[1vuio0pswjnm7]

I was making these all the time on NetBSD for dd'ing to USB sticks long before "Docker". FFS images containing only a bootloader and alternate kernels with embedded userlands. One was the "update" kernel and the other was the running kernel. I could pull out the stick after booting; I could also mount the stick and edit the update kernel. The userland was generally a single statically compiled binary, like busybox, but better. I thought about the possibilities of distributing software by bootable USB stick but not the possibilty that people might run the images in VM's.