How can I get the fastboot command? I'm trying to root my KF 6.3 following this article. 
http://forum.xda-developers.com/showthread.php?t=1568340&amp;page=1

Now I'm in Kindle Fire screen (fastboot mode) but fastboot is missing.


hieund@hieund:~/Downloads/KF/RestoreRootFor6.3$ fastboot -i 0x1949 flash bootloader u-boot.bin
fastboot: command not found


I am on Ubuntu 12.04 and have adb installed.
Fastboot is a binary and protocol used to communicate with Android devices in the early boot stage. It allows to change of the boot target and therefore is often used to install custom boot-loader (TWRP, clockworkmod, etc.) and ROMs.

The binary often comes with the Android SDK, for example on my linux system it is installed at /opt/android-sdk-update-manager/platform-tools/fastboot. There are also build instructions for fastboot on the official android page.