Sync SD card and offline copy

Put the SD card in a card reader on your PC/laptop.

Grow the second partition on the SD card to fill the card, or at least 3GB. I used https://wiki.gnome.org/Apps/Disks

Remove the existing files on both SD partitions. Assuming the SD card is mounted under /media/user: rm -rf /media/user/rootfs/* /media/user/boot/*

Extract buster_arietta_file_system onto the two partitions to your computer.

Then sync from the two directores to the SD card:

sudo /usr/bin/rsync -avH rootfs/ /media/user/rootfs && sync

sudo /usr/bin/rsync -avH boot/ /media/user/boot && sync

Be sure to "sudo" so that the file ownership for system files is correct.

Unmount the two SD card partitions

umount /dev/sdd1 umount /dev/sdd2

And check the partitions.

fsck -y /dev/sdd1 fsck -y /dev/sdd2

Insert the SD card into the Arietta and power up.