Fastboot is a a special diagnostic and engineering protocol used to update the flash filesystem in Android devices from a host over USB. It allows flashing of unsigned partition images. The fastboot utiity is part of the Android SDK. It allows a developer to modify contents of the flash and to test out custom boot images devoped by 3rd parties. Its couterpart, adb, can be used to boot your device into fastboot mode with the command “adb reboot-bootloader“.
Please be aware that you can easily wipe out the bootloader on your device, so use this utility with caution.
Fastboot can run on Windows, Mac, and Linux operating systems. Utilizing the Fastboot protocol requires that the device to be started in a boot loader mode in which only the most basic hardware initialization is performed. After enabling the protocol on the device itself, it will accept any command sent to it over USB via a command line tool on your PC.
Fastboot can also boot the phone using a kernel image or root filesystem image which reside on the host machine rather than in the phone’s flash memory.
You can enter Fastboot mode via ADB command if the device is already connected to a host device through an ADB interface.
On a Dragon Board platform, you can also boot into Fastboot mode by holding the ’4′ button while booting up.
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