Rollback from Android 9 to Android 8: safe downgrade without data loss

Updating to Android 9 Pie does not always live up to expectations: some users encounter slowdownapplication incompatibility or an inconvenient interface. Return to Android 8 Oreo technically possible, but the process requires preparation and understanding of the risks. Unlike standard updates, downgrading is an irreversible procedure that can lead to data loss, blocking of the device or voiding the warranty.

This instruction is suitable for most smartphones on Qualcomm Snapdragon (for example, Samsung Galaxy S8/S9, Xiaomi Redmi Note 5/6, OnePlus 5/6), but not universal. Devices on Mediatek or Exynos may require other tools. Before you start, check whether your model supports official rollback via Fastboot or ODIN.

⚠️ Attention: Manufacturers often block the ability to downgrade via anti-rollback (rollback protection). On Huawei, Honor and some models Xiaomi after 2019 this may lead to a “brick” (inoperable device). Check the risks for your model on the forums 4PDA or XDA-Developers.

1. Preparing your device: backing up and unlocking

The first step is to save all important data. Downgrade erases the device's internal memory, including photos, contacts and messages. Use cloud services or physical copying on a PC:

• 📱 Contacts and calendar: sync with Google Account (Settings → Accounts → Google).
• 📷 Photo/video: copy to your computer or download to Google Photos.
• 💬 Messages: use applications like SMS Backup & Restore.
• 🎮 Applications: export the list via Titanium Backup (root access required).

Next unlock bootloader. This step is required to install custom firmware. On most devices, unlocking erases data, so make it after backup. Instructions vary:

• 🔓 Samsung: enable OEM Unlock in Settings → For developers, then use ODIN.
• 🔓 Xiaomi: get permission via Mi Unlock Tool (may take up to 720 hours of waiting).
• 🔓 Google Pixel: run command fastboot flashing unlock.

⚠️ Attention: Unlock bootloader on some models (for example Sony Xperia or LG) may result in loss of DRM features (for example Widevine L1 for Netflix in HD). Check the consequences for your model!

2. Choice of firmware: official vs custom The first option is preferable, but is not always available.

Suitable for downgrade: either official firmware from the manufacturer, or custom (For example, LineageOS). The first option is preferable, but is not always available.

For official firmware, use proprietary utilities:

• 📱 Samsung: app ODIN (version 3.14+).
• 📱 Xiaomi: Mi Flash Tool (choose mode clean all).
• 📱 Google Pixel: factory images from the site Google.

⚠️ Attention: Firmware for Android One (for example, Nokia or Motorola) often contain rollback protection. An attempt to install an old version may lead to an error. ERROR: anti-rollback check fail.

Download the correct firmware version for your model|

Checking the checksum (MD5) of the file|

Battery charge > 50%|

Drivers installed ADB/Fastboot on PC|

Antiviruses are disabled (can block ODIN/Mi Flash)-->

3. Unlocking the bootloader: step-by-step guide

The unlocking process is different for each brand. Let's consider the universal method through Fastboot (for devices with Qualcomm):

1. Activate Developer mode 7 times: go to Settings → About phone and click on Build number.
2. Enable USB debugging i OEM unlocking in Settings → For developers.
3. Connect your phone to the PC and run the commands:

   adb reboot bootloader
   fastboot flashing unlock

4. Confirm unlocking on the device screen (volume buttons).

For Samsung use ODIN:

1. Download Odin3_v3.14.zip and unpack.
2. Boot the phone into mode Download Mode (turn off, then hold Bixby + Volume down + Power).
3. Connect to the PC, in ODIN select the firmware file in the field AP and click Start.

⚠️ Attention: On devices Huawei after 2018, unlocking the bootloader requires a unique code that is no longer officially issued. - exploiting vulnerabilities (for example, DC-Unlocker), but this is risky.

4. Installing the firmware: Fastboot vs Recovery

The installation method depends on the type of firmware. Fastboot or proprietary utilities, for custom ones - TWRP.

Method 1: Fastboot (for official firmware)

1. Unpack the firmware (for example, factory-image-*.zip for Pixel).
2. Connect the phone in mode Fastboot and do:

   fastboot flash boot boot.img
   fastboot flash system system.img
   fastboot flash vendor vendor.img
   fastboot reboot

Method 2: TWRP (for custom firmware)

1. Install TWRP Recovery via Fastboot:

   fastboot flash recovery twrp-3.6.0.img

2. Boot into TWRP (press Volume up + Power).
3. Do Wipe → Advanced Wipe (check Dalvik, Cache, System, Data).
4. Install the firmware ZIP archive via Install.

⚠️ Attention: On some devices (for example, OnePlus 6/6T) after installing custom firmware stops working VoLTE i Wi-Fi Calling. The solution is a patch Modem Firmware via Magisk.

1. Repeat the installation with complete Wipe.

2. Flash the kernel (boot.img) separately.

3. Check the compatibility of the version TWRP with your firmware.-->

5. Solving common errors

Downgrade rarely goes smoothly. Here are typical problems and ways to fix them:

fastboot --disable-verity --disable-verification flash vbmeta vbmeta.img

If after a rollback it stops working Google Appsinstall the package Open GApps (choose the version for Android 8.1 i architecture ARM/ARM64). To do this:

1. Download open_gapps-arm64-8.1-pico-*.zip.
2. Install via TWRP after the main firmware.
3. Run Wipe → Dalvik/Cache.

6. Data recovery and final setup

After a successful rollback:

1. Restore the data from a backup copy (except for system applications - they may be incompatible).
2. Update applications via Google Playbut avoid versions that require Android 9+.
3. Check basic functions:
   • 📞 Calls and mobile data (set up APN manually if necessary).
   • 📶 Wi-Fi and Bluetooth.
   • 🔋 Charging and battery recognition.

To avoid automatic updates to Android 9 in the future:

• 🚫 Turn off automatic updates in Settings → System → Update Software.
• 🛡️ Install Magisk and module Disable Force Encryption (if the firmware encrypts /data).
• 🔧 Use ADBto block the update package:

  adb shell pm disable-user --user 0 com.android.updater

⚠️ Attention: On some devices (for example, Samsung Galaxy S9) after downgrading it may stop working Samsung Pay due to changes in versions. Knox. There is no solution - this is a security limitation.

7. Alternatives to downgrade: optimizing Android 9

If the purpose of the rollback is to improve performance, try optimizing first Android 9:

• 🔄 Reset the settings to factory settings (Settings → System → Reset).
• 🗑️ Disable unnecessary system applications via ADB:

  adb shell pm uninstall --user 0 com.sec.android.app.launcher

• ⚡ Install a lightweight launcher (for example, Nova Launcher) and disable animations in Settings → For Developers.
• 🛠️ Use Magisk to remove bloatware (module Universal Debloater).

For devices with Project Treble (for example, Xiaomi Mi A2) you can install Generic System Image (GSI) on database Android 8 without loss of functionality. Instructions:

1. Download phhusson’s GSI for ARM64.
2. Flash through Fastboot:

   fastboot erase system
   fastboot flash system system.img

3. Install vbmeta with disabled check:

   fastboot --disable-verity --disable-verification flash vbmeta vbmeta.img

FAQ: Frequently asked questions about downgrading