silently fails on locked files. Always use cmd /c "rd /s /q <path>" for reliable recursive deletion, and verify with Test-Path afterward.

[!IMPORTANT] After deleting bin/cache, Flutter will re-download ~200MB of Dart SDK. Make sure you have internet connectivity. The first flutter doctor after cache deletion takes 2-5 minutes.

4. 📡 Network Issues (pub.dev unreachable)

Diagnosis:

ping pub.dev -n 3
Invoke-WebRequest -Uri "https://pub.dev" -UseBasicParsing -TimeoutSec 5

Fix:

# Use Chinese mirror if behind firewall
$env:PUB_HOSTED_URL = "https://pub.flutter-io.cn"
$env:FLUTTER_STORAGE_BASE_URL = "https://storage.flutter-io.cn"
flutter pub get

5. 🧹 Corrupted Pub Cache

Fix:

flutter clean
Remove-Item pubspec.lock -ErrorAction SilentlyContinue
flutter pub cache repair
flutter pub get

One-Liner Emergency Fix

# Kill everything → delete locks → clean → retry
Get-Process dart,java,flutter -ea 0 | Stop-Process -Force; Start-Sleep 2; Remove-Item pubspec.lock -ea 0; fvm flutter clean; fvm flutter pub get

Nuclear One-Liner (when Invalid SDK hash)

# Kill everything → nuke cache → reactivate FVM → rebuild
Get-Process dart,java -ea 0 | Stop-Process -Force; Start-Sleep 2; cmd /c "rd /s /q C:\Users\%USERNAME%\fvm\versions\<VERSION>\bin\cache"; dart pub global deactivate fvm; dart pub global activate fvm; fvm flutter doctor -v

Finding the FVM SDK Path

The FVM SDK path varies across machines. To find it programmatically:

# Method 1: Check where fvm.bat is located
where.exe fvm
# Usually: C:\Users\<USER>\AppData\Local\Pub\Cache\bin\fvm.bat

# Method 2: Look for flutter.bat in the user's fvm directory
Get-ChildItem "C:\Users\$env:USERNAME\fvm\versions" -Filter "flutter.bat" -Recurse -Depth 3 -ea 0 | Select-Object -First 5 -ExpandProperty FullName

# Method 3: Common locations
# C:\Users\<USER>\fvm\versions\<VERSION>\bin\flutter.bat
# C:\Users\<USER>\AppData\Local\fvm\versions\<VERSION>\bin\flutter.bat

Prevention

1. Always stop flutter run before running flutter pub get — a hot-reloading session locks Dart processes
2. Don't run multiple Flutter CLI commands simultaneously in different terminals
3. Close IDE before major cleanup operations — the analysis server respawns dart.exe
4. Check for zombie processes if your machine feels slow or after IDE crashes
5. Don't interrupt flutter upgrade — if you must, delete bin/cache afterward
6. When using FVM, stick to one version per terminal session — rapid version switching can corrupt the cache

Related skills

• systematic-debugging — use when flutter pub get hangs to diagnose whether it's a process lock, network issue, or corrupted cache.
• fvm-flutter-release — for release builds, ensure flutter pub get completes cleanly before using FVM for version-specific builds.