How to Jailbreak iOS 4.2.1 GM on iPhone 4, 3GS, 3G, iPad and iPod touch with Redsn0w 0.9.6b2

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For these of you who don’t recognize, Redsn0w 0.9.6b2 is based on Geohot’s Limera1n exploit which can pwn all iOS devices for life.I have tested jailbreak of iOS 4.2.1 on my iPhone 4 and can confirm that it works. Though Cydia wont work just yet because Apple has changed some of the private APIs used by Cydia in 
iOS 4.2.x
 because of which Cydia crashes when you try to run.

The good news is that an iOS 4.2.1 compatible version of Cydia is ready and will go live as soon as iOS 4.2.1 is released to public. Also since you have full root access on the device, you can install jailbreak-apps via SSH for now until the new version of Cydia.

Cydia on iPhone 4, running iOS 4.2.1

Supported devices are:

NOTE: Those of you who rely on a carrier unlock MUST STAY AWAY from iOS 4.2.1.

Follow the step by step instructions posted below to jailbreak iOS 4.2.1 GM release with Redsn0w 0.9.6b2:

Redsnow

Step 1: Download iOS 4.2.1 GM & iOS 4.1 (required for Redsn0w 0.9.6b2) for your version of iOS device.

Step 2: Update/Restore to iOS 4.2.1 firmware using the IPSW file you just downloaded via iTunes 10.1.

Step 3: Start Redsn0w 0.9.6b2 and point it to iOS 4.1 (Final Version, NOT iOS 4.2.1) to proceed with the jailbreak.

Step 4: Now select “Install Cydia” and click “Next”. Optionally (if available), you can also select any other option you like.

Step 5: Now make sure your device is both OFF and PLUGGED IN to the computer before you click “Next”.

At this stage you will be presented with a screen where you will have to quickly hold “Power” button and then while holding the “Power” button, you will now have to hold “Home” button too. Now after few seconds release “Power” button but keep holding “Home” button until installation begins.

Step 6: Sit back and enjoy while redsn0w will do all the rest for you. Once done, your phone or iPod touch will restart automatically and you will find it jailbroken on the latest iOS 4.2.1firmware.

Download iOS 4.1 (Final version) for iPhone 4, 3GS, 3G, iPod touch
Download iOS 4.2.1 GM for iPhone 4, 3GS, 3G, iPad, iPod touch
Download Redsn0w 0.9.6b2 for Windows and Mac
Download iTunes 10.1 for Windows or Mac.

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