RedSn0w is a jailbreak tool developed by the Dev-Team. Originally called QuickPWN, this jailbreak tool was then renamed, and has now become the favorite tool for most of the jailbreakers. RedSn0w works for both Mac and Windows.
You can grab the latest version of Redsn0w from HERE
(Make sure you get the right one for your OS)
FAQ
Which Devices Can Be Used With Redsn0w?
iPhone 4S
iPhone 4
iPhone 3GS
iPhone 3G
iPad 2
iPad 1
iPod Touch 4G
iPod Touch 3G
iPod Touch 2G
What iOS versions can be used with redsn0w?
iOS 5.1.1, iOS 5.1, 5.0.1, iOS 5, 4.3.5, 4.3.4, 4.3.3, 4.3.2, 4.3.1, 4.3 4.2.1, 4.1, 4.0.2, 4.0.1, 4.0, 3.2.2, 3.1.3
Some of these iOS can only be jailbroken tethered, depending on your device.
I'm on Windows and redsn0w says it stopped working. What should I do?
Unplug your device and close redsn0w. Hold power and home button on your device until screen flashes. Now, Connect the device to the computer and start redsn0w as usual.
What else can I do with redsn0w apart from jailbreaking?
Not only can you jailbreak, you can also boot tethered devices with tethered jailbreak, preserve baseband, manage shsh blobs, install custom boot logos, etc.
What's the diference between an untether and a tether jailbreak?
An untether jailbreak is the jailbreak everyone anxiously awaits for. Why? Because it doesn't require you to boot tethered everytime you reboot your phone or its battery dies. The latest untether jailbreak is for 5.1.1 firmware on all devices.
A tethered jailbreak is the same as an untether jailbreak except for the fact that you have to connect the device to a computer and use a tool like redsn0w to boot tethered and be able to boot it. There is a cydia tweak called Semitether which allows the device to reboot while jailbroken tethered but with some limitations.
How can I put my device in DFU mode?
Connect the device to the computer, hold the home and power button for 10 secionds. Then without releasing the Home button release the power button and continue holding the Home button for 10 more seconds. Now after ten seconds have passed release the Home button and the screen should be cmopletely black. You've succesfully entered DFU mode. If you see the iTunes logo you did it wrong.
Jailbreak
Jailbreaking your device is very easy. You just have to follow a few simple steps in order to get in DFU mode and redsn0w will do the rest. You can do tether and untether jailbreaks with redsn0w, depending on the firmware your device has. Remember that to jailbreak your device you must have iTunes installed on your computer.
Here are some quick instructions to get your device jailbroken:
1. Download and launch redns0w
2. Click jailbreak and make sre your device is plugged in and turned off
3. Click next and follow the instructions to put your device in DFU mode, then click jailbreak
4. That's it! If your jailbreak is tethered remember to go back and boot tethered in order to use cydia
Downgrade
Redsn0w also has the ability to downgrade A5 devices like the iPhone 4S or iPad 2 to 5.0.1 firmware. As usual, you'll need 5.0.1 SHSH blobs saved to downgrade.
Here are some quick steps to downgrade:
1. Download a 5.0.1 and 5.1.1 ipsw files
2. Put device in DFU mode, then open redsn0w and select 'Extras' then click on 'Even More', then select 'Restore' and browse to the 5.0.1 ipsw followed by the 5.1.1 ipsw
3. Now you need to get the 5.0.1 SHSH Blobs. Click on the 'Local' button if the SHSH blobs are stored on your computer or 'Remote' if they're stored on Cydia.
4. Redsn0w should now do all the work
Features
Preserving Baseband- The option to preserve baseband is very useful for iPhone owners that are currently on an unlockable baseband and want to update to a newer firmware. Those of you that have factory unlocked phones don't have to worry about preserving basebands.
Pwned DFU - Pwned DFU allows you to use iTunes to restore your deevice with a custom firmware to preserve baseband. That's the only difference betwen Pwned DFU mode and DFU mode.
Recovery Fix - The Recovery Fix option is useful when you receive recovery errors when performing restores in iTunes.
Fetch - This option allows you to submit your SHSH Blobs to Cydia. Your device must be in DFU mode to use this feature.
Verify - This options allows you to check what SHSH Blobs are available on your device. This feature also needs your device to be in DFU mode.
Query - This feature queries the Cydia server about all the SHSH blobs available to a device. This feature does not require your device to be in DFU mode.
Stitch - This feature allows you to stitch SHSH blobs to a firmware/ipsw file so you can use it even if Apple is still not signing that firmware anymore. This is a very useful feature and is the only way to downgrade on iOS 5. With this you can even restore your device without updating it at the same time.
ECID - This will list all of the ECIDs for all devices used by RedSn0w. The ECID is an identifier unique to every device.
Boot args - This feature allows you to run commands while running redsn0w. Not very useful to the average user.
Boot Logo- The Boot Logo option allows you to replace the default Pineapple logo. The images must be in PNG format for this to work.