redsn0w is a tool for Mac and Windows that provides untethered jailbreaks for iOS versions including:

  • iPhone 4 (GSM): 4.1 through 4.2.1, 4.3.1 through 4.3.3, and 5.0.1
  • iPhone 4 (CDMA): 4.2.8 and 5.0.1
  • iPhone 3GS: 4.1 through 4.2.1; 4.3.1 through 4.3.3 (old-bootrom 3GS untethered on 4.3.4 through 5.0 too); and 5.0.1
  • iPhone 3G: 4.1 through 4.2.1
  • iPad 1: 4.3.1 through 4.3.3, and 5.0.1
  • iPod touch 3rd generation and 4th generation: 4.1 through 4.2.1, 4.3.1 through 4.3.3, and 5.0.1
  • iPod touch 2nd generation (which actually includes devices sold as iPod touch 3rd generation 8 GB): 4.1 (and also 4.2.1 but only on devices with serial numbers starting with MB)

And tethered jailbreaks for iOS versions including:

  • iPhone 4 (GSM): 4.3.4 through 5.0
  • iPhone 4 (CDMA): 4.2.9 through 5.0
  • iPhone 3GS: 4.3.4 through 5.0
  • iPad 1: 4.3.4 through 5.0
  • iPod touch 3rd generation and 4th generation: 4.3.4 through 5.0

redsn0w runs on already-upgraded un-jailbroken devices.

Steps: Download redsn0w for Mac or Windows. Open it, plug your device into your computer, and follow redsn0w's instructions.

If your version of iOS has a tethered jailbreak, this means you need to plug your device into a computer and run redsn0w every time your device boots (such as when it runs out of battery), or else it will get stuck at the Apple logo while booting (or Cydia will crash when you try to open it). To boot tethered: open redsn0w, click "Extras" and then click "Just Boot".

Tips for Windows users: Extract redsn0w.exe to your desktop instead of running it from inside the .zip archive. You may need to right-click redsn0w to run it from an administrator account and/or run it in XP compatibility mode. If you use Internet Explorer to download an IPSW file, you may need to change the file extension from .zip to .ipsw in order to use it.

Note for unlockers: if you upgrade iOS using iTunes, it will upgrade your iPhone's baseband, which negatively affects iPhones unofficially unlocked with ultrasn0w. Instead use redsn0w's "Custom IPSW" feature to upgrade and jailbreak your device while preserving your baseband.