Fastboot is a protocol used by Android to diagnose and flash new firmware images on Android devices via USB. It is part of the Android Debug Bridge (ADB). For Samsung devices, use [download-mode] instead.
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)