Fastboot is a diagnostic protocol used primarily to modify the flash filesystem in Android smartphones from another computer over a USB connection. It is part of the Android Device Bridge library.

Use

Utilizing the Fastboot protocol requires that the device be started in a boot loader or Second Program 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. Some of most commonly used fastboot commands include:

• flash - Overwrites a partition in flash with a binary image stored on the host computer.
• erase - Erases a partition in flash.
• reboot - Reboots the device into the either the main operating system or the system recovery partition.
• devices - Displays a list of all devices (with Serial #) connected to the host computer.

Manufacturer support

Most retail Android devices have the fastboot protocol disabled at the factory in an attempt to prevent unauthorized tampering with the factory installed version of the Android software. While the T-Mobile G1 shipped without fastboot support, an engineering version of the bootloader with the protocol enabled was quickly leaked giving homebrew users full access to the device.

Other devices such as the Nexus S

Nexus S

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 and the Motorola Xoom

Motorola Xoom

The Motorola Xoom is an Android-based tablet computer by Motorola, introduced at CES 2011 on January 5, 2011. It was the first tablet to be sold with Android 3.0 Honeycomb. The Verizon branded Xoom was the first tablet to run Android 3.1 Honeycomb, however the 3.1 update has not yet been provided...

ship with fastboot disabled by default but can be enabled by running the "oem unlock" command. This will display a warning on the screen of the device informing the user that enabling the protocol will void their manufacturer warranty. Once the user accepts the terms the protocol is enabled and a security flag showing that the device has been unlocked is permanently set.