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What Is Bootloader And How To Unlock Bootloader On Android Phones [Complete Guide]

If you are new to the world of Android hacking and rooting, then there are many geeky terms that might bamboozle you and might end you up with quitting the idea of rooting altogether. One such term that confused me too before I was trying to root my Nexus One long ago was “Bootloader”. I went through many online tutorials, hopped through infinity YouTube And Vimeo videos for a simple answer that why on earth I need to unlock my phone’s bootloader before trying to install any custom ROM or even attempting to root. Although I wasn’t able to acquire an answer at that time, but now as the time has changed and we have access to more refined information, the bootloader mystery puzzle has started to fall in place. So in this guide, we will be going through basic questions like what is a bootloader? Why you’d like to unlock it? and how to unlock? On our way, we will also see what threats a user faces when unlocking a bootloader.

nexus one BLWhat is a Bootloader?

In literal terms, bootloader is code that is executed before any Operating System starts to run. The concept of bootloaders is universal to virtually all Operating systems that inculcates operating systems on your PC, laptop, smartphones, and other such devices. Bootloaders basically package the instructions to boot operating system kernel and most of them also have their own debugging or modification environment. As the bootloader kicks off before any piece of software on your device, it makes it extremely processor specific and every motherboard has it’s own bootloader. This is one reason that all Android phones have different Custom ROMS developed due to high variance of processing hardware present on the device. The iDevices running iOS somewhat share the same hardware specs and hence you don’t see much variance in their bootloaders.

Android Bootloaders

Every Android phone has a bootloader that instructs the operating system kernel to boot normally. But you need to understand one thing here that as Android OS is an open source OS and is available on a variety of different hardware, every manufacturer has their own version of bootloader specific for the hardware present in it’s environment. We also saw couple of weeks back that Motorola packaged an “eFuse” command in their Android phones, which could brick (permanently turn off) your device in case you tried to flash a Custom ROM.

Why is Bootloader Locked?

A bootloader is usually locked on an Android device because although it’s an open source OS, still the manufacturers want you to stick to their Android OS version specifically designed for the device. In order to apply this concept, manufacturers lock the bootloader. With a locked bootloader on Android devices, it is virtually impossible to flash a Custom ROM and forced attempts void warranty as well as usually end up in bricks. Therefore, the first step is to always unlock the bootloader.

Why To Unlock Bootloader On Android Devices?

The explanation to this question is really simple. If you want root, you’d be wanting to flash Custom ROM post-root, and if you want to install a Custom ROM, you’d need to have your stock bootloader unlocked. In simple terms Unlocking the bootloader allows you to install custom Firmware on your Android phone.

Warning: Unlocking your phone’s bootloader voids its warranty. It also completely wipes (formats) your Android phone’s internal memory including applications, contacts, SMS and MMS messages etc.

How To Unlock Bootloader On Nexus Android Devices:

Before attempting this guide to unlock your bootloader, please note that this is intended for Android phone with STOCK ANDROID OS ONLY. We will be using a Google Nexus One as our reference because it comes with zero user interface alteration from it’s manufacturer. If you are looking to unlock bootloaders on handsets which already have a custom UI from manufacturers installed like HTC Sense, Samsung TouchWiz etc, then this guide won’t be applicable.

  1. The first step is download and install Android SDK as instructed in this post.
  2. Once you are done with downloading and installing SDK, turn off your device and boot in bootloader mode:
    • On Nexus One, press and hold the power button and trackball.
    • On Nexus S, press and hold the volume-up and power buttons.
    • On Galaxy Nexus, press and hold volume-up, volume-down and power buttons.
    • On Nexus 4, press and hold volume-down and power buttons.
    • On Nexus 7, press and hold volume-down and power buttons.
    • On Nexus 10, press and hold volume-up, volume-down and power buttons.
  3. Connect your device to your PC via USB and wait till any drivers are installed, which should happen automatically.
  4. Now go to command prompt / terminal interface on your computer and type following command:
    fastboot oem unlock
  5. Once this is done, your phone will show a screen that will prompt you regarding unlocking bootloader. Read through the instructions carefully and confirm by pressing volume up button followed by the power button.

There you go! You now have your bootloader on your Nexus Android device unlocked.

Picture Credit: CyberTrends
Thanks Modaco For Unlocking Instructions


  1. #1- i wanna root my android (alcatel)
    #2- for rooting bootloader should be unlocked? Isn’t
    #3- after unlocking bootloader everything wipes such as applications, mms, sms, userdata?
    I want the answer can anyone tell me please…

  2. Does this work for Alcatel OneTouch Fierce 2? Model 7040n

    Would appreciate help with custom recovery since there seems to be no guide for this phone. Thank you in advance.

  3. sir,…hot to make script unlocker bootloader for mediatek,or tool unlocker bootloader specially for mediate 64bit,..thanks

  4. How do i relock bootloader on my HTCdesire eye?
    Because i want to upgrade to android 6.0 and i can’t becouse it always sends me bootloader and i can’t open recovery mode

  5. Sir,

    Can the stock/custom firmware from firmware website links be flashed in Lava Pixel v1 without unlocking the bootloader?? Lava Pixel v1 has two pre-installed apks (Flipkart & Mynrtra) which can not be uninstalled even after normal system uninstaller (root) apps without unlocking the bootloader.

    I don’t know how to unlock Lava Pixel v1’s locked bootloader.

    Will unlocking need some special code or password??
    One last thing, it is absolutely esaential to flash IMEI number flashing in Lava Pixel v1 after the said stock firmware flashing???

    Please, respond.

  6. Hey guys , I have a i527 rooted , but from what I understand the bootloader is locked by hardware not filmware , it has to be sent back to at&t to be unlocked by a special box and cable , does anyone know if at&t will actually unlock it ? It’s getting to be an older device by now , or does anyone know of a work around ? Thanks.

  7. Hello,
    My Nexus 4 phone cannot be opened after updating android 4.3.
    Any suggestion to fix this problem?

  8. I know this is an old post, but the nexus 6 OS allows bootloader in the dev options with no extra downloads

  9. BootUnlocker for Nexus Devices app (Play Store) lets you unlock the bootloader without any wipes. Also, if you own a Oneplus One the warranty its not voided with the bootloader unlock 🙂

  10. Can anyone tell me if the Nook Simple Touch has a bootloader?

    And if it does, does it need to be unlocked?

    • of course it has a bootloader. it depends on you to modify your device or not. if wanna root your device and install custom roms, then you must unlock bootloader. there is another reason for unlocking bootloader, is to uninstall pre-installed apps what comes with your device. like google services, and other data and power and storage eating apps.

    • Well, I rooted a long time ago by modding my kernel and flashing it through ClockworkMod. However, I never did an “unlock the bootloader” step – which leads me to believe that my NST doesn’t acutally have one.


  11. “every motherboard has it’s own bootloader”

    I know this article was written ages ago, but just for-the-record, this statement is incorrect. You are confusing bootloader with motherboard firmware (commonly in the form of the BIOS with PC’s). Motherboard firmware and bootloaders are not the same thing. Firmware is stored in ROM (read only memory) on the board itself, while bootloaders are installed along with an operating system on non-volatile storage media (read: Hard Drives), and are unique to that operating system. They don’t really have anything to do with a motherboard’s BIOS/firmware.

    • 2 year ninja-edit: What you’re “unlocking” or disabling is the secureboot-like feature on the firmware, which controls what the motherboard’s firmware (and thus by extension the device) can boot to – such as custom ROMs. This might be construed as a very early stage bootloader, but it’s still not the same thing as a conventional bootloader proper seeing as how every OS still has its own bootloader.

  12. So I got here this Samsung Galaxy S2, which has trouble booting; it’s like the turn-on/-off button doesn’t work properly anymore. Battery is full. But the strange thing is, when I plug in the charger and I try to boot it, I get a Bootlader Unlock screen. I’ve looked the image up online but the images I find contain a “yes” and a “no” option, mine does not. I can’t do anything with it. Anyone any ideas about what’s going on? I’d appreciate some help. I keep breaking my brain over it :X

  13. thanks for the lesson. i tried to install a custom rom on my samsung galaxy exhilarate i577 not knowing anything about unlocking bootloader. now the phone is kinda dead, i mean it cannot boot up. so pls tell/help me on how to undo what i did inorder to make my phone work again pls help please i beg of you… thanks. you can also reach me on my e-mail with the solution(s) at nwokorochukwudibenedict@gmail.com thanks once more. happy val.

  14. Question, do you need to unlock the boot loader before you root. Pls, reply because I am only a newbie in android…

  15. Hello there, I want you to ask one thing, do you need to root first before you unlock the boot loader? Pls. Reply…

  16. Would have been nice to know this before I tried to install a custom ROM and bricked my phone…… Ahahahaha. I’m so stupid.

  17. In samsung devices that come with Touchwiz, is the bootloader already unlocked?
    Also, is there a way to check if the bootloader is locked or unlocked?

    • Considering that you typed the command to unlock it, I’m pretty sure it’s unlocked.

  18. My Sony Xperia have a locked bootloader and I was able to root with eboot. But I have to flash to an older version in recovery mode.

  19. you said that it wipes all internal memory apps, what does it mean? every app will be deleted? like messaging, browser…

  20. this guide is ONLY for nexus devices. i want to unlock bootloader of galaxy Music Duos GT-S6012. ANy help ?

  21. My friend, this is anything but complete guide ..
    Your article is rushed, scarce and it gives me an overall lack of confidence in your instructions …

    Next time:
    1. pick a target (acquire root or install custom rom)
    2. explain main steps from stock unrooted state to achieving target
    3. explain every step in detail

    Or, if you only want to emphasize on the bootloader explain the instructions and explain how to revert (if possible) and tell your readers what they can do after they unlocked the booloader (in order to achieve root or install a custom rom)

    And please, for the love of GOD, do emphasize the importance, the necessity of backups, failsafes and “in case of” scenarios ..

  22. by accident got to the bootloader screen and DO NOT want to unlock – what do I do there is no option for Yes or No. Only USB Control Init and USB Control Init end BUT can not do anything

  23. If I simply want to remove the Verizon bloatware to increase battery life, is unlocking bootloader the thing for me on my Rezound? I’m not interested in hacking or developing anything–just trying to get rid of useless apps and widgets. Or do I run the risk of running down a rabbit hole of endless fixes and add-ons by unrooting?

  24. After Unlocking Bootloader We Can Install CWM?
    Or When You Want To Install Custom ROM With CWM?

    Hey Please Answer

  25. So now I have unlocked the bootloader. Now what am I to do? I tried different softwares for s-off and root but it does not work at all. Plus, can I install a pre-rooted custom Rom without actually rooting my stock Rom in the first place. Plus, when I go to the HBoot screen, and click on recovery, it starts something and shows up a red time-out sign. Please someone help me out!

    Using Sensation Xe on 2.3.4. I seriously want ICS and sense 3.5 and fast. Also my email address: pethesahil@gmail.com

  26. If this happens to you, take out the battery and wait 5 minutes, to reset, it seems to happen when the battery is low charge. Thank You, to all.

  27. One can even unroot their phones…as I did and got it serviced from a service center free of charge as it was under warranty. Yes all phones don’t have the unroot option so please make a deep search in the internet whether your phone can be unrooted or not.

  28. One can even unroot their phones…as I did and got it serviced from a service center free of charge as it was under warranty. Yes all phones don’t have the unroot option so please make a deep search in the internet whether your phone can be unrooted or not.

  29. Anybody know how to check bootloader status for samsung galaxy tab 7″ p1000 android tablet?

    And the guide on how to root this tablet with the latest firmware (custom rom)?

  30. So will these instructions for unlocking the boot loader work for the original moto droid since it also has stock android?

    • No, it cannot you will need to ask your carrier to unlock your phone or try websites online that may be scams.

  31. Nice tuto, however i’m still confused at the core part where you have to download Fastboot.zip ! I can’t find it on the ModaCo’s website xD

    • you can place it anywhere…just unzip it,go to the folder and hold left shift+right click the mouse and select open command window here on windows….you should see the device when running the following code to continue…. fastboot devices

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