Rooting a mobile device can be a fairly simple task depending on its manufacturer. Some brands, such as Motorola, offer every facility to unlock their devices by publishing on its website the instructions and files needed to do so.

However, other companies adopt a completely opposite policy, and try as hard as possible to avoid this possibility. We will not enter here into the reasons for adopting one or another attitude and instead, we are going to focus on how to unlock the G3, despite all the attempts by the South-Korean company to avoid it.

If you have ever rooted an Android device, you already know the steps. If this is your first time, here you will find the instructions to do it properly. Basically, you must follow 3 steps: Enable USB debugging mode, download, run and install Purple Drake and SuperSU from Play Store, and unblock the bootloader. Let’s see it by parts:

How to Enable USB debugging mode

USB debugging is used to install apk files on our mobile device when we have it connected to the PC via a USB cable. To activate this mode, we must access to the information menu and press 10 times on the “build number”.

Then, we will see a new option on the Settings menu called “development menu”, and inside, we can find the option to enable USB debugging.

How to download and execute Purple Drake and SuperSU

Purple Drake is an application very useful throughout the process of rooting and unlocking the bootloader on our terminal. We can download it here and once installed, we can go to the Play Store and also install the SuperSU.

One thing we should keep in mind before we start the process is that it does not work for all G3 models. If we have a Verizon or Sprint device, these steps are not going to work. For all other cases, we need to know the exact model of our G3. We can do it by going to the General option of the Settings menu. Once there, we must go to “Hardware Information” and find the exact model of our device.

Remember that once we have the phone rooted, we should not install OTA updates. If we do, we will lose root permission.

Unlocking the bootloader

Now we just need to unlock the bootloader. To do this, the easiest way is to install the bumped TWRP recovery.

We have to save it in the root of the phone and type the following commands from the PC terminal:

• adb shell
• su
• dd if=/dev/zero of=/dev/block/platform/msm_sdcc.1/by-name/recovery
• dd if=/sdcard/twrp-2.8.0.0_MODEL-signed.img of=/dev/block/platform/msm_sdcc.1/by-name/recovery
• ##In MODEL we should type our LG model to match the downloaded file

At this point, we just need to do a wipe factory reset to the device. Remember that this process completely erases all the data stored, so we must be sure to have a backup.

Now we can proceed to boot the phone with the custom of TWRP recovery and enjoy our new phone fully unlocked!

Source: Unfortunately, the source was lost somewere in internet.
Here is where we saw it for the last time http://www.elandroidelibre.com/2014/10/como-rooting-and-unlock-the-bootloader-the-lg-g3.html.