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Cyanogenmod 9 for AT&T Galaxy S2 [Installation Guide]


You know your device is famous when it gets an official Cyanogenmod (CM) ROM. The AT&T Galaxy S2 i777 was always a well-known device in the developer community, and now it’s got a shot in the arm as the official CM9 ROM, based on Ice Cream Sandwich Android 4.0.3 has been released for it. Cyanogenmod is a proven name when it comes to providing improved performance along with a multitude of customization options, and CM9 based on ICS will probably be no different.

The ROM is under development and in the nightlies stage, where a new version of ROM is released almost everyday, automatically generated and including the changes made by the developers every day. Do keep in mind though, as the builds are  automatically generated, bugs and errors can creep into the ROM without any warning.

Read on to find out how you can install Cyanogenmod 9 on your AT&T Galaxy S2 i777.


This firmware and the guide below are compatible only and only with the AT&T Samsung Galaxy S2, model number i777. It’s not compatible with any other device and may render an incompatible device unusable. Check your device model in Settings » About phone.


The methods and procedures discussed here are considered risky and you should not attempt anything if you don’t know completely what it is. If any damage occurs to your device, we won’t be held liable.

ROM Info


Developer(s) → atinm/Cyanogenmod team.

Pre-Installation Requirements

  • Important! An AT&T Galaxy S2 i777 with ClockworkMod (CWM) recovery installed. 
  • This procedure will wipe all your apps, data and settings (but it will NOT touch your SD cards, so don’t worry about those). Backup your Apps and important data — bookmarks, contacts, SMS, APNs (internet settings), etc. This Android backup guide would help you.
  • Sufficiently charged battery, at least 50% is recommended.

How to Install CM9 on AT&T Galaxy S2 i777

  1. Download the latest version of the CM9 ROM from the official download page.
  2. Download the Cyanogenmod 9.x version of the Google Apps package. This will install apps like Market, Gmail, etc. which are not present in the ROM by default.
    Download Link
  3. Transfer the downloaded zip files from step 1 and step 2 to the internal SD card on the phone.
  4. Turn off the phone, then boot into recovery mode. For this, press and hold these 3 buttons together until the screen turns on: Volume UP + Volume Down + Power. Keep holding the buttons down till the screen flashes the 2nd time, then let them go. Phone will boot into CWM recovery. Use volume keys to scroll up and down between options and power/home key to select an option.
  5. [Optional but recommended] Perform a Nandroid Backup of your existing ROM, so that you can always restore it from recovery if something does not work out with this rom. To perform a backup, select Backup and Restore –> On the next screen, select Backup again. Go back to main recovery menu after backup is complete.
  6. Now select install zip from sdcard, then select choose zip from sdcard. Scroll to the ROM file on the sdcard and select it. Confirm installation by selecting Yes – Install _____.zip on the next screen. The ROM will start installing.
  7. After the ROM finishes installing, select go back to go back to the main recovery menu.
  8. Now repeat step 6, but this time select the Google apps package (from step 2) to install the Google apps package. After the Google apps package finishes installing, select go back to go back to the main recovery menu.
  9. Select wipe data/factory reset, then select Yes on next screen to confirm. Wait a while till the data wipe is complete. This is important as without this step Calendar sync won’t work.
  10. After the installation is complete, select go back then select reboot system now to reboot the phone.

Updating to Newer Builds of the ROM

As the ROM is in the nightly stage, a new version will come out regularly. To update to newer versions, follow the steps given below.

  1. Download the latest version of the ROM from the development page.
  2. Transfer the downloaded file to the internal SD card.
  3. Turn off phone and boot into recovery.
  4. Select install zip from sdcard, then select choose zip from sdcard. Scroll to the ROM file on the sdcard and select it. Confirm installation by selecting Yes – Install _____.zip on the next screen. The ROM will start installing.
  5. After the ROM finishes installing, select go back to go back to the main recovery menu.
  6. Perform a cache wipe:
    1. Select wipe cache then select Yes on next screen to confirm.
    2. Select advanced, and then select wipe dalvik cache » Yes – wipe dalvik. Then go back to the main recovery menu.
  7. Select reboot system now to reboot the phone to boot into the updated version of the ROM.
  8. [Optional] If you have problems like apps force-closing, etc after updating, boot into recovery, do a wipe data/factory reset, then reboot the phone.

So there you have it. Following the above procedure, you can install CM9 on your AT&T Galaxy S2 i777, based on Ice Cream Sandwich Android 4.0. Visit the original development page for more info and to get the latest updates on the ROM. Share your thoughts on the ROM in the comments.

  • kevin

    why even post this guide odds are if someone has managed to get Clockwork recovery installed on the S2 they already know how to flash a zip file…. Im sure a guide to installing CW would be better served just one mans opinion.

  • srlunar

    Installed it and now my i777 wont start at all… Yeah, wont start

  • Imalilkkm

    why do i get an error message while trying to flash?

    • http://www.theandroidsoul.com/ Kapil

      What error are you getting?

      • Imalilkkm

        NVM i got it to work but now I am facing no Audio, no backbutton, no Data connection issues. any idea?

        • L2867

          i am also getting no audio – added apn manually (twice) but it didn’t save.

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