Format Appliance OS Thing

A mistake cool thing.

This appliance OS has one goal in life: to put a new MBR disk label and format a FAT32 partition on the first partition of that new labeled disk, then sync the writes to disk and power off.

This is accomplished with a very minimal Linux kernel configuration and static builds of multiple open source software packages, along with a custom "init" written in C++ which does the magic.

This appliance is designed to be used with QEMU's "microvm" machine; a sample run script to test it is provided in ./run. It boots very quickly, and performs its work in under 3 seconds.

Why make this?

Two answers:

• While it is true that a "template image" set would be easier, this would quickly begin to fall apart if multiple filesystems are desired. A single appliance that can catch-all safely is a better approach.

• I wanted to learn about microvms and building special-cased appliance OSes, and do so hands-on with a task that I needed at the time. This is, honestly, 90% of why I did it, but hey; learning isn't a bad thing.

Building

• Download the x86_64 musl toolchain from musl-cross's Releases page. Extract it and rename the directory it output to /toolchain. This will be the toolchain used for the build.

• Copy sources/crossfile.sample.txt to sources/crossfile.txt, and alter the system root path to match where you placed this repository. (probably at some point this will be generated, but for now this step has to exist)

• Run ./get_packages.sh to get and extract all the external packages.

• Use ./build.sh to build everything.

• ...

• profit? (output/ will contain the bzImage and initramfs image).

Usage

./run provides a good starting point for using the appliance.

Quiet down the log level (the minimum required is probably console=ttyS0 reboot=t), and that should be enough to get going.