boot2docker is a lightweight Linux distribution based on Tiny Core Linux made specifically to run Docker containers. It runs completely from RAM, weighs ~23MB and boots in ~5-6s (YMMV).

Head over to the Releases Page to grab the ISO.

Simply boot from the ISO, and you're done. It runs on VMs and bare-metal machines.

If you want your containers to persist accross reboots, just attach an ext4 formatted disk to your VM, and boot2docker will automount it on /var/lib/docker. It will also persist the SSH keys of the machine.

boot2docker auto logs in, but if you want to SSH into the machine, the credentials are:

login: docker
pass: tcuser

http://www.youtube.com/watch?v=QzfddDvNVv0

• Kernel 3.12.1 with AUFS
• Docker 0.7
• LXC 1.0-alpha2
• Container persistance via disk automount on /var/lib/docker
• SSH keys persistance via disk automount

boot2docker is built with Docker, via Dockerfiles.

It is composed in three disctinct steps:

• base: fetches, patches with AUFS support and builds the 3.12.1 Linux Kernel with Tiny Core base configuration
• rootfs: builds the base rootfs for boot2docker (not complete)
• running rootfs: when you run this image, it will build the rootfs, download the latest Docker release and create the .iso file on / of the container. This way you can update Docker without having to completely rebuild everything.

So the build process goes like this:

$ sudo docker build -t boot2docker-base base/
$ sudo docker build -t boot2docker rootfs/

Once that's done, to build a custom boot2docker.iso, just run the built rootfs image:

$ sudo docker run --privileged boot2docker
<CONTAINER_ID>
$ sudo docker cp <CONTAINER_ID>:/boot2docker.iso .

Why not CoreOS?

I got asked that question a lot, so I thought I should put it here once and for all. I liked the original idea of CoreOS: the smallest possible way to boot to docker. Unfortunately CoreOS has been growing larger and just did too many things for me. I just wanted the fastest way to boot to Docker.