The adafruit-pi-externalroot-helper script is mostly an implementation of the process outlined in paulv's HOWTO: Move the filesystem to a USB stick on the Raspberry Pi forums, with additional help from the following sources:

The Arch Linux wiki, GUID Partition Table for what a GPT is and some parted commands.
GUID Partition Table, Wikipedia.
Booting from an external USB drive, from the Raspberry Pi StackExchange.
Booting a Raspberry Pi reliably from USB in the presence of multiple USB drives, by Stefan Krastanov.
Speed up your Pi by booting to a USB flash drive, by Sam Hobbs.
This comment on root= in init/do_mounts.c in the Linux source tree.

While the steps here are fairly straightforward once you put them together, this can be a finicky process. If you run into any problems, please consider filing an issue on the GitHub project.

This guide was first published on Apr 13, 2015. It was last updated on Apr 13, 2015.

This page (Further Reading) was last updated on Apr 13, 2015.

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