Raspbian-based Docker Images

This repository contains my raspbian-based docker containers.

qemu-user-static is used to run binaries compiled for the Raspberry Pi. There is a significant performance impact compared to native application performance, but on modern x86 hardware the performance hit isn't totally crippling.

Setup On Arch Linux

You will need to install several packages from AUR. Personally, I prefer to use pacaur for accessing packages in AUR. Replace pacaur as necessary.

pacaur (build script uses pacaur)
qemu-user-static (needed for qemu-arm-static)
binfmt-support
binfmt-qemu-static
debootstrap
arm-linux-gnueabihf-gcc

qemu and binfmt are used to enable native execution of armhf from an x86 machine.
debootstrap is, of course, used to generate the rootfs

Get binfmt working:

Create/edit /etc/qemu-binfmt.conf:

EXTRA_OPTS="-L/usr/lib/gcc/arm-linux-gnueabihf"

To get binfmt working without rebooting:

sudo systemctl restart systemd-binfmt
sudo update-binfmts --enable

To verify binfmt is setup properly for arm:

[tbeck@hamburgler base]$ cat /proc/sys/fs/binfmt_misc/qemu-arm
enabled
interpreter /usr/bin/qemu-arm-static
flags: OC
offset 0
magic 7f454c4601010100000000000000000002002800
mask ffffffffffffff00fffffffffffffffffeffffff

Note that if binfmt is not configured properly, you will see errors such as:

[tbeck@hamburgler base]$ sudo chroot rootfs/ \
> /debootstrap/debootstrap --second-stage --verbose
chroot: failed to run command ‘/debootstrap/debootstrap’: Exec format error

Be sure to restart systemd-binfmt and update-binfmts.

[tbeck@hamburgler base]$ rootfs/bin/ls
/lib/ld-linux-armhf.so.3: No such file or directory

Be sure that the /etc/qemu-binfmt.conf file has EXTRA_OPTS set to the right path. On arch, this path is usually somewhere in /usr/lib/gcc/, e.g. /usr/lib/gcc/arm-linux-gnueabihf

You should now be ready to proceed.

Installing a local rootfs

We'll use fakeroot and debootstrap to build a raspbian-based rootfs.

# mkdir rootfs
# fakeroot debootstrap --foreign --no-check-gpg --include=ca-certificates --arch=armhf stable rootfs http://archive.raspbian.com/raspbian

This will setup the stable (currently jessie) raspbian into the directory rootfs. The command may take some time to complete.

Add qemu-arm-static temporarily to enable execution within the chroot environment:

# cp `which qemu-arm-static` rootfs/usr/bin/

Now fixup permissions and run the second-stage (configure) bootstrap:

# sudo chown -R root:root rootfs
# sudo chroot rootfs /debootstrap/debootstrap --second-stage --verbose

This will take some time to complete as well.

At this point, we have enough to get going for Docker - users wishing to build their own raspberry pi environment would continue to add the rpi firmware, kernel, and boot files. Since docker images require none of these, we'll skip them.

# sudo rm rootfs/usr/bin/qemu-arm-static

Before you tar the rootfs, consider tidying up a bit. If you're ready to proceed, you can build the rootfs.tar.gz file:

# sudo tar -czf rootfs.tar.gz -C rootfs .

Rootfs cleanup

TODO

Building the container

To build the container, copy of the rootfs.tar.gz file into the docker context (where the Dockerfile is) and in the same directory run

# docker build .

Don't forget to docker tag, docker push, and docker pull as needed!

Running the container

Run the container just like you would any other docker container:

# docker run -it <image> /bin/bash

Is sufficient to get you to a prompt.