SkiffOS: Minimal Cross-compiled Linux for Embedded Containers

This mainline release corresponds to Buildroot 2021.11.2.

SkiffOS 2021.02.9 is the current LTS release.

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Changes since SkiffOS 2021.11.3:

 - Update docker, runc, etc.
 - Update linux to 5.16.11
 - Update rpi to 5.10.95
 - Update core/gentoo, core/alpine, skiff-core-ubuntu
 - Update nvidia-drivers to 470.103.01
 - Other minor fixes & tweaks

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SkiffOS is a lightweight operating system for any Linux-compatible computer, ranging from RPi, Odroid, NVIDIA Jetson, to Desktop PCs, Laptops (i.e. Apple MacBook), Phones, Cloud VMs, and more. It is:

• Familiar: uses simple Makefile and KConfig language for configuration.
• Flexible: supports any OS distribution inside containers w/ ssh drop-in.
• Portable: replicate the exact same system across any hardware or arch.
• Reliable: read-only minimal in-RAM host system boots reliably every time.
• Reproducible: offline and deterministic builds for reproducible behavior.

SkiffOS adds a configuration layering system to the Buildroot cross-compiler, which makes it easy to re-target applications to new hardware. Layers are merged together as specified in the SKIFF_CONFIG comma-separated environment variable. As a basic example: SKIFF_CONFIG=pi/4,core/gentoo starts Gentoo on a Raspberry Pi 4 in a Docker container.

The default configuration produces a minimal (~100Mb) in-RAM host OS with SSH and network connectivity, and includes a comprehensive set of debug tools. The host OS can be easily remotely updated with the push_image script, using rsync.

The "skiff/core" layer enables Docker ("apps/docker") and a default environment based on Ubuntu with a full graphical desktop environment. Others including "core/gentoo" and "core/dietpi" are available.

Most Linux devices have a unique set of requirements for kernel, firmware, and hardware support packages. The SkiffOS host OS separates hardware-specific support from the containerized user environments, simplifying management of updates across multiple hardware combinations.