Skydock is a tool to customise Raspberry Pi OS images using Docker.

It's designed to enable automated creation of customised Raspberry Pi OS images for easy packaging and deployment of software.

• Run custom scripts inside the Raspberry Pi OS for configuration, software installation, and adding files.
• Expand the root file system for additional capacity.
• Add a FAT32 format data partition to the end of the image.

This tool should work with any Raspbian or RasPi OS image, it is currently tested with Raspbian Stretch Lite and RasPiOS Buster arm64. In general it should work with any Debian based OS targeting arm or arm64 architecture. However there are known networking issues with Ubuntu 20.04, and no other OSes have been tested.

More OSes for a wider range of devices may be added in future.

Pull the latest Skydock Docker image from the Quay.io repository with:

$ docker pull quay.io/wwwil/skydock:v0.3.0

A version tag should be given explicitly. Notes for each release can be found on the GitHub releases page.

Run Skydock like so:

$ docker run --privileged \
    -e SOURCE_IMAGE=/resources/raspbian-lite.img \
    -e MOUNT=/resources/customisations \
    -e SCRIPT=/customisations/customise.sh \
    --mount type=bind,source=$(pwd)/resources,destination=/resources \
    wwwil/skydock:v0.3.0

• SOURCE_IMAGE is the Raspberry Pi OS image to customise.
• MOUNT is a directory to mount inside the image for scripts and other files.
• SCRIPT is the script to run inside the image. This must be inside the MOUNT directory.

These resources must also be mounted into the Skydock Docker container. The --privileged option is required to allow Skydock to create loop devices.

A FAT32 format data partition can be added to the end of the .img if ADD_DATA_PART is set to true. The partition will be 64Mib in size, labelled DATA, and mounted at /data. The /etc/fstab and /boot/config.txt files will be updated with correct PARTUUIDs.

$ docker run --privileged \
    ...
    -e ADD_DATA_PART=true \
    ...
    wwwil/skydock:v0.3.0

This partition can be helpful when writing the .img to an SD card in macOS and Windows as data files can be placed there.

The main Raspbian partition can be expanded using the EXPAND environment variable. This will add the specified number of Mib to the end of the second partition before the data partition is added. For example, the main partition can be expanded by 200Mib like so:

$ docker run --privileged \
    ...
    -e EXPAND=200 \
    ...
    wwwil/skydock:v0.3.0

This can be helpful to add more space when installing large applications.

Travis is used to automatically build the Docker image and run tests. For tagged builds it also pushes the image to the registry on Quay.io.

GitLab CI is also used to build and test the image. This is because the two CI/CD systems seemed to handle loop devices differently. As Skydock is used by projects in both environments it is important that both are functional.