iPhone Dev Team has recently rolled out Redsn0w 0.9.7b4 for Mac users to untether iOS 4.2.1 jailbreak. This fourth beta will terminate the need to install and run a separate program for usbmux. This beta untether is currently a backup plan from the Dev Team for iOS 4.2.1 untethered jailbreak on iPhone 4, iPod Touch 4G and iPad, but open only to testers.
This fourth beta has also fixed the race condition in the user interface, as it was long idea to cause Redsn0w to crash during the “Preparing JB Monte Files” option. Keep in mind that the Redsn0w 0.9.7b4 is still not meant for general consumption yet and currently meant for those who interested in beta testing. The fourth beta is available only for Mac users right now but the next update will assume the Windows support.
bear in mind that the current untethered version requires access to iOS 4.2b3 and its SHSH blobs must be saved. Dev Team is suggesting the beta testers to test after a fresh restore. Hit the below links to get this fourth beta.
Download: Redsn0w 0.9.7b4 For Mac OS only
Source: Dev-Team Blog