First step to get anywhere is to get ROS2 and the camera working. Which ideally would have been a matter of some apt-gets. Except there were a few complications:

• ROS2 is native to Ubuntu LTS.
• Latest LTS is Ubuntu 22.04.
• Camera Module 3 is a new module from 2023 and requires the latest camera library and Kernel Drivers. Otherwise it ain't detected.
• Only the new Debian based Raspberry Pi OS and Ubuntu 23.10 have this.
• So no native binaries exist...

This means that i don't get a easy "apt install ros-iron" and call it a day. Either i need to get the driver working on the older distro, wait till may 2024 for a new LTS ubuntu + ROS2, or get ROS2 working on the newer via alternative means. Since the driver is meant for a significantly newer Linux Kernel and i know nothing about drivers, the former is pretty much off the table. I gotta find a different way to get ROS2.

There are two ways to do this.  Either i build it myself OR i use a Docker container.

I would prefer not to wrestle with docker just yet, even though it is the easiest way to get things running. If i can run something without any overhead i'd rather use that. so i figured building ROS2 would be worth a try. I can always try to migrate to a newer Distro with Docker later and see if it has any impact.

Let me pre-empt by saying I came to regret this decision and urge anyone to just use the 24.04 LTS+ROS2 Jazzy (if available by time of completion) or use Docker to run it on Raspberry Pi OS. The following is more for the curious/brave. Took weeks to get things compiled and working on a Zero2 (memory contraints). NO Guarantee the following even works!!!

How to BUILD ROS2 on RPi Ubuntu Server 23.10:

This is assuming a freshy flashed OS just booted into for the first time and is being accessed via SSH.

Step 1) Prep the Distro.

First things first. Ubuntu doesn't start with swap space, which isn't a good thing on a tiny pi like the zero2. Gotta get that fixed, preferably before the Kernel starts to throw a fit and the Pi freezes. First we allocate about 2Gb to a swapfile, Give it permissions and than make it a swap.

sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

 We now have a 2GB Swap file ready and active. To make it permanent, we open up the fstab file:

sudo nano /etc/fstab

And add as entry:

/swapfile swap swap defaults 0 0

 So that it will always be active whenever the Pi is started.

After that we go through the apt upgrade and apt update routine (you should know how it goes)

Step 2) Get the prerequisites

Time to get the first set of prerequisites needed. Run the following command:

sudo apt install -y git colcon python3-rosdep2 vcstool wget python3-flake8-docstrings python3-pip python3-pytest-cov python3-flake8-blind-except python3-flake8-builtins python3-flake8-class-newline python3-flake8-comprehensions python3-flake8-deprecated python3-flake8-import-order python3-flake8-quotes python3-pytest-repeat python3-pytest-rerunfailures python3-vcstools tmux

 This should hopefully get every that is needed. If some parts don't install, note them down for later checking. Some python parts may not want to install via the apt install approach. Often you can try to forcefully install them anyway via "-pip install (PACKAGE) –break-system-package". The break package flag tells it to ignore the system package manager and do it anyway.

Step 3) Prep the source and get the ROS dependancies

mkdir -p ~/ros2_iron/src
cd ~/ros2_iron
vcs import --input https://raw.githubusercontent.com/ros2/ros2/iron/ros2.repos src
sudo rm /etc/ros/rosdep/sources.list.d/20-default.list

sudo apt upgrade
sudo rosdep init
rosdep update

rosdep install --from-paths src --ignore-src -y --skip-keys "fastcdr rti-connext-ds-6.0.1 urdfdom_headers"

With this. Everything should be there to let one build. But don't do it yet!!

Step 4) Ignore unused parts

Now it is of vital importance to start disabling parts we ain't going to use. Especially if you are using a tiny pi like the Zero2. If you don't. It will try to build very large components we don't need like Navigation, desktop components and 3D Robotic visualization stuff that will overflow rapidly into SWAP and cause the building to take bloody MONTHS....

The trick to do so. Is to make liberal use of the "COLCON_IGNORE" flag file. This is a empty file that if found by colcon in a folder, causes it to ignore everything inside that folder. Carefully placing it here and there can help cut down the work by like 90% really. To make it convenient to spread it around. I used winSCP to get a explorer like window through which to easily copy-paste the flag file.

Here is a list where i dropped some Ignores:

• /ros2/rviz/
• /ros-perception
• /ros-planning
• /ros-tooling
• /ros-visualization

Step 5) Build & Pray!

Now to pull the trigger.

First things first: Be sure you are in a tmux session.
This process will take AGES and you'd rather not have it stop the moment you close the SSH session or connection drops. Once inside a tmux session: just enter ros2_iron folder (if not already there) and execute the command:

colcon build --symlink-install --executor sequential

 The PI will start working on compiling ROS2 for you.

Astute may notice the Executor flag. This forces the system to work on each package individually in sequence, rather than try to work on multiple in parallel. This is mainly for the sake of memory as running multiple compilations at the same time quickly fills it up and if that happens compilation will go at less than 10% speed. If your Pi is beefier you can swap it out with "--parallel-workers 2" to make it use two threads or just omit the flag all-together to go full-throttle. For such users this shouldn't take too long.

While its busy, Detach from the tmux session (CTRL+B followed by D), close the SSH and just walk away and do other things. You can tell your Pi is still busy by its activity led blinking like mad. Once it goes solid it means either the process is done (yay) OR something has gone horribly wrong (Frik). This can take a few days really...

If everything goes well you shouldn't have had any major errors. Only error is Python pleading to not use a deprecated easy_install method, but that can't be helped. Colcon will claim packages have failed because of this, but that isn't really the case. TMUX makes it hard to see if anything major happened (can't scroll up ) so it might be worthwhile to run colcon again in a normal session to verify.

IF you manage to do everything. Be sure to backup your card just in case.