How to flash Xiaomi Redmi Note 9: all the ways from the official MIUI to custom builds

The Xiaomi Redmi Note 9 remains one of the most popular budget smartphones even years after its release. But over time, standard firmware begins to slow down and updates from the manufacturer stop coming out, in which cases, flashing the device can restore its previous speed, add new features or even install the current version of Android.

In this guide, we will analyze all the current ways to implement the Redmi Note 9 firmware (codenamed merlin): from official updates through MIUI Updater to install custom reveria and alternative firmware like LineageOS or Pixel Experience.

Important: The firmware procedure for the Redmi Note 9 Pro (joyeuse code) and Redmi Note 9S (curtana code) has key differences! Make sure your model matches merlin exactly (check in Settings → About Phone → Model).

1. Firmware Preparation: What to Do Before Starting

The first step is to back up data, and firmware, especially through fastboot or customized recycles, erases all user files (photos, contacts, messages).

• 📱 Mi Cloud – sync contacts, notes and photos (up to 5GB free).
• 💾 Local Copying – Transfer files to a PC or external drive.
• 🔄 Titanium Backup (requires root) – to save applications and their data.

Check the MIUI version and the status of the bootloader:

1. Open Settings → About your phone and write down the current version of MIUI (e.g. MIUI Global 12.5.3).
2. Type ##4636## in the dialer, select Phone Information, and check the Lock State line, if there's Locked, the bootloader is locked.

Record the IMEI of the phone (in Settings → About the phone → General information)

Check the battery power (minimum 60%)

Download Mi Flash Tool drivers for PC

Prepare. USB-cable (original, without damage)

Disable antivirus on PC (can block firmware files)

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Critical: If you plan to install custom firmware, unlocking the bootloader will reset all data on the phone, including internal memory (including photos on the phone). SD-This process is irreversible if it is used as an internal storage device!

2. Official methods of firmware: MIUI Updater and Mi Flash Tool

If your goal is to upgrade the Redmi Note 9 to the latest official MIUI without risk, use the built-in tools.This is the safest method, but it won’t allow you to install custom firmware or newer versions of Android than those that Xiaomi supports.

Update via MIUI Updater (OTA)

Suitable for installing fresh security patches or minor MIUI updates:

1. Go to Settings → About the phone → System update.
2. Click on the icon «⋮» (three dots) in the upper right corner and select Select Service Package.
3. If an update is available, download it (the file weight is usually 1.5-2.5 GB).
4. After downloading, click Reboot and Update.

Limitations of the method:

• ❌ It doesn't allow you to downgrade the version. MIUI (downgrade).
• ❌ It doesn’t work if the phone is unlocked or has custom recycled.
• ❌ Often gets stuck checking for updates due to Xiaomi server issues.

Firmware via Mi Flash Tool (fastboot)

This method will be useful if:

• 🔄 Restore the phone after a failure ("brick»).
• 📥 Install the full version MIUI (non-incremental update).
• 🔓 Unlock the bootloader (the first step for custom firmware).

Instructions:

1. Download the official firmware for Redmi Note 9 (merlin) in.tgz format (e.g, merlin_global_images_V12.5.3.0.RJOMIXM_20211012.0000.00_11.0_global_50a4d3a0b4.tgz).
2. Unclose the file and place the firmware folder in the root of the C:\ drive (the path should not contain Cyrillic!).
3. Install the Mi Flash Tool and Qualcomm drivers.
4. Turn off the phone, press Volume down + Power to enter Fastboot mode (a hare in a hat-eared hat will appear).
5. Connect your phone to your PC, in the Mi Flash Tool, select the firmware folder and press Refresh.
6. At the bottom, select Clean all (full clean) or Clean all and lock (clean + lock the bootloader) and press Flash.

Official MIUI (Stable)

Official MIUI (Developer)

Custom firmware (LineageOS, Pixel Experience, etc.)

I don't know, I need some advice.-->

Note: If you have a Mi Flash Tool error, you can't find it 'flash_all_lock.bat', So you downloaded the firmware for the locked bootloader, and your phone is already unlocked:

1. Download the firmware version marked unlocked.
2. Or manually delete files from the firmware folder flash_all_lock.bat and flash_all_except_storage_lock.bat, Just leave it. flash_all.bat.

3. Unlocking the bootloader: a mandatory step for custom firmware

Xiaomi locks the bootloader on all its devices to protect against unauthorized changes. To install TWRP, LineageOS or any other custom firmware, you first need to unlock the bootloader. This process takes at least 7 days (due to Xiaomi's policy) and requires:

• 📱 Mi Account Account Linked to Phone.
• 🔗 A stable Internet connection (better via Wi-Fi).
• 💻 Computer with drivers installed ADB/Fastboot.

Step-by-step:

1. Turn on the phone Developer Mode: go to Settings → About Phone and 7 times click on the MIUI version.
2. Return to Settings → More → For developers and activate: Debugging by USB Unlock OEM (an important item!)

Connect the phone to the PC, confirm the debugging permission.

Mi Unlock Tool

Mi Account

Loudness down + Nutrition

Fastboot

Mi Unlock Tool

Unlock

Attention: after unlocking the loader:

⚠️ The phone will perform a complete reset to factory settings, including deleting all data in internal memory (including photos on the phone). SD-The card, if used as an extension of internal storage, will also disable Find Device and Mi Cloud before re-authorizing.

4. Installation of the TWRP custom recovery

TWRP (Team Win Recovery Project) is an alternative reclaimer that allows custom firmware, backups and system repair. For Redmi Note 9 (merlin), use informal builds, as there is no official support.

Installation instructions:

1. Download the current version TWRP for merlin from the forum XDA Developers (e.g., developers, twrp-3.7.0_11-merlin-mauronofrio.img).
2. Place the file in a folder with ADB/Fastboot on your PC (e.g., C:\platform-tools\).
3. Turn off the phone, press Volume Down + Power to log into the Fastboot.
4. Connect your phone to your PC and execute the command: fastboot flash recovery twrp-3.7.0_11-merlin-mauronofrio.img
5. Without turning off the cable, do it immediately: fastboot boot. twrp-3.7.0_11-merlin-mauronofrio.img It'll load the phone into TWRP without rewriting the image standard recycle.

fastboot flash recovery twrp.img


fastboot reboot recovery

This will make the phone boot up in TWRP, where Disable_Dm-Verity and avoid recycled.

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5. Install custom firmware: LineageOS, Pixel Experience and others

Custom firmware allows you to upgrade the Redmi Note 9 to new versions of Android (like Android 13), remove unnecessary Xiaomi apps and improve performance. Popular options for merlin:

Instructions for installation (on the example of LineageOS):

1. Download firmware (e.g. lineage-20.0-20230601-UNOFFICIAL-merlin.zip) and GApps (e.g. NikGApps for Android 13).
2. Transfer files to your phone or external SD-map.
3. Download to TWRP (see Section 4).
4. Run Wipe → Advanced Wipe and mark: Dalvik / ART Cache System Data Cache

Install → select the file

GApps

Disable_Dm-Verity_ForceEncrypt.zip

Reboot → System

Typical errors and decisions:

• 🔴 Error 7 when installed - mismatch of the device model.
• 🔴 Phone stuck on logo after firmware - not installed Disable_Dm-Verity. Come back in TWRP and pass it through.
• 🔴 No network after firmware – download and stitch separately firmware for your model (look for the XDA or 4PDA).

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6. Solving problems after firmware

Even with the exact following of the instructions, there may be problems.

Phone not switched on ("brick")

Symptoms:

• 🔳 Black screen, no response to buttons.
• 🔄 Download to Fastboot, but no further.
• 🔴 Red. LED-flasher.

Decisions:

• 🛠️ Soft brick (phone is defined in fastboot): sew the official MIUI Using the Mi Flash Tool (select Clean All).
• 💀 Hard brick (no reaction to fastboot): try to pinch Volume up + Loudness down + 20 seconds power (emergency restart) If it doesn't work, call the service center.

6.2. No network or mobile Internet

Causes and solutions:

• 📡 Incompatible modem: run firmware for your model (download from the XDA or 4PDA).
• 📶 Wrong settings APN: Go to Settings. → SIM-maps and mobile networks → Access points (APN) Add your operator’s settings manually.
• 🔄 Resetting network settings: Settings → System system → Resetting settings → Resetting network settings.

Fast battery discharge after firmware

A common problem after installing custom firmware.

• 🔋 Battery calibration: fully discharge your phone, then charge to 100% without interruption.
• 🛠️ Background Processes: In LineageOS or Pixel Experience, disable unnecessary Google services in Settings → Annexes → Google Play Services → Battery → Optimization.
• 🔄 Firmware core: Some custom cores (e.g. FrancoKernel) may conflict with the battery.

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7.How to get back the official MIUI after custom firmware

If custom firmware is unstable or you want to return the warranty, you can roll back to the official MIUI.

1. Download the official firmware for merlin in.tgz format.
2. Unclose it and put it in a folder. C:\platform-tools\.
3. Turn off the phone, press Volume Down + Power to log into the Fastboot.
4. Connect your phone to your PC and execute the command: fastboot flash boot.img fastboot flash recovery.img fastboot flash recovery system.img fastboot flash vendor vendor.img fastboot erase userdata fastboot reboot

Attention:

⚠️ If you block the bootloader after returning to the MIUI (With the fastboot oem lock command, the phone will perform a full reset and all data will be deleted without recovery, and this can lead to a “brick” if the firmware is not designed for a blocked bootloader.

Alternatively (via Mi Flash Tool):

1. In the Mi Flash Tool, select the official firmware downloaded.
2. At the bottom, select Clean all and lock (this will lock the bootloader and return the phone to factory status).
3. Press Flash and wait until it is completed (the process will take 5-10 minutes).

8. Frequently Asked Questions (FAQ)