I created a successfully bootable micro sd card using these instructions http://gumstix.org/create-a-bootable-microsd-card.html from a custom built image using yocto.

One thing which has perplexed me is that, when i boot the sd card and i write to the SD card from my ubuntu build box, i do not see that change reflected when i login via serial on the gumstix!!! If i create a file on the gumstix, and i plug that sd card into my ubuntu machine, i do not see the file..

I always thought a bootable micro sd card uses the second ext3 partition as the rootfs!! 

Can anyone explain what is going on?