Tutorial: How to Jailbreak Your iPhone iOS 4.2.1 with RedSn0w

By , Nov 23, 2010

RedSn0w was recently updated to jailbreak iOS 4.2.1. While this is excellent news, it doesn’t come without its drawbacks as only the iPhone 3G, older iPhone 3GS, and non-MC iPod touch 2G get the untethered jailbreak.

Other devices get a tethered jailbreak, which means that every time you reboot your iPhone, you will have to plug your iPhone in your computer, and launch RedSn0w to start your iPhone. Hopefully the Dev Team will come up with a way to bypass this soon.

If you are an unlocker, you should not update to 4.2.1 yet. You will lose your chances of unlocking. Wait for PwnageTool, which should be updated relatively soon.

This step by step guide will show you how to jailbreak your iPhone iOS 4.2.1 with RedSn0w. This tutorial was made using an iPhone 3GS but the steps are the same, no matter what device you are using…

Step 1: Make sure iTunes is updated to its latest version. Make sure your iPhone is on 4.2.1. If not, update it via iTunes.

Step 2: Download RedSn0w 0.9.6b4 and the firmware for your device from our downloads section.

Step 3: Launch RedSn0w and browse for the firmware you downloaded in step 2.

Step 4: Select to Install Cydia.

Step 5: Make sure your iPhone is turned off and plugged in your computer. If it’s not, plug it in, then turn it off. Click next, and be ready to get your iPhone in DFU mode.

Step 6: Hold the Home and Power button together for 10 seconds. Release the Power button while still holding the Home button for a few seconds.

Step 7: Your iPhone will run lines of codes. When it’s done. Click Finish. You’re done!

Now if you have a newer device such as the iPhone 4, every time you reboot your iPhone, you will have to launch RedSn0w and choose the “Just boot tethered right now” option to boot your iPhone.

There is currently no unlock for iOS 4.2.1 but we will keep you updated as soon as it is released.

Any question, feel free to ask below.

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  • Andrew

    i download my ipod firmware but it looks like a file and not like the block plus when i start redsn0w the file doesnt even show up anywhere on my computer

    • Gina

      Dont unzip, Just click on the zipped file and change the extension to .ipsw then it should be the white block.

      • Adrian

        How do I change the extension to .ipsw? I’m having the same problem as Andrew

      • jon

        i’m having the same problem. when i change the extension to .ipsw, it remains as the file and doesn’t change to the white block. can anyone help me?

      • mike

        dont change the extension just add “.ipsw” to the end of the file name and click save

      • Amy

        Download the firmware from firefox not explorer. It will download as a .ipsw file not zip.

  • GASPONE

    Don’t forget that you must “just boot tethering right now” right after finishing the JB. The phone will boot, but Cydia will have a gray icon, and not work… Have to re-run RS….

  • kyunghan

    how and where can u install it and jailbreak my iphone 3Gs . please help me

    • angel

      go to this person on youtube very good video on how to do it right, hope this help he is pretty good at explaining.http://www.youtube.com/user/EverythingApplePro and then his new video isDowngrade iOS 4.3/4.2.1 To 4.2.1, 4.1 Firmware On iPhone, iPod Touch & iPad

  • David N

    Everytime I do it redsnow develops an error and has to close? Any ideas?

    • Mike P

      Fixed!

      Redsnow devolps an error? Right click the redsnow.exe and change the compatability to win95 and then run it as an administartor. Worked for me!

  • http://www.iphoneunlock.asia steve

    Nice tutorial mate i will try this now thx for ur help

  • frank

    how do u install the .ign games they give me an error when they install.

  • bquick27

    any ideas on why it will not read my SIM after i Jailbreak it?

  • rajiv

    I have an iphone 4.2.1 and recently did a successful jailbreak by following the easy instructions with redsn0w9.6b4. The problem i’m having is that when i turn my phone on, i get the white apple icon and can”t get to my homepage unless i hookup to my computer and rebbot the phone using Redsn0w.
    Is this a problem or is this something i will have to do each time?

    Please help me

    • Teresa

      that’s what is meant by tethered. everytime ur phone turns off you’ll need to run redsnow and choose just booth tethered

  • Danny

    Rajiv… What you did by using Redsn0w called “Tethered Jailbreak” which means that everytime you reboot your iphone – you’ll need to connect it to your computer.

    I have no idea when they going to expose the untethered jailbreak… till then you’ll have to deal with it.

  • Kiran

    I have the iphone 3gs. How do i know if its the old one or the new 1? :S

  • adel s. badwilan

    Please release the green to escape from iOS 4.2.1, Jailbreak,

  • neel

    this is bullshit

    duznt work

    evrytym u start jailbreaking it says redsnow stopped working unexpectedly

    jailbreak not done successfully

    can any1 help

  • andy

    hi guys, i have installed my iphone’s 4.2.1 firmware but how can i change the zipped file to white block? i tried ipsw but didn’t work for me.

  • David

    I tried this…downloaded what I needed, was going fine until Redsnow developed an error and had to close, tried several times after re-downloading redsnow and the 4.2.1 firmware. In the end I had to downgrade to 4.1, and jailbreak using limera1n, this has worked fine. And i managed to recover contacts and messages too.

    • Dani

      How did you downgrade? I tried and iTunes crashed on my leaving my iPhone in restore mode.

      • Robert

        Do you have your SHSH stored with Cydia or on your computer? If not, you can’t downgrade.

  • Jessica

    I have an older iphone, 3G, which has the updated firmware of 4.2.1

    I am needing to jailbreak it and unlock it being I am out of the country for school purposes, and will be going back and forth over the next few years. So I figured this is the best option for me. But I am curious … since at the top of the article it says to wait to update to 4.2.1 otherwise you loose your chances to unlock it, I am wondering if I jailbreak it, can’t I still unlock it? I already had updated to the 4.2.1 firmware before now, reading this?

    Thanks!!

    • Robert

      If you upgraded to the full 4.2.1, it will have upgraded your baseband to 5.15.04, and there is currently no unlock for that baseband.

  • joe

    Follwed everything for 3g, cydia is installed but it is not taking the sim. No error, no warning. It says no service.

  • Amber

    Can I do this using windows??

  • Nick

    Can I do this using windows?

  • Matthew fenwick

    Hello I hav a iPhone 3GS I want to jailbreak, I have the model updated to 4.2.1- checked in settings and it is a MC model. Does this mean if I jailbreak my phone it will be the tethered version?

  • jewel

    ihave iphone 4 version 4.2.1
    so do i need to update again ?
    if no then what to do
    pls help
    i have spending more than 3 days on this topic.

    • jewel

      hi guys, i have done this method, its working on my iphone4 – 4.2.1, but when i install some apps from cydia and i restart springboard, its says your springboard is crashed and ur mobile is running on safe mode. and every software i have install from cydia all gone. when i restart its work fine. but most of the time i go to cydia something happen (like crashed some apps), and its run on safe mode, but my problem is when i restart, i have to do it from my computer( same method as given above), so when i go far way from my house, then how? and also all the time its dosnt restart perfectly it takes 3-4 times, i think my home button & power button will be damage.
      so pls any solution
      and sorry for taking too much time

  • ramz

    when would be the jailbreak for ios 4.2.1 ……by PwnageTool launched??

  • RM

    hi, when do we get an untethered jailbreak for iphone 4 ios 4.2.1……thanks and am sure it will happen soon knwoing you guys!! thanx

  • jonathan

    Hi..i have a factory unlocked iphone 4 v4.2.1 …can i jailbreak through this method ???????thanks

  • Yan

    IOS 4.2.1. Untethered Jailbreak by chronic-Dev team. I see on You Tube

  • adel s. badwilan

    http://greenpois0n.com IOS 4.2.1 Please help in the installation

  • Ric

    Hi I got an iPhone from the us and I live in Mexico now . Is the jailbreak going to help me get sevice with the Mexican phone company?

  • JHON

    i have followed all the steps but ir frezes ondownloading jailbrak data

  • Mariano

    Hi, just done the jailbrake on my 3gs, but cydia grey app wont start, any ideas?

  • martin

    It stop loading at reboot …

  • yasser

    Hello, somebody is going to sell me an iPhone 3g restored with the latest iOS and baseband. You think I will be able to jailbreaked and unlock right now? Thanks I will appreciate your help.. he restored yesterday by itunes

  • yasser

    Hello, somebody is going to sell me an iPhone 3g restored with the latest iOS and baseband. You think I will be able to jailbreaked and unlock right now. Thanks I will appreciate your help.. he restored yesterday by itunes

  • waheed

    Hi all
    I upgraded my 3GS new bootrom with 06.15.00 BB to 4.2 using redsn0w beta 5 version, initially everything went fine, and it also unlocked using ultrasn0w. But after a few hours the phone turned off. Now when i try to boot it from redsn0w using “just boot tethered now”, it hangs in to a white screen. Thats it. tried restoring methods but get error 1600 or 28. I have also tried ireb but failed.
    All i can see is either a full white screen or a black screen, Please help, its been days i am without my phone

    • Robert

      You can’t restore a normal 4.2.1 IPSW with that baseband upgrade. Start from scratch and run the whole redsn0w JB again.

  • Wally

    Jailbreakme.com is an excellent source also. Can anyone tell when would they be able to jailbreak 4.2.1

  • http://none Wally

    Jailbreakme.com is an excellent source also. Can anyone tell when would they be able to jailbreak 4.2.1.

  • Tyler

    Cant seem to get into uf mode or whatever. it says no device foud even tho im doing it exactly the way it says, please help me?

  • Tyler

    dfu mode*

  • Robert

    http://www.youtube.com/watch?v=bITIiGswjFI

    If you’re phone is plugged into your computer, and iTunes is running, when DFU mode is entered iTunes will detect it and pop up a dialog box that says you have a device that needs recovery. When in DFU mode, the screen will be black.

  • Christian Armenta

    I’m having problems jailbraking iOS 4.2.1 with redsn0w
    on redsnow it stays on “uploading ramdisk” forever and doesnt continue! what do i do!??

  • buda85

    I am also stuck on “uploading ramdisk” any tips how to fix this?

  • Tee

    Hope to get this clear – jailbreak my iphone 4 based on 4.21, cydia crashed when clicked on, safari not working too, wonder how many of u met the same? btw, anyway to circumvent these problems? thks.

  • Pooface

    I dunno the only issues I had with i4 iOS 4.2.1 was if I didn’t hold my home button till after reboot it would crash

  • ansh

    I updated my 3g phone to 4.2.1 through itunes, will i be able to unlock and jailbreak it again..

  • Dani

    My iPhone wont turn on after I installed Winterboard. Its just sitting on the Apple start screen. Any help? Please.

  • Ryan

    I done exactly all this n got my new fone 4.2.1 jailbroke but when I went to open the cydia app it wouldn’t let me open it and my safari woudnt work either! Any suggestions pls help. It’s the 4.2.1 and 05.15.04 firmware

  • john

    IPSW cannot be regognized :( :( help plz

  • andy

    Worked for me , THANKS!

  • Sebastian

    this worked !!! just reboot ur phone sadly it got stuck in restore mode twice but it did work the 5th time!!!

  • Robert

    GreenPois0n RC5 untethered jailbreak was just released. Works on all 4.2.1 for all iOS devices.

    Get it at GreenPois0n.com, or a mirror.

    • Al

      I don’t think greenpois0n works on a 3G w/ 4.2.1 … I’ve been trying to JB mine that way for over 24 hrs, now.

      I’ve restored “to factory” w/ iTunes about a dozen times.

  • Bona P

    i couldnt get red snow working, i put it in dfu mode and tried installing cydia, and the phone was unresponsive. not sure im using the right version, rc8 0.96, had to restore twice. any advice ? or should i just wait the the servers to be back online?

  • gunzz99

    i did everything
    all is fine
    but the cydia/safari
    just wont open
    n cydia is a white/grey block with no icon
    do i have to connect it to the onternet then open it…??
    plz help

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