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CyanogenMod 12.1 Custom ROM based on Android 5.1.1 Lollipop released for Galaxy S2 I9100 [How to Install]

Android 5.1.1 Lollipop is now available to download for the Samsung’s old flagship device Galaxy S2 I9100. Thanks to the custom ROM developers for providing the unofficial CyanogenMod 12.1 custom ROM based on the the latest AOSP release, Android 5.1.1 Lollipop that can be installed on Galaxy S2. With this updated Android OS, CM12.1 comes with many bugs fixes like the signal strength issue.

If you are interested to get Cyanogenmod 12.1 Android 5.1.1 Lollipop custom firmware on your Galaxy S2 I9100 then follow the given guide carefully. Keep in mind that this is just a custom ROM which is released by the third-party developers, not officially released by Samsung. You’ll need a custom recovery like CWM or TWRP recovery install the ROM and Gapps zipped files on your phone.

CyanogenMod 12.1 Custom ROM based on Android 5.1.1 Lollipop

CyanogenMod 12.1 (Android 5.1.1 Lollipop) ROM Features:

This CyanogenMod 12.1 custom ROM featuring Android 5.1.1 Lollipop brings a lot of new features. Here we’ve given the main features of this ROM:

  • Updated CM sources (Android 5.1.1)
  • Fixed signal strength


This guide containing the CyanogenMod 12.1 Android 5.1.1 ROM and instructions are working with only Galaxy S2 I9100. If the model number of your device is I9100 then go ahead, otherwise not. Verify the model number of your device first.


AndroidBlog will not be held responsible for any kind of damage occurred to your Galaxy S2 I9100 during or after the installation process of CM12.1 Android 5.1.1 Lollipop ROM. Proceed at your own risk.


  • Create a proper backup of all your existing data and settings on the phone before proceeding to the installation guide using a recommended custom recovery.
  • Enable USB Debugging Mode on the Galaxy S2 by navigating to Settings > Developer Options.
  • Verify that you’ve properly installed the Galaxy S2 USB Drivers on the PC.
  • The Galaxy S2 should be rooted with the latest version of custom recovery like CWM or TWRP installed.
  • The bootloader of your S2 must be unlocked.
  • Make sure that the battery level of the Galaxy S2 is at least above 80% before going ahead.

Required Files:

Steps to Update Galaxy S2 I9100 to Android 5.1.1 Lollipop with Cyanogenmod 12.1 custom Firmware:

Follow the given step-by-step guide to install Cyanogenmod 12.1 Android 5.1.1 Lollipop custom ROM on Galaxy S2 I9100.

1:- First, download Android 5.1.1 CyanogenMod 12.1 custom ROM ( for Galaxy S2 I9100 on the desktop of the PC.

2:- Connect the Galaxy S2 to the PC using USB data cable and mount its USB memory storage.

3:- Transfer Android 5.1.1 CyanogenMod 12.1 ROM .zip file that you’ve already downloaded from the above link, to the root folder of your SD card on the phone.

4:- Disconnect the Galaxy S2 I9100 from the PC and power it OFF in order to boot into Recovery Mode.

5:- Power ON the device while pressing and holding Volume Up + Home + Power buttons at the same time to enter into Recovery Mode.

6:- While your device is now in CWM Recovery, perform wipe data/factory reset, wipe cache partition and wipe dalvik cache also by navigating to Advanced > Wipe Dalvik Cache.

Note:- wipe dalvik cache will help you to prevent boot loops and other errors while ROM installation.

7:- Go back to the main Recovery Menu and choose install zip from SD card → choose zip from sdcard.

8:- Navigate to the CM12.1 Android 5.1.1 Lollipop custom ROM .zip file which you’ve already transferred to the SD card of your device previously. Select the ROM .zip file using the Power button and confirm the installation to begin.

9:- Go to +++++Go Back+++++ once the installation is completed. From Recovery Menu, reboot your device by selecting reboot system now.

Your Galaxy S2 will be rebooted and may take about 4 to 5 minutes to boot for the first time after installation.

Done! You’ve successfully updated Galaxy S2 I9100 to the latest Android 5.1.1 Lollipop with CyanogenMod 12.1 ROM.

Let us know in the comments area below if you have any query or trouble while installing this CM12.1 custom firmware featuring Android 5.1.1 Lollipop on your Galaxy S2.

Aamir Jamal

An Android Geek and audiophile who love to read and write reviews/tutorials about gadgets and new tech stuff. He has written 1007 guides and other posts.

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  1. Thank you! I understand what I am supposed to do, but get stuck on the way, since I cannot install the cm 12.1 zip file …
    What version of CWM recovery did you use and how can I get it?
    Thanks in advance!

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