What is iTunes (iPhone) error 21

iTunes error 21 typically appears when you are trying to restore or update an iPhone through iTunes, and the process is interrupted. This error can be caused by a variety of issues, including problems with your hardware, software conflicts, or outdated software. In this article, we will explore what Error 21 is, why it appears, and provide a step-by-step guide to resolving the issue. Error 21 is categorized under the umbrella of iTunes error codes that relate to software update and restoration problems. This specific error often arises during the firmware update or restore process, primarily due to:

  • Hardware issues: Problems with USB ports or faulty cables.
  • Security software interference: Firewalls or antivirus programs that block the connection between iTunes and Apple servers.
  • Corrupt or outdated iTunes software: Outdated versions of iTunes may not support newer firmware or may contain bugs.
  • Jailbroken devices: Modifications to the iPhone’s operating system can interfere with the restore process.
  • Host file conflicts: Modifications in the host file can prevent iTunes from communicating with Apple’s update servers.

Download repair tool

Sometimes resolving the errors is out of our control and possibilities. This is where third-party tools are more than welcome to contribute and carry all the difficulties away. If you are facing error 21 or similar issues, but fail to benefit from any of the manual steps below, try using Tenorshare ReiBoot — a great recovery tool designed for resolving errors like that. Get to know how one can use it to address the errors and restore or update an iOS device successfully on their website.

Download iOS Repair Tool
  1. Download and install ReiBoot for either Mac or Windows.
  2. Once done, open the app and plug your device into the computer.
  3. The program should recognize your device and offer a couple of options.
  4. Choose Standard if you simply want to update your device, or Deep repair if you want to fully restore it.
  5. Then, download the firmware found by the app for your smartphone by clicking Download.
  6. Once the process is finished, click Repair now to start resolving the problems.
  7. Standard is meant to search for basic issues and bugs to address them without wiping out your data.
    Deep repair will reset your device to factory settings and delete the entire data stored on it.

  8. Wait until the app finishes its repair and restores your device. It will take about 15 minutes to end.

Step-by-Step Guide to Fix iTunes Error 21

Step 1: Update iTunes and Computer Software

Ensure that the latest version of iTunes is installed on your computer.

For Apple users:

  1. Open the App Store on your Mac.
  2. Click on the Updates tab.
  3. If an iTunes update is available, click Install.

For Windows users:

  1. Open iTunes.
  2. From the menu bar, select Help > Check for Updates.
  3. Follow the prompts to install any available updates.
  4. Also, make sure that your computer’s operating system is up-to-date.

Step 2: Check Your Hardware

  1. USB Cable and Port: Try using a different USB cable and switch to a different USB port on your computer. Avoid using USB hubs.
  2. Connect directly to your computer: Ensure that the connection is direct and not through any docks or intermediaries.

Step 3: Disable Security Software Temporarily

  1. Temporarily disable any firewall or antivirus software that could be blocking iTunes from accessing Apple’s servers.
  2. Attempt to update or restore your iPhone again.

Step 4: Check the Hosts File (Especially for Windows Users)

  1. Navigate to C:\Windows\System32\drivers\etc\ and find the hosts file.
  2. Open the file with Notepad as an administrator.
  3. Look for any lines containing apple.com and delete them or comment them out by adding # at the beginning of the line.
  4. Save the file and restart your computer.

Step 5: Put Your iPhone in DFU Mode

  1. Connect your iPhone to your computer and open iTunes.
  2. Press and hold the Home button and the Sleep/Wake button at the same time.
  3. After 8 seconds, release the Sleep/Wake button but keep holding the Home button until iTunes says, iTunes has detected an iPhone in recovery mode.
  4. Let go of the Home button. Your iPhone screen should be completely black.
  5. Try restoring your iPhone using iTunes.

Step 6: Use Another Computer

If all else fails, try to restore or update your iPhone using a different computer. This can help determine if the issue is related to your computer or the iPhone itself.


Fixing iTunes Error 21 involves a mix of checking hardware connections, updating software, adjusting security settings, and examining system files. By following these steps methodically, you can overcome this issue and restore or update your iPhone successfully. Always ensure that you back up your data before attempting any fixes to avoid data loss.

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James Kramer
Hello, I'm James. My website Bugsfighter.com, a culmination of a decade's journey in the realms of computer troubleshooting, software testing, and development. My mission here is to offer you comprehensive, yet user-friendly guides across a spectrum of topics in this niche. Should you encounter any challenges with the software or the methodologies I endorse, please know that I am readily accessible for assistance. For any inquiries or further communication, feel free to reach out through the 'Contacts' page. Your journey towards seamless computing starts here