A couple of months back, I had jailbroken and unlocked one of my iPhones. To prepare for WWDC 2012 starting next week, I decided to restore my iPhone to be in the good books of Apple and not having to carry around a jailbroken iPhone. However, when I tried to upgrade my iPhone to the latest version of iOS 5.1.1, I was greeted with error 21. Error 21 goes like this ” The iPhone could not be restored. An unknown error occurred (21).”
Go to Apple Support forum to look for a resolution of error 21 and you’d probably find one of the most generic and useless information out there. Have a look yourself here.
If you’re also facing error 21, in all likelyhood, the phone was either jailbroken or physically damaged. In the latter case, you can get a replacement from Apple. US$149 for a 3Gs or 4 (or 3G, but that wouldn’t be worth it at this point), US$199 for a 4S. If it was jailbroken, they won’t touch it. So, what do you do? Don’t worry, we’re here!
Some of the scenarios in which “An unknown error occurred (21)” shows up:
- Upgrading to a newer version of iOS on your iPhone
- Restoring your iPhone
There are 2 easy solutions to resolve error 21. Use either one, which best suits you. You will find plenty of solutions on the internet, do not try one which seems risky, else your iPhone will turn into a brick in no time!
How to Fix iPhone Restore Error 21 – Option # 1
Easiest option is to upgrade or restore using a computer, which you’ve not used before or belongs to someone else. Bottom line is that you need to use a computer (Mac or PC) other than the one, which gave you error 21. If you have only one computer, you will have to edit your host file (option # 2) because it has an entry, which is preventing upgrade or restore of your iPhone and resulting in error 21.
How to Fix iPhone Restore Error 21 – Option # 2
If you do not want or have another computer to resolve iTunes error 21, you can edit your host file.
Windows users - Navigate to C:WindowsSystem32driversetc and locate “hosts” file.
Mac users – Navigate to privateetc and open the hosts file.
Next, you want to back up the hosts file somewhere and delete everything under the 127.******* local host line and save it.
Restart your iTunes in case of Mac and restart your computer in case of a PC.
Try to upgrade or restore or do whatever you were doing with your iPhone, you should not have any problems because of iPhone upgrade error 21 having been resolved!
Word of caution again – do not try to fix this error using softwares available in the internet. Your iPhone might turn into a brick (stuck in recovery mode forever).
Did this solution resolve your error? Let us know in the comments below.