17twenty

So the Beaglebone uses the file uEnv.txt to store settings as it doesn't have any NAND allocated to do it with, by 
default the file is pretty empty save from the line:

optargs=run_hardware_tests quiet

You may have read a number of things about boot.scr etc  - ignore it, it's not correct.
The bootcmd is hardwired in uboot to do the following (i've seperated it all out to make things clearer) - you can see it by 
interrupting the bootsequence and performing a 'printenv'.

bootcmd=

iandanforth

#! /usr/bin/python

import optparse

def main(options):
    '''
    Performs the amazingly useful tasks for this command line tool
    '''
    pass