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.


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 thedevice specific page for further instructions.Verify SPL S-OFF

Access bootloader

  1. Make sure you have ADB or the SDK installed.
  2. Linux & OS X only: 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:
    • Windows: C:\Android_SDK\Tools or C:\Program Files\adb
  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:
    fastboot devices
You should see something similar to:
List of devices attached
HTXXXXXXXXXX	device

fastboot –help

usage: fastboot [ <option> ] <command>

commands:
 update <filename>				reflash device from update.zip
 flashall					flash boot + recovery + system
 flash <partition> [ <filename> ]		write a file to a flash partion
 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
 continue					continue with autoboot
 reboot						reboot device normally
 reboot-bootloader				reboot device into bootloader

options:
 -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 bootanimation.zip.
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

Examples

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

Development

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>
Source : Cyanogenmod