Setting Up Lots of Raspberry Pis

I help out with a STEM club aiming to teach Sixth Form students skills in Cyber Security and other up and coming tech that doesn't normally get taught in school. I actually used to be in the same club when I was younger so it's nice to go full circle and help out there!

As part of the club, we need some computers for the students to work on. We managed to find around ten Raspberry Pi 400 computers which we are going to trail for a few sessions. Unfortunately, they are underpowered when compared to a modern laptop but hopefully they'll work well enough for some simple web browsing, Linux command line and other stuff. In cases we want more power, we might look to use cloud alongside these Raspberry Pis.

Initial Tests

To start, I initially booted up one Pi 400 with it's existing SD card to get a feel for how web browsing would perform, as well as some other simple tasks. I've personally not used the Raspberry Pi OS Desktop for ages, and tend to just go for the Lite versions with no GUI. Unfortunately, web browsing was pretty sluggish with frequent freezes and slow load times.

To speed things up, I tried a 64-bit image which supposedly improves speed (especially for systems with >4GB RAM). Maybe the original image was 32-bit, or a fresh install did the job, but thankfully this improved web browsing to the point it would work for our purposes. I also experimented with a very small overclock to squeeze a little more speed out, going from 1.8 GHz to 2.0 GHz. After that, it now performs fine.

Setting them up

The default Raspberry Pi OS comes with an initial setup wizard, which is great if you're setting up 1, but means that I need to go through this wizard 10 times on each of the Pis. Doable, but I'd rather automate it a little more.

My next thought was to write a Rubber Ducky script for my Flipper Zero to automate going through the setup wizard and any other steps we want (e.g. making a non-sudo student account, installing additional software, etc...). It would be a little error prone as it's not able to get feedback from the OS, but it would have been a good solution.

Eventually, I decided to try and make my own image that we could use in the future for any stuff. I found a couple of tools that did this from HashiCorp Packer, ARM builder, to a purpose built tool called sdm. I tried the Packer builder but the image it made didn't end up booting. I'm sure it's something I had missed but I didn't have the time to troubleshoot, so I tried sdm instead.

sdm works really well and each option is configured using a command line argument. For example, creating a user just needs the argument --plugin user:"adduser=student|password=student|nosudo". You can also do some fancy things like copying files locally (e.g. config files) to specific places in the image.

To save what I had done, I made a very simple script to generate the image:

#!/bin/bash
if [[ $EUID -ne 0 ]]; then
        echo "This script must be run as root" 1>&2
        exit 1
fi

ADMIN_PASSWORD="password"

sdm --customize $1 \
        --plugin user:"deluser=pi" \
        --plugin user:"adduser=student|password=student|nosudo" \
        --plugin user:"adduser=admin|password=${ADMIN_PASSWORD}" \
        --plugin raspiconfig:"boot_behaviour=B4" \
        --plugin disables:piwiz \
        --plugin bootconfig:"arm_freq=2000|over_voltage=6" \
        --plugin wificonfig:"country=GB" \
        --plugin L10n:"keymap=gb|locale=en_GB.UTF-8|timezone=Europe/London" \
        --plugin network:"ssh=service" \
        --plugin copyfile:"from=authorized_keys|to=/home/admin/.ssh/|chown=admin:admin|chmod=600|runphase=postinstall|mkdirif" \
        --plugin copyfile:"from=lightdm.conf|to=/etc/lightdm/|chown=root:root|chmod=644|runphase=postinstall" \
        --plugin copyfile:"from=05-setup.sh|to=/etc/sdm/0piboot/|chown=root:root|chmod=744|runphase=postinstall" \
        --restart --bootscripts

The above command does the following (in order):

• Delete's the default pi user (although I don't think it actually exists anymore, so this may be redundant).
• Adds an admin and non-sudo student users.
• Sets the boot behaviour to auto-login to the desktop (as opposed to going to the console, or just going to the desktop).
• Disables the setup wizard (piwiz).
• Applies the overclock to /boot/config.txt.
• Sets the Wi-Fi region, keyboard, locale and timezone to the UK.
• Enable SSH - for any bulk setting up later on (e.g. with Ansible).
• Copy my SSH key to the relevant location so I can login over SSH without a password.
• Copy the lightdm.conf file which is setup to automatically login the student user.
• A custom script to set the hostname to a random value.

This image worked like a charm, helping save me from lots of setup, and it'll be a great base to build off in the future.

What's next?

If all goes well, my plan is to implement PiServer, a network boot server where each Pi is a thin-client. This means all the users and their data are in one central location. I think this will make it much easier to add new software, distribute files, etc... further down the line. At the moment each Pi would have to be configured individually for anything like that.