How to unlock and relock Android bootloader with fastboot

[Development] How to unlock and relock Android bootloader with fastboot

hovatek
Administrator

49,597

26-07-2017, 02:47 PM

#1

This guide will explain how to unlock and relock the bootloader of an Android device using fastboot. Except for rare cases like Motorola devices, your bootloader must be unlocked to flash even factory files via fastboot. While you can flash modified files (TWRP/GSI/Custom ROMs) to your Mediatek (MTK), Spreadtrum (SPD) or Qualcomm (QLM) Android devices using their flash tools on a locked bootloader, doing so is just asking for a boot loop or bricked device.

It is important to mention that this is a generic approach and doesn't work for all devices. Some relevant guides on bootloader unlock to checkout include:

Requirements

Setup ADB-Fastboot on your PC. For Spreadtrum devices, follow this guide (in order to enable adb detect your device)
Enable USB Debugging and OEM Unlocking (if available)

How to unlock Android bootloader using fastboot

Follow the steps below to unlock the Bootloader of an Android device

See the video tutorial below or @ https://youtu.be/DL5NMR-n4_Q

Open the adb folder
Hold Shift (on the keyboard) then right-click on a blank space in the folder > Select Open Command window here
Command prompt screen (ADB) should now be open
Connect the device to the PC (via USB cord) while ON then run the command below (by "run", I mean type then press Enter

Code:

adb devices
If you've set up everything right, the device should get detected under the List of devices attached
Run the command below to get the device into Bootloader (fastboot)

Code:

adb reboot-bootloader

if that fails

Code:

adb shell reboot fastboot
The device should now boot into fastboot (a black or coloured screen with the text fastboot)
In fastboot, test detection/connection to the device using the command:

Code:

fastboot devices
If fastboot is set up right, you should see its ID printed out
Now, check the device's Bootloader lock status using either of the two commands below (if it's locked or unlocked)

Code:

fastboot oem device-info fastboot getvar unlocked
1. If you use the fastboot oem device-info command and the result is false then your bootloader is locked but if the result is true then the bootloader is unlocked
2. If you use the fastboot getvar unlocked command and the result is no then your bootloader is locked but if the result is yes then the bootloader is unlocked
If you've confirmed your bootloader is locked, then run the command below to unlock the Bootloader

Code:

fastboot oem unlock
If that doesn't work then try the commands below:

Code:

fastboot oem unlock-go fastboot flashing unlock fastboot flash unlocking fastboot bbk unlock_vivo

Note: Vivo phones require a custom fastboot binary (attached at the end of this post)
Some devices require you to also run:

Code:

fastboot flashing unlock_critical
You should get a prompt (on the device) asking you to press Volume up to confirm or Volume down to cancel. Press Volume up on the device (for some phones it is actually the opposite; Volume down would confirm while up would cancel or do nothing)
Once the Bootloader is unlocked, reboot the device using

Code:

fastboot reboot
The device might take a while to boot up (since it is a first boot) so be patient

How to relock Android bootloader using fastboot

It is important to return the device to stock ROM by flashing its factory/stock/official firmware before relocking the bootloader. Relocking the bootloader with a custom partition (TWRP/Custom ROM/GSI) still in place will brick the device.
Depending on the unlock command you used, try its corresponding bootloader relock command:

Code:

fastboot oem lock

fastboot oem lock-go

fastboot flashing lock

fastboot flash locking

fastboot bbk lock_vivo

Important Notice

This guide isn't guaranteed to work on all (Mediatek, Spreadtrum, Qualcomm, Exynos, Hisilicon, Intel etc) Android devices
Ensure to backup your important stuff because unlocking your Bootloader wipes your data (/userdata)
Unlocking the bootloader bricks some devices so ensure to relock or flash the firmware if you find yourself in such a situation
If you successfully installed ADB / fastboot and your device still isn't detected then it is most likely due to old ADB or drivers, fix it using the guide on fixing ADB and fastboot detection problems

This post was last modified: 17-11-2023, 12:25 PM by hovatek.

Attached Files

vivo_fastboot_for_windows.zip
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How to unlock Android bootloader using fastboot

How to relock Android bootloader using fastboot

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