Build a custom ev3dev install image with Mono

As far as I've tested, Mono 5.* (or higher) is impossible to install on ev3dev on device because of the mono-roslyn package, which requires too many RAM, goes to the swap and thus is impossible to be installed on battery power. Actually, I didn't manage to await the installation finish even on AC power. But you can avoid this issue with flashing your device with your own installation image of ev3dev with mono preinstalled.

To create it, you will need system with:

• git installed
• ability to run Docker engine
• ability to execute brickstrap script from the ev3dev project

I've personally used Ubuntu 22.04 but I reckon any other system with bash should do =) I will also use Visual Studio Code as text editor, but if you prefer another one, you can freely change code in script samples with vim, nano or any other of your choice.

1. Install the Docker engine

Official documentation should work just fine.

2. Check out ev3dev/docker-library

You can find the project's home here https://github.com/ev3dev/docker-library. Clone it to a directory of your choice, we will work right inside it later:

git clone https://github.com/ev3dev/docker-library.git

Let's say that your checkout directory is docker-library.

3. Prepare base docker images

Probably this is not the most efficient way to handle docker images, but it will do for us. We need to create two base images of ev3dev and then create our own on top of them. I'll suppose that you will use stretch as distro core and LEGO EV3 as the device, you can find the necessary directories and files just next to the files I'm going to use now. Lets start with the base images:

cd docker-library/ev3dev-stretch
sudo docker build -t ev3dev/ev3dev-stretch-ev3-base -f ev3-base.dockerfile .
sudo docker build -t ev3dev/ev3dev-stretch-ev3-generic -f ev3-generic.dockerfile .

4. Prepare our own Docker image

Next, let's create our own Docker image. First, we need to add a new layer with our scripts that will install mono on our image. Assuming we're still inside docker-library/ev3dev-stretch directory, create a layer directory and an installation script file:

mkdir -p layers/mono/brickstrap/mono
code layers/mono/brickstrap/mono/run

And insert following content to it:

#!/bin/bash

apt-get install --yes dirmngr ca-certificates gnupg apt-transport-https
gpg --homedir /tmp --no-default-keyring --keyring /usr/share/keyrings/mono-official-archive-keyring.gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb [signed-by=/usr/share/keyrings/mono-official-archive-keyring.gpg] https://download.mono-project.com/repo/debian stretch/snapshots/5.10.1.47 main" | sudo tee /etc/apt/sources.list.d/mono-official-stable.list
apt-get update

apt-get install --yes gcc gdb mono-complete

You can see that I've used version 5.10.1.47. That is the version I've tested but you can try others if you need to.

Next, create a file docker-library/ev3dev-stretch/ev3-mono.dockerfile:

code ev3-mono.dockerfile

Add the following content to it:

FROM ev3dev/ev3dev-stretch-ev3-generic
COPY layers/mono/ /
RUN /brickstrap/mono/run
ARG BRICKSTRAP_IMAGE_NAME=custom-ev3dev-stretch-ev3-mono
ENV BRICKSTRAP_IMAGE_NAME ${BRICKSTRAP_IMAGE_NAME}
RUN echo "$BRICKSTRAP_IMAGE_NAME" > /etc/ev3dev-release

And build the image with command:

sudo docker build -t custom-ev3dev-stretch-ev3-mono -f ev3-mono.dockerfile .

5. Install brickstrap

The easiest way to do it is by using apt:

sudo add-apt-repository ppa:ev3dev/tools
sudo apt update
sudo apt install brickstrap

If it's not suitable for you, see the tool's main page.

6. Create system image

This is a two-step process. First, you need to create .tar archive with the image content with brickstrap. Next, you'll use brickstrap to convert the archive to an .img file. You can perform the following commands in any directory that you don't mind to put files into:

sudo brickstrap create-tar custom-ev3dev-stretch-ev3-mono ./custom-ev3dev-stretch-ev3-mono.tar
sudo brickstrap create-image ./custom-ev3dev-stretch-ev3-mono.tar ./custom-ev3dev-stretch-ev3-mono.img

These commands may take a while. If you want to know more about these commands, you can check the brickstrap manual page.

The resulting custom-ev3dev-stretch-ev3-mono.img file is the one you need to flash on your EV3 device. It should be almost identical to the image you can download from the ev3dev site except the mono installed.