Wednesday, July 11, 2012

Dualboot CM9 on SGS3 LTE (Sprint, T-Mobile, AT&T)

This method CM9-on-EMMC allows you to run CM9 on your SGS3 LTE while leaving the stock ROM and kernel intact.  The alternate ROM is stored in /sdcard/multiboot/CM9 of the "internal sdcard" storage.  Booting the alternate ROM is temporary.  Reboot the phone to return to the standard ROM.

Supported Phones
Currently only Sprint SGS3 CM9 nightly builds contain the requisite kexec kernel support. Other SGS3 LTE variants can be easily supported later when they gain kernel support.

  • Install CWM SGS3 LTE.  You must have version 5+ for kexec support.
  • Download the following files and put them in the internal storage, Samsung's ROM calls it /sdcard
      • Mirror [1] [2]
      • md5sum cd6bdf2e37299641d81aa135dc58814c
      • Check this page periodically for updates as we plan on improving this toolkit in the future.  TODO list:
        • Automate internal sdcard bind mounting/unmounting.
    • CM9 nightly build from
      • Sprint SGS3 is d2spr.
      • See the known bugs here.
    • gapps
  • Your SGS3's internal storage must have at least 1GB available.
Important Warnings!!!
  • Do Not Install Google Wallet: Google Wallet's NFC Secure Element has the potential to become permanently damaged if you switch ROM's or reset data without first instructing the Google Wallet app to reset itself.  In order to avoid errors and the potential for permanent phone damage, we recommend not installing Google Wallet within CM9-on-EMMC.
  • Do Not Install ROM Manager: It can cause unexpected problems if you attempt to use the ROM Manager app to flash any .zip from CM9-on-EMMC.

Install CM9-on-EMMC
  • Boot into CWM Recovery (TeamEpic's v5+)
  • install zip from sdcard > choose zip from internal sdcard >
    • Flash
    • This will create and format empty disk images in /sdcard/multiboot/CM9/
  • choose zip from internal sdcard > multiboot > CM9 >
    • Flash
    • This reboots into the red colored FakeCWM.
  • choose zip from internal sdcard >
    • Flash
    • This makes the internal sdcard available in FakeCWM.
  • choose zip from internal sdcard >
    • Flash the CM9 nightly build .zip.
    • Optionally flash gapps.
Upgrade CM9-on-EMMC
  • Boot into CWM Recovery v5+.
  • Flash multiboot/CM9/ to reboot into Red FakeCWM.
  • Flash CM9 update zip.
  • Flash multiboot/CM9/ in order to reboot into CM9.
How to Boot CM9-on-EMMC
  • From either CWM v5 or FakeCWM, choose zip from internal sdcard > multiboot > CM9 >
    • Flash
How to Reboot into Standard ROM
  • From CM9, if you Reboot or Power off, the next time your phone boots it goes straight into CWM.
    • Choose "reboot system now" and will reboot into the standard ROM.


  1. Excellent work bbelos + mkasick!

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  4. I can verify this works (with some edits) on the verizon sgs3 sch-i535

  5. Would just deleting the multi-boot folder reverse this?

  6. Yes, delete the folder + it's gone completely, you're back to your stock ROM daily still have the option of booting the multi-boot file at some point in the future to 'test' other newer builds that may intrigue you prior to doing a complete data wipe for a clean install.

    Personally, am keeping two builds in tandem: Original rooted stock (CWMv5 / ROOTv5 from Team Epic) as well as the dual-boot for Nightly Builds going forward (am currently on Nightly_0714.) The multi-boot is able to store my data for the Nightlies, and from power-off am able to return to my original build, then multi-boot to Nightly Builds.

  7. Is there a way to increase the size of the images created by ? Mine says i have 516MB of space and i filled it up quick with apps.

    1. Well i found one way using Linux. Make sure you are not currently booted into CM9 (reboot into stock if you are). Copy your /sdcard/multiboot/cm9/data.ext4.img to your Linux machine and then copy it back to the same place after executing the following commands.

      [PATH] = path to your data.ext4.img file.
      [SIZE] = amount of space you want to ADD to your .img file (in MB)

      dd if=/dev/zero bs=1M count=[SIZE] >> [PATH]
      e2fsck -f [PATH]
      resize2fs [PATH]
      e2fsck -f [PATH]

    2. I did this as you said and I entered in 2000 (so 2GB), it made the image file very big accordingly, but then it did not give me any more than 400MB when I booted back into CM10 (in my case, not CM9). It transferred back over fine, all the sectors were repaired, it booted fine, etc. Did I neglect to do something?

    3. Started over. Read this thread here for details: and set the sizes to like 800, 1200, 500

  8. I tried flashing and it wont create any folders. no multiboot/ folder anywhere. any thoughts?

    1. same idk whats going on ive tried about 10 times!

    2. You guys need to edit the updater-script in the main .zip. Change the emmc s to sdcard. I can't say this for sure, but I think it has to do with the recovery you're using.

    3. I have no idea what this means, but this issue is also happening for me. I see no "multiboot/" after I run the .zip to set it up. Can we get some support on this issue, as I'm pretty sure I'm not missing any steps in the directions.

  9. im sorry to bother anyone but i'm having a pretty annoying issue with after attempting to use this method, and i would just like to solve my problem, regardless of being able to dualboot or not, so let me start from the beginning

    i. Im stock Factory stock MG2 rooted and had cwm 5+ on SPH-L710
    ii.i followed all instructions to a tee and upon trying to flash my second rom i got an installation abort, error 7 i think, 'expected 4 args instead of 5' or something along those lines. the rom i was trying to flash was the latest nightly 4.3 9/24/2013 CM10.2
    i also attempted rootbox 4.2 and even the TW rom Wicked Sensations, all with the same error. so having not been successful, i proceeded to delete the /multiboot folder and give up on dual booting, until i realized not even 2 mins later, that every single reboot from rom to recovery, reinstates the factory recovery image, i odin the recovery back, and boot directly into CWM after a battery pull and its there, but once i boot into my stock rom, and attempt to boot into recovery again, i go back to the stock recovery, every time, guarantee. i dont know what happened and there was no warning of this possibility, nor have i been able to find a similiar situation by google searching. i really need some help.

    also i can note two half-fixes that only solve one problem, by creating another.
    1. i installed ktoonsez kt747 kernel and it did allow me to keep my recovery, but in exchange i no longer had data???? idk why, or how to fix that
    2. install a custom rom such as rootbox, allowed me to keep my recovery just fine, but i get only 1 bar service, and mediocre data speeds on any cm based rom, apparently a known bug. so basically i just want to go back to where i was originally :/
    i have tried restoring a backup, ive tried doing a fresh odin install of MG2, but i cant seem to get my recovery to stick past a reboot. please help me, you can email me at with any advice as im not sure if i would be notified of a response to this post at all.

    Thanks in advance