[ROM][I9100G][CM12.1] CyanogenMod 12.1 [UNOFFICIAL][Android 5.1.1][20161120][CM 12.1]


Senior Member
Apr 10, 2014
[ROM][I9100G][5.1.1] Cyanogenmod 12.1 [UNOFFICIAL][CM12.1][Galaxy S2G][CM 12.1]

CyanogenMod is a free, community built, aftermarket firmware distribution of Android 5.1.1 Lollipop, which is designed to increase performance and reliability over stock Android for your device.

This is an UNOFFICIAL build of Cyanogenmod CM 12.1 for Samsung Galaxy S2 G (I9100G). It's build completely from sources on github.com/cyanogenmod & xdaamg. Standard functionalities are working. It's good for daily use. Android 5.1.1 is running smooth on this device.

By flashing a custom rom, your warranty is void.
I am not responsible for bricked devices, dead SD cards and so on. You are choosing to make these modifications.
I will not give support for modifications and apps you install/flash.
Confirmations of working things are welcome. If you found a bug, provide a logcat of it.
Note: CM13/Android 6.0.1 is available for i9100g now. Please read working/not working section before you upgrade to CM13. CM12.1 is the recommended version.

First time installation instructions:
  • Download I9100G CM-12.1 ROM to your sdcard
  • Download Google Apps to your sdcard (optional). Recommended: OpenGApps (20150821)
  • Backup your media files (photo, music, downloads) stored on internal storage (optional)
  • Flash TWRP Recovery TAR with Odin when you use Stock Rom. When you are using CWM Recovery/Blazing Kernel/TWRP IsoRec or an other version of TWRP, flash TWRP Recovery only.
  • Reboot into recovery (switch off, then hold power & home & volume-up, release power when you see samsung logo)
  • Wipe data (system, data, cache, dalvik)
  • Install ROM CM-12.1-2-i9100g.zip from sdcard
  • Install Google Apps from sdcard (optional)
  • Reboot System and wait, first boot will take some minutes. Google App and Play Store will be updated automatically, when you start Play Store, wait until it's finished, before you try to install apps.

Updating ROM:
  • Download I9100G CM-12.1 ROM to your phone/sdcard
  • Boot into recovery
  • Install ROM CM-12.1-i9100g
  • Wipe Cache/Dalvik
  • Reboot System

Download I9100G CM12.1 ROM UNOFFICIAL:
Download i9100g CM12.1 20161120

Support development of this rom:
If you find this rom useful, consider donating please. Your donation is used to cover costs for build computer/energy and a part of time consumption. Your donation helps to keep this rom alive!

Download G-Apps:
Download Open GApps (20150821) (recommended for first time installation). Alternative Download for OpenGApps 5.1 Nano 20150821.
Visit opengapps.org to download latest gapps (usually not needed). When everything works fine, i recommend not to touch your gapps.

Alternative Gapps which may also work:
Download PA-GApps 5.1 Nano 201504. Alternative Download PA-GApps 5.1 Nano 201504.

Android-Version: 5.1.1 (R37)
CyanogenMod-Version: 12.1
Security patch level: 01.11.2016
Kernel-Version: 3.0.31
SELinux-Status: Strikt

Standard functionalities are working. No known major errors or force closes. It's good for daily use.
Tested functions: Telefon, sms, wifi, data 2g/3g, camera, 3d-grafics, sensors, gps, compass, vpn, wifi hotspot, screencast, speaker, playstore.

Special features:
  • TWRP IsoRec: Booting TWRP from recovery partition
  • F2FS: Flash-friendly file system supported (sdcard, internal, cache)
  • Good standby times
  • Responsive, smooth gui
  • Last i9100g cm-12.1 rom which still gets updates (official cm-11.0 builds for i9100g ended 08/2016)

Changelog CyanogenMod:
CM12.1 changes

  • Root: To enable root access, activate developer options and go to settings>developer options>root access and set it to 'apps only' or 'apps and adb'.
  • Recovery: Cyanogenmod 12.1 comes with Cyanogen Recovery by default. But this rom supports booting isorec twrp recovery. Flash twrp isorec recovery to recovery partition. Rom will use then twrp as prefered recovery and ignore default recovery. Follow flash instructions for i9100g isorec twrp recovery to install twrp isorec recovery. If your recovery is not working, enter 'download mode' and flash a new recovery via odin, for example TWRP
  • GApps: If you have problems flashing gapps or force closing google play services, do a clean flash and use recommended Open GApps 20150821 or pa-gapps for android 5.1 from download link above.
  • Audio/Video synchronisation: Update to latest build and deactivate AudioFX when you experience audio not in sync with video

  • Low app space: If you are low on app data storage, think about repartitioning your phone storage. 4 to 6 gb should be sufficient even for many apps. Follow instructions in this thread. Alternatively use Lanchon Repit Tool.
  • Battery: Display and data connections/syncing use most energy. I suggest to reduce display brightness to a minimum and switch off adaptive brightness. Also switch off background data connections/syncing for apps you don't use or which will be updated when you really use it.
  • After first flash give phone some extra time to complete all tasks, even when it's reacting already to your inputs, it's working hard. Wait some minutes. It's also a good idea to do another reboot after some time. This solved some problems in the past.
  • Force closes: If you are experiencing force closes try first to clean cache/dalvik cache with recovery. If it's still not working, go to settings/apps, find the offending app and clear data. Still not the solution? Then do a clean flash with factory reset.

Known (minor) problems:
  • Activating flashlight with quicksetting-icon (-> use another flashlight app and (optionally) replace lockscreen app for quick access). Or upgrade to cm13.
  • Manual selection of phone network -> use automatic network selection

Changelog bugfixes:
  • 20150825: high cpu usage caused by 'system_server' process fixed
  • 20150826: home button fixed
  • 20150826: Auto rotation fixed
  • 20151108: Wifi Hotspot fixed
  • 20151115: Touchkey light fixed
  • 20151115: VPN fixed
  • 20161112: 'Dirty Cow' kernel security fix, Video/Audio synchronisation improvements, Screencast fix
  • 20161120: Security fixes: Android security patch level 01.11.2016

TWRP Recovery only:
Download TWRP Recovery only signed
Download TWRP Recovery only signed
Download TWRP Recovery only signed TAR for Odin

CM12.1 ROM archive (outdated, but it could help if latest rom is not working):

XDA:DevDB Information
I9100G CyanogenMod CM 12.1 Android 5.1.1, ROM for the Samsung Galaxy S II

Source Code: http://www.github.com/CyanogenMod

ROM OS Version: 5.1.x Lollipop
ROM Kernel: Linux 3.0.x
Based On: CyanogenMod

Version Information
Status: Beta
Current Beta Version: 20161120
Beta Release Date: 2016-11-20

Created 2015-08-24
Last Updated 2017-06-20


Last edited:


Senior Member
Dec 22, 2012
for what it have a lof of bugs

Known problems/errors:
- home button not working as expected
- High cpu usage/battery drain caused by 'system_server' process
Did not find a reason for it. It's not active all the time. Sometimes, when it's inactive, telefon goes to deep sleep and all is normal. But when it's active, cpu state is at 1,2 GHz for long, long time, without stop. Who can debug/analyze this process or provide information how to fix it?

cpu state is at 1,2 GHz for long, long time, =not battery friendly
  • Like
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Senior Member
May 5, 2011
Download was updated to 20150824:
- home button setting changed (working now?)
- selinux settings changed
*home button not working still
* screen rotate not working
* cpu always work 1.2ghz this is more battery used
otherwise fast and looking good.
Last edited:
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Senior Member
Apr 10, 2014
I changed keylayout and home-button is working now. Wakeup, close apps, app history. Thank you, Diatomix for this useful hint!

Auto-rotation is also working now.

Build of new ROM is in progress. I will upload it in some minutes.
  • Like
Reactions: ze7zez


Senior Member
May 5, 2011
I changed keylayout and home-button is working now. Wakeup, close apps, app history. Thank you, Diatomix for this useful hint!

Auto-rotation is also working now.

Build of new ROM is in progress. I will upload it in some minutes.
cpu used 1,2 ghz or fixed this?


Senior Member
May 5, 2011