Jailbreak iOS 4.2.1 GM with Redsn0w

The download of iOS 4.2.1 GM just became available to developers, but the jailbreak community has moved quick and determined that existing versions of redsn0w can indeed jailbreak iOS 4.2.1 GM. The downside is that the existing version of Cydia crashes on a jailbroken iOS 4.2.1, meaning you’d have to install apps through SSH. Unless you’re determined to be on the cutting edge of iOS and jailbreak releases, it’s probably best to avoid trying to jailbreak iOS 4.2.1 for now and wait for a new version of Cydia to be released.

If you are looking to jailbreak iOS 4.2.1 use redsn0w 0.9.6b4 instead.

The process to jailbreak iOS 4.2.1 GM with redsn0w 0.9.6b2 has been confirmed by RedmondPie to work on an iPhone 4, and while it’s a little screwy it does work. You will need iTunes 10.1 before getting started, here are the directions:

• Download redsn0w 0.9.6b2 for either Mac and Windows
• Download iOS 4.2.1 GM and iOS 4.1 IPSW (here are iOS 4.1 IPSW downloads if you need them)
• Update/restore to iOS 4.2.1 GM firmware using the IPSW
• Launch redsn0w 0.9.6 and direct it to the iOS 4.1 IPSW file
• Select that you want to Install Cydia, and click Next
• Turn off your iPhone and make sure it is plugged into your computer
• Follow the directions to place your device into DFU mode so that redsn0w can install the jailbreak
• When finished, the device will auto-reboot and it will be jailbroken on iOS 4.2.1 GM

While it’s exciting that the latest update has already been jailbroken, the lack of a functioning Cydia app makes it impractical for most iPhone and iPod touch users.

If you are using the final version of iOS 4.2.1, a better solution would be to download redsn0w 0.9.6b4, but it provides a tethered jailbreak for most devices.