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

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  • Aftab

    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

  • sam

    can Unlocking the Bootloader affects carrier network to be unlocked.

    • Aaron

      No but you can turn some 3G phones into a 4G phone with the rooting process.

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  • ajay

    if i again want to lock the boot loader…after unlocking it can i do it again??

  • yes you can

    fastboot oem lock

    works for locking :)

  • Chris

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

  • HolyShiits

    so that means, if i have flashed new rom into my phone, i have unlocked the bootloader?

  • ferraritm

    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)?

  • Aszca

    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.

  • Aszca

    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.

  • Mike Martinez

    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.

  • Pethesahil

    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

  • KIsHan

    Choduo chodta rego

  • Andres012279

    does this work for Droid X

  • AmirHashemieh

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

    Hey Please Answer

    • kachan64

      My phone allowing me to install by flashing to an older version.

  • Dude91

    can this work on samsung captivate?

  • dbase dekpor

    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?

  • marry

    hey if i agian wanna lock the bootldr menz after unlocking it can i do?????

  • Jane HP

    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

  • Arc S

    So thisWill work on my arc s as Long as i have stock?

  • GEORGE

    does it will beick my xperia x8 or not

  • GEORGE

    sorry i mean does it will brick my xperia x8 or not

  • http://twitter.com/edyshor = edyshor =

    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 ..

  • http://twitter.com/Bais01 Hafeez shaikh

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

  • Gio

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

  • kachan64

    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.

  • Dhananjay

    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?

  • Retard That Bricked His Phone

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

  • Anon

    Topic title is misleading. Should be how to unlock bootloader on Nexus devices

  • jo

    what do i do if the drivers dont install automatically?

  • Nuke-Cannon

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

  • Nuke-Cannon

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

  • chuks

    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.

  • Jonathan Tenebro

    pls help me to unlockbootloader on my T-Mobile HTC G2 phone help me

  • Papa Ozi

    How to unlock bootloader Hisense E860?

  • William Schuuring

    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

  • ابوملاك الحارثي
  • M Irfan Butt

    hi,
    please give me the link for unblocking the boot-loader for sky vega IM-A770K

  • FoolOfATook

    “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.

  • http://forum.xda-developers.com/member.php?u=5981373 thenookieforlife3

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

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