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Fastboot is a command line tool used to directly flash the filesystem in Android devices from a host via USB. It allows flashing of unsigned partition images. It is disabled in production devices since USB support has been disabled in the bootloader. You must have an Engineering SPL, or an SPL that is S-OFF.

After installing the Android SDK or ADB Standalone you can use 'fastboot' in addition to the more common ADB.


Verify SPL S-OFF

With the exception of the Google Nexus One (which has an OEM unlock), when you boot the device into the bootloader, you should see S-OFF (security off) on the top line. If you see S-ON, or you see a four-color rainbow background, the SPL does not support fastboot. You will need to install a fastboot compatable SPL, such as HardSPL or any of the Engineering SPLs for various devices. See the device specific page for further instructions.

Access bootloader

  1. Make sure you have ADB or the SDK installed.
  2. Download fastboot for the appropriate operating system for your computer.
  3. Place the executable in the proper place, usually:
    • Linux: ~/android_sdk/tools/ or ~/bin/
    • OS X: ~/android-sdk-macosx/platform-tools/
    • Windows: C:\android-sdk-windows\tools
  4. Turn off the device.
  5. Boot device into bootloader
  6. Make sure the device is in FASTBOOT and not HBOOT
  7. Connect the device to the computer via USB.
  8. On your computer, open terminal and run (you may need elevated privileges for this):
    fastboot devices
You should see something similar to:
List of devices attached 

fastboot --help

usage: fastboot [ <option> ] <command>

  update <filename>                        reflash device from
  flashall                                 flash boot + recovery + system
  flash <partition> [ <filename> ]         write a file to a flash partition
  erase <partition>                        erase a flash partition
  getvar <variable>                        display a bootloader variable
  boot <kernel> [ <ramdisk> ]              download and boot kernel
  flash:raw boot <kernel> [ <ramdisk> ]    create bootimage and flash it
  devices                                  list all connected devices
  reboot                                   reboot device normally
  reboot-bootloader                        reboot device into bootloader
  setserial <serial>                       set the device serial number
  setrev <rev>                             set the device hardware revision

  -w                                       erase userdata and cache
  -s <serial number>                       specify device serial number
  -p <product>                             specify product name
  -c <cmdline>                             override kernel commandline
  -i <vendor id>                           specify a custom USB vendor id
  -b <base_addr>                           specify a custom kernel base address
  -n <page size>                           specify the nand page size. default: 2048

Typical Partition Layout

For Reference when flashing partitions

Name Nandroid .img Information Contained Mount Point Notes
splash1 N/A Boot image ("T-mobile G1" image) mtdblock0? size: 320x480x2. Different from
recovery N/A A 'backup' kernel, initrd, and OS
for system recovery / maintenance
mtdblock1 Can flash custom recovery.img (Amon_Ra, ClockworkMod, etc).
Accessed by holding [home] while booting.
boot boot.img The main kernel and initrd mtdblock2 Can flash custom boot.img
system system.img The main OS mtdblock3 This is the /system partition
cache cache.img Temp storage mtdblock4 Unused. Can be re-partitioned.
userdata data.img User data and settings mtdblock5 This is the /data partition


Manual Nandroid restore

Make a Nandroid backup, and copy the folder off your SD card to your desktop.

cd ~/Desktop/path/to/backup/
fastboot flash userdata data.img
fastboot flash system system.img
fastboot flash boot boot.img
fastboot reboot

Flash Custom Recovery.img

fastboot flash recovery /path/to/<recovery>.img
fastboot reboot

Flash Custom boot.img

You should make a Nandroid backup first, in case you need to recover your boot.img

fastboot flash boot /path/to/<boot>.img
fastboot reboot


If you are developing a kernel, you may find it helpful to delete your boot.img and recovery.img to force booting into fastboot:

fastboot erase boot
fastboot erase recovery

You can then manually boot from your custom kernel and a ramdisk:

fastboot boot <kernel> <ramdisk>

Once you have a working kernel and ramdisk, you can automagically combine them within fastboot:

fastboot flash:raw boot <kernel> <ramdisk>
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