iCloud Drive Not Syncing

When iCloud Drive stops syncing, files placed in your local iCloud Drive directory remain with stuck cloud upload status icons, or fails to populate in Finder/File Explorer. Unlike other platforms, iCloud is deeply integrated into the operating system kernel on macOS, meaning sync hangs often require resetting system daemon processes.

This technical guide walks you through restarting the background sync engines, clearing cached SQLite sync databases, and resetting local clients on both macOS and Windows.

1. Primary Causes of iCloud Sync Failures

iCloud synchronization stalls are usually caused by OS-level service hangs:

• Bird Daemon Freeze: The macOS background process responsible for iCloud Drive file transfers (bird) enters a hung state, freezing the queue.
• CloudDocs Cache Corruption: The SQLite database tracking local files in CloudDocs becomes desynchronized from iCloud servers.
• Apple ID Authentication Stalls: Expired security tokens block access until a manual two-factor re-verification is completed.
• iCloud for Windows Driver Crash: The Windows virtual filesystem filter driver fails to mount or communicate with iCloudDrive.exe.

A. Force Restart the Sync Daemon

If files are stuck in “Uploading” or “Waiting to sync”:

1. Open Terminal (via Spotlight search).
2. Run the command to kill the sync daemon. macOS will automatically relaunch a fresh instance:

   killall bird

B. Reset the CloudDocs Cache Database

If a simple process restart does not free up the queue, purge the local index database:

1. Close all documents and apps syncing with iCloud.
2. In Terminal, navigate to your Application Support directory:

   cd ~/Library/Application\ Support

3. Delete the CloudDocs directory (this forces macOS to rebuild the index of your iCloud files without deleting actual data):

   rm -rf CloudDocs

4. Restart your Mac. Finder will display progress bars as it re-downloads and re-indexes your iCloud Drive folders.

A. Force Close iCloud Background Tasks

1. Right-click the Taskbar and open Task Manager.
2. Expand the processes list and locate any entries matching iCloud.
3. Select and end tasks for:
   • iCloudDrive.exe
   • iCloudServices.exe
   • iCloudPhotos.exe
4. Or, run this command in Command Prompt (Admin):

   taskkill /f /im iCloudDrive.exe /im iCloudServices.exe /im iCloud.exe

B. Clear Temporary Cache and Restart

1. Press Windows Key + R to open the Run window.
2. Type or paste the following path and press Enter:

   %localappdata%\Packages\AppleInc.iCloud_sr379ee5v9y2t

   (Note: Path may vary if installed via standalone installer rather than Microsoft Store. Try %localappdata%\Apple Computer\iCloud instead).
3. Relaunch iCloud from the Start Menu.

4. Verify Account & Access Permisions

If the sync engine is healthy but sync is still failing, check account status:

• Check Storage Quotas: If your iCloud account is full, sync halts completely. Log in to iCloud Web Portal to verify your storage usage.
• Re-Authenticate Session: On Mac, open System Settings → click your Apple ID name. If there is a warning saying “Update Apple ID Settings”, enter your Apple ID password and complete two-factor authentication.
• Enable iCloud Drive Toggle: In System Settings, go to iCloud → iCloud Drive and verify that it is turned On and that applications like Desktop and Documents folders are checked if you want them synced.

5. Summary Diagnostics Checklist

• Kill bird Daemon (Mac): Run killall bird in Terminal to restart the sync engine.
• Reset CloudDocs (Mac): Delete the folder ~/Library/Application Support/CloudDocs to force a database index rebuild.
• Taskkill iCloud (Win): Force close iCloudDrive.exe via Task Manager or cmd.
• Update Apple ID Settings: Check System Settings to resolve credential authentication warnings.
• Verify iCloud Web Portal: Log in to icloud.com to verify file visibility and storage quota limits.