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iPhone 4 Jailbreak 4.2.1

Posted by: msbodetti

Tagged in: Mac , jailbreak , iPhone4 , iPhone , greenpois0n , geohot , firmware , chronic dev team , Apple


So I got my iPhone 4 in December and I was relieved to see the firmware on 4.1 because that time there was no untethered jailbreak for the 4.2.1 firmware until 2 weeks ago.
Reasons why I want to jailbreak my iDevice

  • Add 3rd party apps that iTunes doesn't have


  • Tweak the interface such as changing the name of the carrier (Which sounds stupid at first but I really like it when it reads my own title)


  • Download vwallpaper and have a moving background on home screen - You can even add a moving ringtone with this app which is tops


  • Another reason is to add cracked apps which is illegal but people still do it. What this means is that people who know their way around iTunes apps for iDevices, make them available for free to download than paying the fee on iTunes

There are a lot of other reasons but the above is the most often used for jailbreaking the iDevice. BTW it doesn't slow down the device, your device only slows down when you are running out of memory; like any other device.

How to do it?

  • First you need to update your iPhone 4 to the latest firmware which is 4.2.1. (I say iPhone because I used the jailbreak for iPhone 4 but apparently it is available for all iPhones, iPod touches and iPad)


  • Download the greenpois0n app from It is available for Windows, Mac and Linux. I used this on Mac.


  • Close all other apps and start the greenpois0n app you downloaded. A pop up will come to ask if you are jailbreaking the AppleTV. Just say no if your not.


Mac greenpois0n

  • The greenpois0n userface is really easy to navigate. You need to have your iPhone plugged in and ready with the 4.2.1 firmware and press the Jailbreak button on the bottom left and then instructions will highlighted above the button to put the device into DFU mode


  • Follow the instructions, if you did it wrong, it will say Failed. Maybe you put it into Recovery mode instead. Just switch the device back on by holding the sleep button.


  • If you did it right, the Jailbreak button will say Jailbreaking… Your iPhone will have a bunch of commands running down the screen and you then know that it is jailbreaking.


  • After that greenpois0n's Jailbreaking… Will say Finished or Complete. And now you must just wait for the device to boot back up again. You can unplug it now if you want, but if your battery is low,  keep it in.


  • The next thing you will see is the Apple boot logo morphing into the greenpois0n logo which is really sick.


  • You can then install Cydia by going to the Loader app that will be there after the Jailbreak. And install 3rd party apps, tweaks or utilities from there. Not all apps on there are free btw.

Problems I encountered

  • I didn't close all other apps and the greenpois0n app crashed and it kept on saying Jailbreaking… and Failed. I closed all apps and just opened greenpois0n only and it worked!


  • Cydia app didn't show on first download, rebooted the iPhone. Downloaded it again and it rebooted on its own and Cydia was there.

Big thanks to the Chronic Dev Team and many other contributors for making this jailbreak possible.


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