Xiaomi smartphone owners often face the desire to get rid of intrusive advertising and redundant code, which carries the shell MIUI. Model Redmi Note 9S, based on the powerful Snapdragon 720G processor, is an ideal candidate for transition to a clean operating system, which allows you to significantly speed up the interface and extend battery life.
The process of replacing standard firmware with custom requires care and follow the instructions accurately, since any errors can lead to the failure of the device. In this article, we will consider the full cycle of work: from unlocking the bootloader to the final configuration of GSI or specialized assemblies LineageOS.
The result of this manipulation will be a gadget that works as quickly and stably as possible, without system debris. It is critical to understand that unlocking the bootloader automatically voids the manufacturer's warranty if it still applies to your device.
⚠️ Attention: All actions you take are at your own risk. Mistaking steps can turn your smartphone into a brick.
Preparation of equipment and software
Before you start modifying system files, you need to prepare the workspace and download all the necessary tools. You will need a computer running the Windows operating system, since most utilities from Xiaomi do not support macOS or Linux in normal mode.
It will also require quality USB-cable, preferably original, to eliminate connection breaks at a critical time of data recording. ADB and Fastboot, which provide communication between the PC and the smartphone in service modes.
☑️ Checklist of preparations
Remember to make a full backup of all important data, as the process of unlocking and installing a new system involves completely removing information from the internal drive.
Unlocking the Bootloader bootloader
The first and most difficult step is to obtain permission to change the system partition through unlocking Bootloader, which requires you to link your Mi Account account in your phone settings and apply through the official Mi Unlock app.
After submitting an application, the system will require you to wait a certain period of time, which is usually from 7 to 168 hours, during which time you can not log out of your account on the device or reset your settings, otherwise the waiting timer will have to start again.
- 📱 Enable the developer mode by clicking 7 times on the build number in the About Phone section».
- 🔗 In the “Developers” menu, select “Mi Unlock Status” and link your account.
- ⏳ Wait for SMS notification of permission to unlock.
- 🔓 Launch the Mi Unlock utility on your PC, log in to the same account and put your phone into Fastboot mode (clamping down the power and volume buttons).
When the timer expires, reconnect in Fastboot mode and press the Unlock button in the program. The process takes a few minutes, after which the phone automatically restarts and clears all data.
What if the timer is off?
Installation of custom TWRP Recovery
The standard recovery menu does not allow installing third-party firmware, so you need to replace it with TWRP (Team Win Recovery Project). For the Redmi Note 9S model (codename curtana), you need to download the current image of img from a proven resource, for example, from the official developer site or the XDA Developers forum.
Place the downloaded file in the ADB tool folder on your computer and rename it to recovery.img for convenience. Open the command prompt in this folder and connect the phone in Fastboot mode.
fastboot flash recovery recovery.imgAfter successful recording, do not boot into the system immediately, as standard firmware can overwrite Recovery. You must immediately pinch the combination of power and volume buttons up to enter the installed TWRP menu.
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If TWRP asks for a password, enter the one you used to lock the screen before unlocking the bootloader. If the password doesn't fit, you may need to format the data.
Cleaning Partitions and Formatting Data
Before installing a new operating system, you need to completely clean old partitions to avoid file conflicts and errors. In the TWRP menu, go to the Wipe section and select Advanced Wipe.
Check the Dalvik/ART Cache, System, Vendor, and Data sections. Don't touch the Internal Storage section if you plan to take firmware files from your phone's internal memory, but for the complete purity of the experiment, download images through ADB Sideload.
Pay special attention to the Data section: it must not just be cleaned (Wipe), but formatted (Format Data), by entering the word yes. This action will remove the encryption left over from the old system, and allow the new firmware to work correctly.
| Section | Action. | Purpose |
|---|---|---|
| Dalvik / ART | Wipe | Cleaning up the app cache |
| System | Wipe | Removal of the old OS |
| Data | Format | Decryption of encryption |
| Cache | Wipe | Clearing temporary files |
Selection and installation of firmware
There are two main ways to get the Redmi Note 9S: installing a full custom firmware (like LineageOS, Pixel Experience) or using GSI (Generic System Image), which is optimized specifically for your phone’s hardware and is more stable.
Download the selected firmware zip archive and, if necessary, Google Apps (GApps) package if they are not built into the system. Throw files into the phone's internal memory or connect the flash drive through the device. OTG-adapter.
In the TWRP menu, click Install, select the firmware archive, and confirm the swipe installation. Once the process is complete, if the GApps are not built in, install them in the second step without rebooting.
⚠️ Attention: When installed GSI-Make sure you choose the version with the right partition type (A/B or A-only) and file system type (Ext4 Dynamic or otherwise the phone will not boot.
First start and initial setup
After successfully installing all components, press the Reboot System button.The first run can take anywhere from 3 to 10 minutes as the system compiles the app cache and adjusts the drivers.Don't panic if the screen goes out or the Android logo appears.
Go through the standard setup procedure: select a language, connect to Wi-Fi, and log in to a Google account. Pure Android will offer a minimal set of settings, which is its main advantage over congested interfaces.
It is recommended to immediately check the operation of the main modules: camera, microphone, speaker and fingerprint sensor. On custom firmware, camera drivers can differ from stock, so the quality of the photo is worth assessing first.
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The first launch of the new system is a critical moment: if the phone has gone into a cyclic bootloop, you need to go back to TWRP and perform a full reset (Format Data) again.
Possible problems and solutions
In the process of operation, there may be specific errors that are characteristic of informal assemblies, for example, sometimes VoLTE function does not work or the battery quickly discharges due to improper operation of the modem.
To solve communication problems, it is often helpful to flash the modem from the stock version of MIUI or install patches through Magisk. If the phone has stopped responding to commands, try entering EDL (Emergency Download Mode) mode to recover through service software.
- 🔋 Quick discharge: check battery stats in settings, maybe the background app calls "wakelock».
- 📷 Blurred photo: Try installing GCam (Google Camera) with the right config for your sensor.
- 📶 No network: make sure you select the right region and network type in the engineering menu.
The developer community is constantly updating firmware, so keep an eye on the threads on the forums to get security fixes and bugs. Regular system updates are key to stable operation of the modified smartphone.