Thanks, that worked.
What I did:
- Create GPT partition table on USB device with only one ext4 partition with the label “APP” (the docs suggest so, but it’s probably not significant)
- Clone the mounted and running system to the USB device (method suggested by the Arch Wiki):
$ sudo e2image -ra -p /dev/mmcblk1 /dev/sda1 -f
- Edit
/boot/extlinux/extlinux.conf
on USB device to boot from/dev/sda1
instead of/dev/mmcblk1
.
(I tried with de UUID instead of/dev/sda
but it didn’t work, maybe I wrote it incorrectly).