Want to downgrade iOS 4.2.1?
We posted a jailbreak for iOS 4.2.1 GM earlier. However, we warned that Cydia does not work yet, and it won’t until the iOS 4.2 is released to to the public. Because of that, some may not see much of any reason to keep iOS 4.2.1.
Note: If you are on an iPad, iPhone 4, iPod Touch 2G (MC Model), 3G or 4G and don’t have your SHSH blobs saved on Cydia, you cannot downgrade.
You will also need to download TinyUmbrella.
Well, here’s how to downgrade in case you find yourself not liking it:
2) Put your device in DFU Mode. Read our article here.
3) iPhone3GS, iPHone 4, iPAd, iPod Touch 2G, 3G and 4G only. If you have an older model device, skip to step 4: These devices safe their SHSH blobs on Cydia for the firmware you are downgrading on.
A) On Windows, Find the “hosts” file under – C:\Windows\System32\drivers\etc\
B) On Mac, hit Shift+Command+G to bring up the “Go to Folder” window and find the “/etc/” directory.
C) You will open this file in Notepad (Windows) or TextEdit (Mac) and add: 18.104.22.168 gs.apple.
D) Now save the file.
You may need to run notepad as an administrator by right clicking the icon and selecting “Run as Administrator.
On the Mac, you may have to save the file to your desktop then replace the original file when done.
4) Now restore your device with the ipsw you downloaded earlier. This is done by hitting Alt and clicking Restore. You will then choose the ipsw file you want to use for the update.
5) Your device will be stuck in recovery mode. Launch TinyUmbrella and click “Exit Recovery” and your device should restart normally.
After that, you should be running on the older iOS firmware, and can now jailbreak your device. Read here for more info on jailbreaking iOS 4.1 You can also jailbreak the iPad on 4.2 with this tutorial.