Fastboot is a protocol used by Android to diagnose and flash new firmware images on an Android devices via USB. It is part of the Android Debug Bridge (ADB).
What is fastboot intended for?
Fastboot supports a rather limited set of actions. Its primary uses include:
- flashing images (complete device-firmware or separate partition images, but also radio-firmware)
- erase/wipe partitions
- boot a specific kernel
- lock/unlock the bootloader
What fastboot does not do
Don't mis-interpret its name to be a "fast alternative to boot your device" (unfortunately, some manufacturers like HTC and Sony have a similarly named "Fast Boot" option). Admitted, a start into fastboot mode is faster -- but that's due to the fact it only needs a limited set of libraries etc. It does e.g. not start Zygote or the System Server (see: Can somebody explain the boot process of an Android device? -- that's what above mentioned "Fast Boot" option on some devices does for a "fast boot": killing the System Server; Unix-Users might compare that to killing the X-Server), so no GUI and no apps here. Neither does it offer a full set of commands (shell access) or the like. As described, it's just a very minimal system for a very specific purpose.
How do I get my device into fastboot mode?
Multiple ways for that:
- when already connected to your computer via adb:
adb reboot bootloader
- with the device being switched-off: Press and hold volume up and power keys, release when boot completed (if that doesn't work, add the volume down button to the key combo, making it 3 buttons to simultaneously press-and-hold)
- with the device being powered up in "normal mode" and the screen being switched on: long press the power button to bring up the power menu. Some ROMs have a shortcut here. On some, long-pressing the "reboot" option here brings it up.
Some good questions and answers tagged fastboot
- What does “fastboot oem lock” do?
- I can FastBoot my device. How can I reinstall an Android image to it?
- Unlock bootloader using fastboot using Ubuntu/Linux
- can fastboot be used to backup device? (short summary of what fastboot can do and what not)
Ever-returning Troubleshooting questions
- fastboot doesn't see device (Windows)
- ADB can discover devices but not fastboot (Linux)
- adb can find device but fastboot cannot (Linux)