I need a unique, invariant number for use in software running on a Gumstix Overo WaterSTORM.

There is an article in the Wiki here that says the Gumstix has a unique, software-readable serial number:

http://docwiki.gumstix.com/index.php?title=Template:FAQ/Questions/a_software_accessible_unique

But, my /proc/cpuinfo (I am using Linaro on an SD) gives 0000000000000000 for the serial number.

There is no u-boot environment variable named "serial" either.

There is a u-boot environment variable named "dieid#", but I can change it, and we have one system that writes the entire u-boot environment block on setup, and in any case it can't be trusted.

So the question remains, is there some kind of software-readable, unique, invariant serial number that can be read from these boards? The wiki seems to be entirely off.

Thanks!
Jason