sdm compatibility between RasPiOS versions

[gitbls]

sdm uses systemd-nspawn during customization. systemd-nspawn has compatibility issues when operating across RasPiOS versions.

Here's the general summary:

• Running on 32-bit RasPiOS: Can customize current release and prior release images. Does not work with any 64-bit images.
• Running on 64-bit RasPiOS: Can customize current release and prior release images, both 32-bit and 64-bit

The "doesn't work" scenario will either be a systemd-nspawn error (running on 32-bit and trying to systemd-nspawn into a 64-bit image), or a read-only file system once the nspawn has started.

Curiously, 64-bit Buster can systemd-nspawn into a 64-bit Bullseye image. We won't know definitively until the next Debian release after Bullseye if this is an anomaly due to how the 64-bit Buster beta was built or is standard behavior.

Your best bet is to use a current 64-bit release for the highest levels of compatibility for systemd-nspawn. For instance, sdm running on 64-bit Bullseye can customize 32-bit or 64-bit Buster, as well as 32-bit Bullseye.

How to build a customized 64-bit Bullseye image if all you have today is Buster?

• Blast 64-bit Bullseye onto an SSD/SD Card (without using sdm) and boot it
• Install sdm onto this 64-bit Bullseye
• Use sdm on 64-bit Bullseye to build your customized 64-bit Bullseye image, blast to SSD/SD Card, and boot
• That's it! You're now ready to customize Bullseye AND Buster images