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How to Fix iTunes Error 21 When Restoring custom IPSW File?

Hello Jaxov, need help here. Few days back, I am trying to jailbreak my iPhone 4 on iOS 4.2.1 using Sn0wbreeze 2.5.1, but during the custom firmware restoration process, iTunes throws Error 21. This is a used iPhone 4 and it was jailbroken on iOS 4.3.1 using PwnageTool but the previous user said he did not encounter this error. What do I need to do to fix this error? My iPhone is dead. Please help, I’m a novice. Thanks in advance.

Asked by: Patrick from Jersey City, New Jersey

Hello Patrick, iTunes Error 21 occurs during the custom IPSW firmware using the recovery mode instead of the traditional DFU mode or Device Firmware Upgrade mode. So there’s a possibility that you may encounter Error 21 when you use PwnageTool or Sn0wbreeze jailbreak tools since these tools were used to create custom pre-jailbroken IPSW file, but chances to get error 21 is very low. By the way, are you planning to unlock your iPhone?  Why do you have to use Sn0wbreeze or PwnageTool to restore a custom firmware? If you don’t care about unlocking your iPhone from AT&T then you can just jailbreak your iPhone 4 using Redsn0w 0.9.6rc12 on iOS 4.2.1 or Redsn0w 0.9.6Rrc16 on iOS 4.3.3.

Anyway, to fix iTunes’ Error 21, you must put your iPhone (iPad or iPod Touch) into DFU mode. If you don’t know how to put your iOS device into DFU mode, then you can follow the step by step guide posted below:

Step 1: Connect your iPhone (iPad or iPod Touch) to your Mac or PC via USB cable (USB cable) and then launch iTunes.

Step 2: Then hold down the Home and Power button at the same time for 10 seconds.

Step 3: Release the Power button after 10 seconds but continue holding the Home button and wait for iTunes to detect your iPhone in recovery mode.

Step 4: Once your iPhone (iPad or iPod Touch) is in DFU mode, you should see nothing on its screen. It should be completely blank.

That’s it! You can now restore custom IPSW on your iPhone and hopefully this time you will not get iTunes Error 21.
How to fix iTunes Error 21

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    Simi8 years, 8 months ago

    Hi Javox! Im restoring my iPhone 4 to iOS 5.1.1. When im using Redsn0w versions 9.10, 9.11, 9.12 and 9.14 but it always gives me an error 21 even im in DFU mode not in recovery mode. But when I use sn0breeze 2.9.6 I can successfully restore my device to iOS 5.1.1. I just want to know why Redsn0w gives me error 21 in DFU mode but when using sn0wbreeze, it doesn’t give any errors. I used Redsn0w before and I can smoothly restore my device using it but when apple released the iOS 6 it already gives me that damn error. I want to get rid of it. I do appreciate your kindness.

    2shot8 years, 11 months ago

    i am also having the same problem… i followed the steps and it didnt stop where it was stopping the previous times but when the phone came on the error popped up again