Jailbreak iOS 4.2.1 Guide for iPhone 4.2.1, iPod touch 4.2.1, and iPad 4.2.1
If you’d like to jailbreak iPhone 4.2.1, iPod touch 4.2.1, or iPad 4.2.1, you can do so by following the guide below. Currently the only tool that supports iOS 
4.2.1 jailbreak right now is redsn0w (by iPhone Dev Team).
The other jailbreak tools: greenpois0n (by Chronic Dev Team), and limera1n (by Geohot) haven’t been updated to support the jailbreak for iOS 4.2.1 yet.
IMPORTANT: We recommend that only iPhone 3G, and older iPod touch users jailbreak. This jailbreak is only untethered for the older iOS hardware. All of the newer devices are tethered, meaning you will need to re-jailbreak each time you reboot your iDevice. If that is fine with you, then go on and jailbreak.
- Download iUserbar new – click here (works on Firefox, Internet Explorer, and Safari)
- In iUserbar new, click the “Downloads” button and then click on your iOS 4.2.1 firmware to download it.
- In iUserbar new, click “Downloads” and click on Download redsn0w to download redsn0w.
- Now open redsn0w, and click the Browse button.
- Locate your device’s IPSW file that you downloaded in step 2 and click Open.
- The redsn0w window will have the “IPSW successfully identified” message. Click the Next button to continue.
- redsn0w will ask you to “Please select which options you would like to have“. Make sure the Install Cydia box has a check on there and then click Next.
- redsn0w will ask you to make sure your device is both OFF and PLUGGED IN to your computer. Make sure you plug in your device in to your computer and then turn it off. Click Next once you have done this.
- redsn0w will now ask you to connect your device in DFU mode.
- Hold down the Power button for 3 seconds
- Without releasing the Power button, also hold down the Home (bottom center button) for 10 seconds
- Without releasing the Home button, release the Power button BUT KEEP holding the Home button for 30 seconds
- If you don’t do this properly you will get a DFU Mode Failed message and you’ll have to go back to step one.
- Once this process is complete, your device will restart and it will have the Cydia icon!
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113 Comments
OK, I got everything going – lots of thanks to all those who commented with suggestions (renaming the .zip file was the first one, second one was running the redsn0w file in XP compatibility, as administrator). The jailbreak was successful (sortof), now when I click on Cydia on my iPhone it doesn’t want to open. It makes the screen flash white once (very briefly) and then goes back to the iOS home screen. What to do?
found the answer! i just needed to re-run redsn0w and select “just boot tethered”! wo hoooo
How do u re run it?
and where is ‘*just boot tethered*’
Rename teh file to what?
don’t need to rename the file. when redsnow is browsing for the ipsw, go to the location you saved it to. it will be looking for *.ipsw . there is a text entry box beside it, just type in *.zip and it will show the zip file, select it and click next. it will work.
Hi,
Everything works like a charm, excpt that my iPhone 3G runs into what appears to be a loop.
Boots up, shows the Appel logo, the little loader appears, then the screen flashes something and the device reboots.
I have also removed the sim card, reflased but the same problem keeps on happening. What I do remember is that my Wifi was left on. WIll keep on playing with it.
No funny selections have been made, just the Cydia icon was added.
Thanks for the great work you guys have done so far! Believe me, we really appreciated it!
Good News!
Following the previous loop I was stuck in, I have now managed to get pass this problem and was able to update to 4.2.1 with Cydia enabled :-)
I did the upgrade directly from 3.1.2 to 4.2.1
It failed and I believe that it could have been related to the version of the Boot ROM. Not mentioned anywhere.
To get out of the loop, get you phone into USB Loader or DFU mode.
Restore the 3.1.2 IOS using ITUNES, latest one worked for me.
Once restored, you phone will need to restore its settings from backup. You can do that, but should not be required.
Using ITUNES, upgrade the IOS to version 4.1 Then follow the same steps of restoring your settings.
Following a succesfull upgrade and restore of 4.1, refer to the above normal instructions and upgrade your iPhone to 4.2.1 with Cydia, multi-tasking enabled, etc.
Works like a charm and just needed a bit of troubleshooting :-)
Again, thank you guys! Great work!!
I cant locate my device’s IPSW file that I downloaded in step 2… Can anyone help me?
How do you upgrade to a higher firmware without upgrading the baseband.
Redsnow says it is for your current firmware only.
i got a 3GS – SN: 88926
everything work fine except that
my phone cant find the carrier
what should i do??
same
Hello, i´ve jailbreaked my ipod touch. And after it rebooted the cydia icon was there. And then i tried to click on it. It closed after 1 second. Do you know what the issue is? Please help me!!!
ok so… i started up redsn0w and i browsed for the 4.2.1 firmware file. but after it prossesed the firmware a message came up that said, it doesnt support mc models yet.
so can someone please help me…
hey, redsn0w always gets stuck on exploiting limera1n when i try it, and its really p-ing me off, anyone got a fix
Mine too. I found out that my ipod touch 3g 8gb is actually a 2g mc model. Redsn0w dosent work for MC models yet :/ wondering when it will be fixed?
Ok this is happening to mee too.
So I just cancel and retry while its still in DFU mode and it got a couple percent furhter then turned my iPod on.
Then I put it back into DFU mode by myself and try againg then it goes up to the reboot phase and gets stuck.
Then I use an old greepois0n jailbreak download to get it to revoot and it worked, but Cydia wasnt on my iPod. And I figure out how to jailbreak now?
ARRRRRGGGGGG
I’ve been trying to jailbreak my iphone 3G for almost a week, not able to. Redsnow keeps freezing at ramdisk.
I’ve tried all the hints, admin, compatibility modes, followed the step by step instructions… over and over.
NO LUCK.
will someone pllllllsssss help me???????
Help please!!! Mine keeps freezing on the pineapple logo. I have tried few times now but is not working. Is still freezing on the pineapple. What i am gonna do? please help!!
I have an ipod touch 4g 4.2.1
how to unlock sim after jailbreaking it.
i have tried repo666.ultrasn0w.com sources but no use.
did you update your ios through itunes? when update on there, it also upgrades your baseband to an unlockable 5.14.04 or 5.15.04. you either have to update to 6.15 or remain unlockable until an update comes if one ever does
I have a 3GS – SN: 8893569 and it’s all working well, but it doesn’t recognize my SIM card and cannot find my carrier.
same problem…everything works well past the dfu part, then the phone just wont recognize the sim
Alright. So i downloaded the 4.21 update as a ipsw. Ran Redsn0w in xp compatibility mode and as an administrator. it worked out all good and told me to put my ipod in DFU. once i did that, it started working, but it gets stuck at exploiting with limera1n for ridiculous amounts of time. whats the deal with that? what should i do
WAGWAN
Yeeh, my iPhone 3G is jb’d on 4.1. To update to 4.2.1, do i need to restore?
Please reply ASAP yehh.
SAFE
Hi every one!
I’ve downloaded the toolbar but it wont let me download the 4.2.1 software from the toolbar… Please help me…
Thank you so much!!!
Ok, so I have been reading up on this because I am not the only one with this problem. I have the ipod touch 3g 8gb only to find out apple scammed those who bought it and its really a 2g. So when I would try to jailbreak it with the 3g firmware it would always get stuck on limera1n part. redsn0w dosent support ipod touch 4.2.1 MC firmware, and idea when this will be available?
i have a lock iphone 4 with BB 2.10.04
when can i unock it?
Hello;
I have an iphone 3g 8GB, but whith only 6,9GB after my latestes jailbreak ios 4.1. whith greenpoison Saved SSH in cydya.
Now when i try to update to 4.2 whith redsnow, the process goes fine, but it doesnt update to 4.2.
Can you please help me? Why i only have 6,2 GB, and why can i not update to IOS 4.2.
Since the System HD and HD for the apps is diferent . you have to delete some big apps before you will update your iphone to 4.2.1
iPhone4 on 4.2.1 – When running redsn0w (as admin in XP mode) I get stuck at the ramdisk screen and have to do a full restore on the phone, any tips?
Happy Holidayz!
I have an iPT2g MC model and I know I am unable to jailbreak it but everyone said the dev team would make a jailbreak for it now but they havnt. I was also told that I could use tiny umbrella and downgrade but idk… Any ideas?