First things first: It’s always a good idea to backup your SHSB Blobs for the future, before you use any new jailbreak. For backing up your SHSH Blobs, please refer here.
Things you need to know before jailbreaking;
1) If you haven’t updated to iOS 4.2.1 you will need iTunes 10.1 to do it. You can download iTunes 10.1 here or you can update your iTunes via the apple software update.
iOS 4.2 is compatible with the iPhone 3G, 3GS, and iPhone 4, the iPod touch 2nd, 3rd and 4th generations, and the iPad.
2) Please keep in mind that the jailbreak is a tethered jailbreak. A tethered jailbreak means that each time your device loses battery power or needs to be rebooted, you must attach it to a PC or Mac to boot into the jailbroken state.
The best news of all is for owners of iPhone3G, older iPhone3GS, and non-MC iPod touch 2G. Due to a combination of our original pwnage2 exploit, the arm7_go exploit, 24kpwn, and limera1n, your device is “just as jailbreakable as ever.” You reap the full benefit of an untethered 4.2.1 jailbreak.
Next are the owners of all the more recent devices. The good news there is that due to geohot’s limera1n exploit, all recent devices can be jailbroken (this will be true until Apple released new hardware that fixes geohot’s limerain exploit in the bootrom). The bad news is that right now, the 4.2.1 jailbreak is *tethered* on all of these recent devices.
3. This jailbrak DOES NOT support the iPod touch MC versions.
So once you have the iOS 4.2.1 and backed up your SHSH Blobs, let’s get on with the jailbreaking process. (Upgrading to iOS 4.2.1 first isn’t really necessary, but it is recommended to do so)
1.) First download redsn0w version 0.9.6b4 from any of the following links:-
2.) Run Redsn0w.exe
Please note: If you’re using windows 7, you will have to use redsn0w in “XP Compatibility” mode.
3) click on browse and select the iOS 4.2.1 ipsw file. In windows 7 the file is located on:-
“C:UsersusernameAppdataroamingapple computeriTunesapple software updates”.
4) Once the ipsw file is identified, click Next.
5) Allow the kernel to be patched and click Next.
6) Select “Install Cydia” and press next.
7) Make sure your device is turned off.
8 ) Follow the onscreen instructions to put your iPhone into DFU mode.
A. Hold down the Power/Sleep button for 3 seconds.
B. Without releasing the Power button, also hold the Home button for 10 seconds.
C. Without releasing the Home button, release the Power button but Keep holding the home button for another 15 seconds.
9) Now you will have wait till redsn0w finishes installing the ipsw file on your iPhone/iPod touch.
10) That’s it. You’ve jailbroken your device.
Please note: If you have a newer iOS device (New iPhone 3GS, iPhone 4, iPod touch MC version/3g/4g) and you turn off your iPhone/iPod or the battery runs out, you will have to connect your iOS device to the pc and run redsn0w.exe the same way, just clicking on “run boot tethered right now” instead of “install cydia” on this screen:
Remember to back up your SHSH Blobs again on iOS 4.2.1 for the future.