Fix #1: Backup Your iPhone First (If Possible)
If your iPhone still boots, go to Settings, iCloud, iCloud Backup, and tap "Back Up Now," or connect it to your computer and use iTunes or Finder to click "Back Up Now." Before attempting any fixes, try to backup your iPhone since error 100 recovery methods might erase your data.
Steps:
- 1. If your iPhone still boots and isn't stuck in recovery mode, go to Settings > [Your Name] > iCloud > iCloud Backup
- 2. Tap "Back Up Now" and wait for the backup to complete
- 3. If your iPhone is stuck in recovery mode, connect it to your computer
- 4. Open iTunes (Windows) or Finder (Mac)
- 5. If iTunes/Finder recognizes your iPhone, click "Back Up Now" immediately
- 6. Wait for the backup to complete before proceeding with other fixes
Important:
If your iPhone is completely unresponsive or iTunes doesn't recognize it, you might not be able to backup. In this case, proceed directly to DFU mode restore. Unfortunately, you may lose data if you don't have a recent iCloud backup.
Fix #2: Use DFU Mode to Restore Your iPhone
Connect your iPhone to your computer, open iTunes or Finder, then enter DFU mode (press Volume Up, press Volume Down, hold Side until black, then hold Volume Down for 5 seconds), and click "Restore iPhone" when detected. DFU (Device Firmware Update) mode is the deepest restore mode available.
Steps for iPhone 8 and Later:
- 1. Connect your iPhone to your computer with a Lightning cable
- 2. Open iTunes (Windows) or Finder (Mac)
- 3. Quickly press and release the Volume Up button
- 4. Quickly press and release the Volume Down button
- 5. Press and hold the Side button until the screen goes completely black
- 6. As soon as the screen goes black, press and hold the Volume Down button while still holding the Side button
- 7. After 5 seconds, release the Side button but keep holding Volume Down for another 10 seconds
- 8. If done correctly, the screen will stay completely black (no Apple logo)
- 9. iTunes or Finder will detect an iPhone in recovery mode
- 10. Click "Restore iPhone" and follow the prompts
Steps for iPhone 7/7 Plus:
- 1. Connect your iPhone to your computer
- 2. Press and hold both the Side button and Volume Down button for 8 seconds
- 3. After 8 seconds, release the Side button but keep holding Volume Down
- 4. Keep holding Volume Down until iTunes/Finder detects the device
- 5. Click "Restore iPhone"
Why This Works:
DFU mode bypasses the iOS bootloader and allows iTunes or Finder to install firmware directly. Error 100 often happens when the normal update process encounters corrupted files or communication errors. DFU mode creates a clean slate by restoring the firmware from scratch, eliminating whatever caused the error during the normal update process.
Fix #3: Try a Different Computer
Use a different computer (ideally switch between Mac and PC), install the latest iTunes or macOS version, use a different USB cable and port, disable antivirus temporarily, and repeat the DFU restore process. Error 100 can be caused by issues with iTunes, USB drivers, or security software on your computer.
Steps:
- 1. If the first DFU mode restore failed, try using a different computer
- 2. Ideally, switch between Mac and PC if possible (e.g., if you used Windows, try a Mac)
- 3. Make sure the other computer has the latest version of iTunes (Windows) or is running a recent macOS version (Finder)
- 4. Use a different USB cable if available (preferably an Apple-certified cable)
- 5. Try different USB ports (use USB 2.0 ports if USB 3.0 ports are causing issues)
- 6. Disable antivirus and firewall software temporarily during the restore
- 7. Repeat the DFU mode restore process on the new computer
Why This Works:
Error 100 is sometimes caused by USB driver conflicts, outdated iTunes versions, or security software interfering with the restore process. A different computer has different drivers, different software, and possibly different USB hardware. This eliminates computer-specific issues and increases the chances of a successful restore.
Fix #4: Ensure Adequate Storage and Battery
Go to Settings, General, iPhone Storage and free up at least 5-10GB by deleting apps or photos, then charge your iPhone to at least 50% battery before attempting the update. iOS updates require both sufficient free storage space and adequate battery charge.
Steps:
- 1. If your iPhone is still accessible, go to Settings > General > iPhone Storage
- 2. Check how much free space you have. iOS updates typically need 5-10GB free
- 3. Delete apps, photos, or videos to free up space if needed
- 4. Charge your iPhone to at least 50% battery before attempting the update
- 5. Better yet, keep it plugged in during the entire update process
- 6. If doing a restore, ensure your computer has enough free disk space (at least 20GB) to download the iOS firmware file
- 7. Clear space on your computer by deleting temporary files if needed
Why This Works:
iOS updates download to your iPhone's storage, extract files, and apply changes. If there isn't enough space, the update fails partway through, potentially causing error 100. Similarly, if battery runs out during an update, the process aborts, leaving the iPhone in an inconsistent state. Adequate storage and battery ensure the update can complete without interruption.
Fix #5: Check for Carrier Settings and Network Issues
Ensure your computer has a stable internet connection, switch from WiFi to Ethernet if possible, temporarily disable VPN, and check Apple's System Status page at apple.com/support/systemstatus to verify activation servers are online. Sometimes error 100 appears when the iPhone is trying to verify activation with Apple's servers during restore.
Steps:
- 1. Ensure your computer has a stable internet connection during the restore
- 2. If using WiFi, try switching to Ethernet for a more stable connection
- 3. Temporarily disable VPN software during the restore process
- 4. Check Apple's System Status page (apple.com/support/systemstatus) to ensure activation servers are online
- 5. If you recently changed carriers or SIM cards, try using the original SIM during restore
- 6. After successfully restoring, update carrier settings by going to Settings > General > About (if an update is available, you'll see a prompt)
Why This Works:
During restore, iTunes or Finder must communicate with Apple's activation servers to verify your iPhone and complete the process. If your internet connection is unstable, VPN is interfering, or Apple's servers are having issues, error 100 can occur. A stable direct connection increases the chances of successful verification and activation.
Common Mistakes to Avoid
Avoid these mistakes to prevent data loss and restore failures.
- ✗Don't disconnect during the restore: Let the restore process complete fully even if it seems stuck. Disconnecting can brick your iPhone.
- ✗Don't use cheap third-party cables: Non-certified Lightning cables can cause communication errors during restore. Use Apple cables or MFi-certified ones.
- ✗Don't skip the backup step: Even if you're in a hurry, try to backup first. You can't recover data after a DFU restore without a backup.
- ✗Don't update on low battery: Always charge to at least 50% before starting an iOS update to prevent interruptions.
How to Prevent This Problem
Follow these practices to avoid error 100 during future iOS updates.
- ✓Enable automatic iCloud backups: Go to Settings > [Your Name] > iCloud > iCloud Backup and turn on automatic backups.
- ✓Wait a few days after iOS releases: Let others install major updates first. Check forums for reported issues before updating.
- ✓Keep iTunes and macOS updated: Outdated software on your computer can cause restore errors.
- ✓Free up storage regularly: Keep at least 10GB free on your iPhone for smooth updates.