mjhjmtu

I'm currently looking at how Docker works. As far as I did know Docker does not boot, it just starts a process in a very chrooted environment. But when I look in some documentation some mention that Docker has a bootfs. It's a filesystem that only mounts at boot and unmounts just after rootfs is mounted (I guess). But you can't see or touch it. I even can't find it.

Is it still true that Docker uses some kind of bootfs? For example, these articles confuse me: http://collabnix.com/understanding-docker-container-image/. It has bootfs with kernel and cgroup in it. But as far as I know, the kernel is outside of Docker, that is part of the host system.

My main question is, is it still true that Docker uses bootfs to 'start' a container? And, where can I see that filesystem?

I think you may have discovered a bit of misleading folklore. I did a Google site-search for "bootfs" (i.e. site:docker.com bootfs) and found almost nothing - literally four results. I searched through each of these four results and I will describe what I found.

• Docker v1.9 Documentation: Images and Containers

This describes the structure of images and containers and their relation to storage drivers. The string "bootfs" does not appear on this page. Neither does the string "boot" for that matter.

• Docker White Paper: Introduction to Container Security

This document describes the Docker container implementation from a security perspective. The string "bootfs" appears only once - in a diagram in which it appears to refer to the boot file-system of the host machine.

• Docker Forums: Linux distro compatibility between host and container

In this forum discussion the string "bootfs" appears exactly once - again in reference to the host machine, not to a container.

• Docker Qemu builds

Here the string appears as a substring in various package names. There's no indication that it relates to starting a Docker container.

I also searched the Docker CE GitHub but didn't find any instance of the string "bootfs".

After many Google searches of the form "docker bootfs location" and "where is docker bootfs" I found several results which seemed to indicate that the idea of a Docker bootfs existing at the container level is a misnomer. Here are a couple such results:

• Padge Blog: Containers Don't Really Boot

This blog post describes the Docker start-up process in some detail and distinguishes it from a typical boot process.

• Moby Github Issue: how i upgrade bootfs

In this issue discussion a contributor refers to bootfs as a "concept" that "you can't touch".

That article confuses you because it is non-canonical and nonsense. It is not true that Docker uses anything called a bootfs, and Docker does not require /boot. Docker containers do not use an initramfs and kernel of their own. It's quite possible several "articles" have copied the same garbled source without attribution. You should ignore all of them.