Accompany glide iOS 4.2.1, jailbreak tool for latest iOS began to appear. iPhone Dev Team just updated redsn0w jailbreak tool for 4.2.1 worked for iOS. Newer redsn0w is version 0.9.6b4 that can be used to jailbreak 4.2.1 iOS device. Jailbreak Tool is assembled based Limera1n Bootrom exploit, works of famous Jailbreaker Geohot.But unfortunately jailbreak using the latest redsn0w previous jailbreak is not easy. You will need the intervention of a PC to boot the IOS device under jailbreak.
This jailbreak will 'disappear' if your IOS device is running out of battery or reboot. Of course you have to do the jailbreak again if the device you could die or need to reboot.
Jailbreak type is known as Jailbreak tethered. Interested in trying? Consider the steps IOS 4.2.1 Jailbreak below along with the video. For the record this jailbreak method only works on the iPhone 3G, iPhone 4, iPad, iPod Touch 2G (MC model), iPod Touch iPod Touch 3G and 4G.
This guide will help you jailbreak any device. However, let me first warn iPhone owners relying on Ultrasn0w unlock. An unlock hasn't been release yet for iOS 4.1 or 4.2 and it will be available only after Cydia has been updated to 4.2(in a week's time maybe). So at the moment you should refrain from upgrading to 4.2.1 and not use this guide.
The Redsn0w Jailbreak will offer a tethered or untethered jailbreak depending on the device you own:
- iPhone3G, older iPhone3GS, and non-MC iPod touch 2G: untethered jailbreak
- More recent devices (iPhone 4, iPad, iPod touch 4G): tethered jailbreak (meaning if your device reboots, you'll have to re-jailbreak)
Steps to Jailbreak iOS 4.2.1:
First update your iPhone to the latest firmware by downloading the IPSW file using direct download links here. Use the direct download link as you will require the IPSW file during jailbreak in the later steps.
Open iTunes and press Shift + Update(windows) or Alt + Update(Mac) and point to the IPSW file to update device.
Download latest Redsn0w for your operating system:
Extract and run Redsn0w.

Click on browse and point to the IPSW file and hit Next. Once Redsn0w has prepared jailbreak data select "Install Cydia" and proceed with the onscreen instructions.



Hit Finish once Jailbreak is over.

In case your device falls in the Tethered Jailbreak category, you will need to repeat the steps with "Just Boot Tethered Right Now" selected. If you don't do this Cydia won't work yet. For Untethered devices, the magic is all done.
For tethered devices, it is a little exhausting to repeat this process every time the iPhone restarts but atleast we do have an early Jailbreak.
Video
How To Fix iTunes 1013 Error During iOS 4.2 Upgrade
For those who have used TinyUmbrella before, you may suffer from the error. TinyUmbrella is a great hacking utility for iPhone. You probably used TinyUmbrella for saving SHSH or kicking a problematic iPhone out of recovery mode. As you use the utility, it changes the content of the hosts file in your operating system (i.e. Windows or Mac OS). Unfortunately, the change prevents iTunes from upgrading your iPhone to iOS 4.2 properly and hence it shows the 1013 error.
To fix the 1013 error, you'll need to modify the hosts file and comment out a sentence. Here are the procedures for Mac and Windows.
For Mac User
1. Go to your "Applications" folder
2. Go to your "Utilities" folder
3. Launch "Terminal"
4. Type "sudo nano /etc/hosts" (without quotes) and hit return

5. Enter your password when prompted
6. Use the down arrow key to find the "gs.apple.com" entry. Once the cursor is in front, make sure you comment out the line by entering "#" (no quotes) in front of the text as displayed below:

7. Press CONTROL+O to save the file
8. Press CONTROL+X to quit the editor
For Windows User
1. Open Notepad with Administrative privileges by clicking Start -> All Programs -> Accessories and then right-click Notepad and select to open as Administrator.
2. Click File -> Open and browse to C:\Windows\System32\drivers\etc.
3. Use the down arrow key to find the "gs.apple.com" entry. Once the cursor is in front, make sure you comment out the line(s) by entering "#" (no quotes) in front of the text just like step 6 shown in the Mac's procedures.
4. Save the file.
Restore Your iPhone After the Change
After the change, you can go back to iTunes and hit "Restore" to restore your iPhone. This time, you should be able to upgrade your iPhone properly.

































