Pros:
Cons:
Updating from the stock Android 4.1.2 to a custom Android 5.1.1 firmware offers several advantages:
Cause: Your EFS partition corrupted during flash.
Fix: This is serious. You must restore your EFS backup (which you hopefully made before this process). Always back up /efs using TWRP.
After the phone boots up (this may take longer than usual the first time), it is recommended to wipe the cache partition to prevent bugs.
Yes, with caveats. Installing Android 5.1.1 on your GT-I9100 via a custom ROM will not make it a 2023 flagship. The phone will still lag with heavy apps like Facebook or modern 3D games. However, for basic tasks (calls, SMS, light web browsing, music, YouTube at 480p), the gti9100 firmware 5.1.1 breathes essential life into an otherwise obsolete device.
If you are looking for even better performance and modern app support, consider Android 7.1 (Nougat) or Android 9 (Pie) builds for the I9100, but they are less stable. For a balance of stability and app support, 5.1.1 remains the best "final" firmware for the Galaxy S II.
Disclaimer: Modifying your device's firmware voids any remaining warranty (none for this device anyway) and carries a risk of bricking your phone. The author and sources mentioned are not responsible for any damage to your device. Proceed at your own risk. Always verify checksums (MD5) of downloaded files to ensure integrity.
Go to product viewer dialog for this item. , famously known as the Samsung Galaxy S2 Go to product viewer dialog for this item.
, officially peaked at Android 4.1.2 Jelly Bean. However, the developer community famously extended its life, allowing users to "update" the device to Android 5.1.1 Lollipop via custom ROMs like CyanogenMod 12.1. The Resurrection of a Legend: and Android 5.1.1 While Samsung stopped official support years ago, the
remains one of the most iconic devices in Android history due to its incredible third-party developer support. Moving from the aging Jelly Bean interface to the Material Design of Android 5.1.1 Lollipop transforms the device, offering a modern look and better app compatibility. Prerequisites for the Update
Before attempting to download and install a 5.1.1 firmware package, ensure your device meets these requirements: Model Check : This is strictly for the gti9100 firmware 511 download upd
(Exynos). Do not use these files for the I9100G or carrier-specific variants (like the SGH-T989). Root & Recovery : You must have a custom recovery installed, such as ClockworkMod (CWM)
: Ensure at least 60% charge to prevent a shutdown during the flashing process.
: Perform a full "Nandroid" backup in recovery mode. Flashing a new ROM will wipe all system data. Where to Download Firmware Files
Since there is no "official" 5.1.1 firmware from Samsung, you will need two specific ZIP files: Custom ROM (CyanogenMod 12.1 / LineageOS 12.1)
: These are the most stable builds for Android 5.1.1 on this hardware. Reliable mirrors can often be found on XDA Developers or archived ROM repositories. GApps (Google Apps)
: Because custom ROMs are "de-Googled," you need a GApps package (ARM, Android 5.1, Pico or Nano version) to get the Play Store back. Step-by-Step Installation Guide Transfer Files
: Move the downloaded ROM and GApps ZIP files to your phone's internal storage or SD card. Boot to Recovery : Power off, then hold Volume Up + Home + Power until the recovery screen appears.
: Select "Wipe" and perform a Factory Reset (Wipe Data, Cache, and Dalvik/ART Cache).
: Select "Install," locate the ROM ZIP file, and swipe to confirm. Flash GApps
: Immediately after the ROM is finished, repeat the "Install" process for the GApps ZIP.
: Select "Reboot System." The first boot can take up to 10 minutes as the system initializes. Still Matters Cons: Updating from the stock Android 4
The Samsung Galaxy S2 (GT-I9100) Go to product viewer dialog for this item.
never received an official Android 5.1.1 (Lollipop) update from Samsung; its official support ended with Android 4.1.2. To get 5.1.1, you must use a Custom ROM like CyanogenMod 12.1 or Resurrection Remix. 1. Preparation & Requirements
Backup: Backup all data, as this process will wipe your phone. Drivers: Install Samsung USB Drivers on your PC.
Recovery: You must have a custom recovery like TWRP installed. Due to the age of the device, you may need a "kernel with TWRP" to handle the newer Android file systems. 2. Download Necessary Files
You will need three specific files moved to your phone's internal storage or SD card: Custom ROM: Search XDA Developers for " Android 5.1.1 ROM" (e.g., CyanogenMod 12.1).
GApps: Download the "Pico" or "Nano" package for Android 5.1 (ARM) from OpenGApps.
Pit File (Optional but Recommended): Android 5.1.1 often requires more system space than the stock partition provides. Many users use a "Pit file" via Odin to repartition the internal storage. 3. Installation Steps
Boot into Recovery: Turn off the phone, then hold Volume Up + Home + Power.
Wipe Data: Select Wipe > Advanced Wipe and check Dalvik, System, Data, and Cache.
Install ROM: Go to Install, select your downloaded 5.1.1 ROM .zip file, and swipe to confirm.
Install GApps: After the ROM finishes, go back to Install and select the GApps .zip. Yes, with caveats
Reboot: Select Reboot System. The first boot may take 5–10 minutes. Critical Safety Warning
Official firmware for the Samsung Galaxy S II (GT-I9100) only reached Android 4.1.2 Jelly Bean Android 5.1.1 Lollipop , you must use unofficial custom ROMs like CyanogenMod 12.1 Download Sources
Since official support ended years ago, you will need to find archived files on developer community sites: Custom ROMs (Android 5.1.1): XDA Developers forum for i9100
for stable builds of LineageOS (formerly CyanogenMod) or Resurrection Remix. Google Apps (GApps): You must download a separate GApps package for Android 5.1 to have the Play Store and Google services. Official Stock Firmware:
If you need to revert to the original software (v4.1.2), sites like host original ROM files. Installation Overview
Updating to Android 5.1.1 is a manual process that typically involves these steps: Root & Recovery: Ensure your device is rooted and has a custom recovery like ClockworkMod (CWM) installed. Back up all data and specifically your EFS partition to avoid losing your IMEI/network connectivity. Wipe Device: Boot into recovery and perform a (Wipe Data/Factory Reset, Cache, and Dalvik Cache). Flash Files: Use the "Install zip from SD card" option to flash the first, followed immediately by the The first boot can take up to 10 minutes. Reflective Paper: The Longevity of the Galaxy S II
The "Legendary" S II: A Case Study in Community-Driven Device Longevity Samsung Galaxy S II (GT-I9100)
, released in 2011, represents a unique anomaly in the planned obsolescence of consumer electronics. While its official manufacturer support ended with Android 4.1.2, the device remains a "legend" in the developer community
If you still want to flash this stock ROM:
First boot will take 5–10 minutes. Be patient.
Cause: The ROM is checking your device model and fails.
Fix: In TWRP, go to Mount and uncheck System. Or, update to the latest TWRP version for I9100.