Awesome

pimod

Reconfigure Raspberry Pi images with an easy, Docker-like configuration file.

About

pimod overtakes a given Raspberry Pi image file by mounting a copy and modifying it within a QEMU chroot. This allows the execution of a Pi's ARM code on whatever target, e.g., a x86_64 host.

To ease the usability, a Docker-inspired recipe, called the Pifile, is used to instrument pimod.

# Example Pifile to create a customized version of the Raspberry Pi OS Lite

# Based on a remote image, which will be cached locally, create the altered raspi_example.img file
FROM https://downloads.raspberrypi.org/raspios_lite_arm64/images/raspios_lite_arm64-2023-02-22/2023-02-21-raspios-bullseye-arm64-lite.img.xz
TO rapsi_example.img

# Increase the image by 100 MB
PUMP 100M

# Install an ssh key from local sources
RUN mkdir -p /home/pi/.ssh
INSTALL id_rsa.pub /home/pi/.ssh/authorized_keys

# Enable the serial console and SSH
RUN raspi-config nonint do_serial 0
RUN raspi-config nonint do_ssh 0

# Install the important cowsay util
RUN apt-get update
RUN apt-get install -y cowsay

Installation, Usage

Usage: pimod.sh [Options] Pifile

Options:
  -c --cache DEST   Define cache location.
  -d --debug        Debug on failure; run an interactive shell before tear down.
  -h --help         Print this help message.
  -r --resolv TYPE  Specify which /etc/resolv.conf file to use for networking.
                    By default, TYPE "auto" is used, which prefers an already
                    existing resolv.conf, only to be replaced by the host's if
                    missing.
                    TYPE "guest" never mounts the host's file within the guest,
                    even when such a file is absent within the image.
                    TYPE "host" always uses the host's file within the guest.
                    Be aware that when run within Docker, the host's file might
                    be Docker's resolv.conf file.
  -t --trace        Trace each executed command for debugging.

Docker

Getting or Building the Docker Image

There are pre-built images available on Docker Hub:

docker pull nature40/pimod

Alternatively, you can simply build the image yourself locally. This is essential for development, among other things:

git clone https://github.com/Nature40/pimod.git
cd pimod
docker build -t nature40/pimod .

Using the Docker Image

Afterwards, the Docker image can either be used by docker or docker compose:

# Using Docker:
docker run --rm --privileged -v $PWD:/pimod nature40/pimod pimod.sh examples/RPi-OpenWRT.Pifile

# Using Docker Compose:
docker compose run nature40/pimod pimod.sh examples/RPi-OpenWRT.Pifile

Debian

Of course, Docker isn't really necessary and pimod can also be used on, e.g., a Debian directly:

sudo apt-get install \
  binfmt-support \
  fdisk \
  file \
  kpartx \
  lsof \
  p7zip-full \
  qemu \
  qemu-user-static \
  unzip \
  wget \
  xz-utils \
  units

sudo ./pimod.sh Pifile

GitHub Actions

Pimod can also be used as a GitHub Action and is available on the marketplace.

name: tests
on: push

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@v3
        with:
          submodules: recursive
      - name: Run pimod OpenWRT example
        uses: Natur40/pimod@master
        with:
          pifile: examples/RPi-OpenWRT.Pifile

Pifile

The Pifile contains commands to modify the image.

Those commands are grouped in stages which pimod executes in their corresponding order.

• First, all setup stage commands are being executed to download the base image and configure the output.
• The prepare stage follows which pre-flight commands, e.g., resizing the output image.
• The action happens in the chroot stage where the QEMU chroot is built, commands are executed within, files are copied and so on.
• Finally, the postprocess stage might clean up some things.

However, as the Pifile being just a Bash script by itself and the commands are functions, which are loaded in different stages, Bash scripting is possible within the Pifile to some extend.

More internals are documented in our our scientific paper. If you stumble upon details there that you think belong in this README, feel free to create an issue or pull request.

Example

$ cat Upgrade.Pifile
FROM 2018-11-13-raspbian-stretch-lite.img

PUMP 100M

RUN raspi-config nonint do_serial 0

RUN apt-get update
RUN bash -c 'DEBIAN_FRONTEND=noninteractive apt-get -y dist-upgrade'
RUN apt-get install -y sl

# The Upgrade.Pifile will create, called by the following command, a new
# Upgrade.img image based on the given Raspbian image. This image's size is
# increased about 100MB, has an enabled UART/serial output, the latest software
# and sl installed.
$ sudo ./pimod.sh Upgrade.Pifile

# Write the new image to a SD card present at /dev/sdc.
$ dd if=Upgrade.img of=/dev/sdc bs=4M status=progress

Further and more expressive examples are available in this repository's ./example directory. Please take a look and feel free to submit your own examples if they are covering a current blind spot.

Commands

Stage independent

INCLUDE PATH_TO_PIFILE

INCLUDE includes the provided Pifile in the current one for modularity and re-use. The included file has to have a .Pifile extension which need not be specified.

1. Setup Stage

FROM PATH_TO_IMAGE [PARTITION_NO], FROM URL [PARTITION_NO]

FROM sets the SOURCE_IMG variable to a target. This might be a local file or a remote URL, which will be downloaded. This file will become the base for the new image.

By default, the Raspberry Pi's default partition number 2 will be used, but can be altered for other targets.

TO PATH_TO_IMAGE

TO sets the DEST_IMG variable to the given file. This file will contain the new image. Existing files will be overridden.

Instead of calling TO, the Pifile's filename can also indicate the output file, if the Pifile ends with ".Pifile". The part before this suffix will be the new DEST_IMG.

If neither TO is called nor the Pifile indicates the output, DEST_IMG will default to rpi.img in the source file's directory.

INPLACE FROM_ARGS...

INPLACE does not create a copy of the image, but performs all further operations on the given image. This is an alternative to FROM and TO.

2. Prepare Stage

PUMP SIZE

PUMP increases the image's size about the given amount (suffixes K, M, G are allowed).

3. Chroot Stage

INSTALL <MODE> SOURCE DEST

INSTALL installs a given file or directory into the destination in the image. The optionally permission mode (chmod) can be set as the first parameter.

EXTRACT SOURCE DEST

EXTRACT copies a given file or directory from the image to the destination.

PATH /my/guest/path

PATH adds the given path to an overlaying PATH variable, used within the RUN command.

WORKDIR /my/guest/path

WORKDIR sets the working directory within the image.

ENV KEY [VALUE]

ENV either sets or unsets an environment variable to be used within the image. If two parameters are given, the first is the key and the second the value. If one parameter is given, the environment variable will be removed.

An environment variable can be either used via $VAR within another sub-shell (sh -c 'echo $VAR') or substituted beforehand via @@VAR@@.

ENV FOO BAR

RUN sh -c 'echo FOO = $FOO'   # FOO = BAR - substituted within a sh in the image
RUN echo FOO = @@FOO@@        # FOO = BAR - substituted beforehand via pimod

ENV FOO

RUN CMD [PARAMS...]

RUN executes a command in the chrooted image based on QEMU user emulation.

Caveat: because the Pifile is just a Bash script, pipes do not work as one might suspect. A possible workaround could be the usage of bash -c:

RUN bash -c 'hexdump /dev/urandom | head'

HOST CMD [PARAMS...]

HOST executed a command on the local host and can be used to prepare files, cross-compile software, etc.

Pifile Extensions

Because the Pifile is just a Bash script, some dirty brilliant hacks and extensions are possible.

Bulk execution

Sub shells can be used with the RUN command.

RUN sh -c '
apt-get update
DEBIAN_FRONTEND=noninteractive apt-get -y dist-upgrade
apt-get install -y sl
'

Inplace Files

Here documents can also be used to create files inside of the guest system, e.g., by using tee or dd.

RUN tee /bin/example.sh <<EOF
#!/bin/sh

echo "Example output."
EOF

Scientific Usage & Citation

If you happen to use pimod in a scientific project, we would very much appreciate if you cited our scientific paper:

@inproceedings{hoechst2020pimod,
  author = {{Höchst}, Jonas and Penning, Alvar and Lampe, Patrick and Freisleben, Bernd},
  title = {{PIMOD: A Tool for Configuring Single-Board Computer Operating System Images}},
  booktitle = {{2020 IEEE Global Humanitarian Technology Conference (GHTC 2020)}},
  address = {Seattle, USA},
  days = {29},
  month = oct,
  year = {2020},
  keywords = {Single-Board Computer; Operating System Image; System Provisioning},
}

Notable Mentions

• Debian Wiki, qemu-user-static
• raspberry-pi-chroot-armv7-qemu.md
• chroot-to-pi.sh
• PiShrink
• pi-bootstrap