HOW TO: Jailbreak iOS 4.2.1 With Redsn0w 0.9.6b4

Today, the iPhone DevTeam released a new update to redsn0w which will jailbreak iOS 4.2.1. Well yeah, but don’t get too excited, because most of iOS devices will have a tethered jailbreak. Read carefully before using this tool….

NOTE: using redsn0w you will upgrade your baseband therefore you won’t be able to unlock ( possibly ever ). If you need to unlock your iPhone, don’t even think about using this tool.

NOTE: using redsn0w 0.9.6b4 you can jailbreak iOS 4.2.1 , but some devices will have a tethered jailbreak and other will have an untethered jailbreak. A tethered jailbreak means that everytime you need to reboot your iOS device ( because it is required by a newly installed package, or you run out of battery ), you will find yourself with a factory state iOS device. The jailbreak isnt gone, but you will need to connect your iOS device to your Mac or PC and boot it using redsn0w. It’s a pain in the ass, so really, stay away…

NOTE: read everything carefully. If you don’t understand the process, or something might be a concern to you, just be patient and do not use this tool.

NOTE: the process is identical on both Mac OSX and Windows, and also identical with previous redsn0w releases. The images used in this tutorial are from previous redsn0w tutorial, so do not be alarmed. Read the text though… don’t just stare at the pretty pictures.


  • If you have an iPhone3G, older iPhone3Gs, and non-MC iPod Touch 2G you are good to go. The jailbreak will be untethered.
  • If your iOS device is not in the list above, you can still jailbreak it, but you will have a tethered jailbreak.

to make this clear:

  • iPhone 3G devices – no problems
  • iPhone 3Gs devices – if you have newer bootrom, your jailbreak will be tethered. If you have older bootrom, you will not have tethered jailbreak.
  • iPhone 4 – tethered.
  • iPod 3/4 – tethered.
  • iPod 2 – MC model tethered, older model not tethered.
  • iPad – tethered.

You need:

  • redsn0w 0.9.6b4 Mac or Windows
  • iOS 4.2.1
  • iTunes 10.1


1. Restore your device with a stock iOS 4.2.1 firmware. ( again, by doing this you will loose the ability to unlock!!!)

2. Run redsn0w, and click on browse. Browse for the stock iOS 4.2.1 and open it

3. Wait for redsn0w to recognize it and click ‘Next’

4. On the next screen select what you want to be installed on your iOS device(s). By default, Cydia and ‘enable battery percentage’ is selected. I suggest you deselect battery percentage and everything else, and just install Cydia. This will improve ( a bit ) the overall speed of your device – if you are on a iPhone 3G. If you choose to “Enable battery percentage”, you actually toggle that off and on via Settings->General->Usage.

IF you only need to restore with a custom firmware, deselect everything, and select only “Just enter pwned DFU mode right now”

5. redsn0w will ask you to turn your device off. If it’s not already off, plug it in FIRST and then turn it off. Click next to continue

6. Now, you will need to put your device in DFU mode. Follow the instructions on the screen.

7. Wait a few seconds for redsn0w to do its thing, and you are done. You can close redsn0w because everything else it’s happening directly on the device.

NOTE: Any Windows users seeing “Waiting for reboot” for too long (more than 20 seconds or so), please try “shaking” the JB process by unplugging then replugging your USB cable (while letting redsn0w continue to run). Also, try using a USB port “closer” to your computer (as opposed to on your monitor or behind another hub).

Tethered boot how to:

If you have a tethered jailbreak, and your iPhone needs to reboot, you will need to use redsn0w to reboot it. Let’s take a look at how to do it:

1. Open redsn0w 0.9.6.b4 and click on browse. Look for iOS 4.2.1 that you saved on your desktop and select it…

2. Now, select ‘Just boot tethered right now’ and click next…

3. Follow the directions on the screen to put your iOS device in DFU mode…

4. That’s it. Welcome back…