Running Flatcar Container Linux on Raspberry Pi 4

Hardware Requirements

A Raspberry Pi 4
Form of storage, either USB and/or SD card. USB 3.0 drive is recommended for the better performance in terms of price.
Display (via micro HDMI/HDMI/Serial Cables)
Keyboard

Before we start

A word of warning:

The UEFI firmware used in this guide is an UNOFFICIAL firmware , provided under an open source BSD license.
Flatcar Container Linux support for Raspberry Pi is still in its early stages and is not thoroughly tested.
Deploy Flatcar Container Linux on the hardware for purely fun and learning.
Please follow the documentation at your own risk.

Update the EEPROM

The Raspberry PI 4 uses an EEPROM to boot the system. Before proceeding ahead, it is recommended to update the EEPROM. Raspberry Pi OS automatically updates the bootloader on system boot. In case you are using Raspberry Pi OS already, then the bootloader may be already updated.

For manually updating the EEPROM, you can either use the Raspberry Pi Imager or the raspi-config. The former is the recommended method in the Raspberry Pi documentation .

We will also see later how the RPi4 UEFI firmware needs a recent version of EEPROM.

Using the Raspberry Pi Imager (Recommended)

Install the Raspberry Pi Imager software. You can also look for the software in your distribution repository.
Launch Raspberry Pi Imager.
Select Misc utility images under Operating System.
Select Bootloader.
Select the boot-mode, SD, USB
Select the appropriate storage, SD or USB
Boot the Raspberry Pi with the new image and wait for at least 10 seconds.
The green activity LED will blink with a steady pattern and the HDMI display will be green on success.
Power off the Raspberry Pi and disconnect the storage.

Using the raspi-config

Update the rpi-eeprom package in the Raspberry Pi OS running.

sudo apt update
sudo apt full-upgrade
sudo apt install rpi-eeprom

Run sudo raspi-config
Select Advanced Options.
Select Bootloader Version
Select Latest for latest Stable Bootloader release.
Reboot

Using the rpi-eeprom-update

Update the rpi-eeprom package in the Raspberry Pi OS running.

sudo apt update
sudo apt full-upgrade
sudo apt install rpi-eeprom

Check if there are available updates.

sudo rpi-eeprom-update

Install the update

# The update is pulled from the `default` release channel.
# The other available channels are: latest and beta
# You can update the channel by updating the value of
# `FIRMWARE_RELEASE_STATUS` in the `/etc/default/rpi-eeprom-update`
# file. This is useful usually in case when you want
# features yet to be made available on the default channel.

# Install the update
sudo rpi-eeprom-update -a

# A reboot is needed to apply the update
# To cancel the update, you can use: sudo rpi-eeprom-update -r
sudo reboot

Installing Flatcar

Install `flatcar-install` script

Flatcar provides a simple installer script that helps install Flatcar Container Linux on the target disk. The script is available on Github , and the first step would be to install the script in the host system.

mkdir -p ~/.local/bin
# You may also add `PATH` export to your shell profile, i.e bashrc, zshrc etc.
export PATH=$PATH:$HOME/.local/bin

curl -LO https://raw.githubusercontent.com/flatcar/init/flatcar-master/bin/flatcar-install
chmod +x flatcar-install
mv flatcar-install ~/.local/bin

Install Flatcar on the target device

Now that the flatcar-install script is installed in the host machine, go ahead and install the Flatcar Container Linux image on the target device. The target device could be a USB drive or SD Card.

The options that we will be using with the scripts are:

# -d DEVICE   Install Flatcar Container Linux to the given device.
# -C CHANNEL  Release channel to use
# -B BOARD    Flatcar Container Linux Board to use
# -o OEM      OEM type to install (e.g. ami), using flatcar_production_<OEM>_image.bin.bz2
# -i IGNITION Insert an Ignition config to be executed on boot.

The device would be the target device that you would like to use. You can use the lsblk command to find the appropriate disk. For the example we would be using /dev/sda.
With the given values of channel and board, the script would download the image, verify it with gpg, and then copy it bit for bit to disk.
In our case, Flatcar does not yet ship Raspberry PI specific OEM images yet so the value will be an empty string ''.
Pass the Ignition file, config.json in my case, to provision the Pi during boot.

{
  "ignition": {
    "config": {},
    "security": {
      "tls": {}
    },
    "timeouts": {},
    "version": "2.3.0"
  },
  "networkd": {},
  "passwd": {
    "users": [
      {
        "name": "core",
        "sshAuthorizedKeys": [
          <Insert your SSH Keys here>
        ]
      }
    ]
  },
  "storage": {
    "files": [
      {
        "filesystem": "OEM",
        "path": "/grub.cfg",
        "append": true,
        "contents": {
          "source": "data:,set%20linux_console%3D%22console%3DttyAMA0%2C115200n8%20console%3Dtty1%22%0Aset%20linux_append%3D%22flatcar.autologin%20usbcore.autosuspend%3D-1%22%0A",
          "verification": {}
        },
        "mode": 420
      }
    ],
    "filesystems": [
      {
        "mount": {
          "device": "/dev/disk/by-label/OEM",
          "format": "btrfs"
        },
        "name": "OEM"
      }
    ]
  },
  "systemd": {}
}

Go ahead with the write on the target device

sudo flatcar-install -d /dev/sda -C stable -B arm64-usr -o '' -i config.json

If you already have the image downloaded you can use the -f param to specify the path of the local image file.

sudo flatcar-install -d /dev/sda -C stable -B arm64-usr -o '' -i config.json -f flatcar_production_image.bin.bz2

Raspberry Pi 4 UEFI Firmware

rpi-uefi community ships a SBBR-compliant(UEFI+ACPI), ArmServerReady ARM64 firmware for Raspberry Pi 4. We will be using it to UEFI boot Flatcar.

v1.17 of the pftf/RPi4 introduced two major changes:

Firstly, it enabled firmware boot directly from the USB. This is particularly helpful if you are using the installation process using a USB device.
Secondly, support for directly placing the Pi boot files into the EFI System Partition (ESP). This feature was not implemented in the firmware, rather from the upstream firmware from Raspberry Pi Foundation. This is why it is recommended to update the Pi EEPROM at the very beginning.

Let’s move ahead with the final steps.

Place the UEFI firmware into the EFI System Partition.

# Note `/dev/sda` mentioned in the example needs to be the USB drive that
# we installed flatcar onto
efipartition=$(lsblk /dev/sda -oLABEL,PATH | awk '$1 == "EFI-SYSTEM" {print $2}')
mkdir /tmp/efipartition
sudo mount ${efipartition} /tmp/efipartition
pushd /tmp/efipartition
version=$(curl --silent "https://api.github.com/repos/pftf/RPi4/releases/latest" | jq -r .tag_name)
sudo curl -LO https://github.com/pftf/RPi4/releases/download/${version}/RPi4_UEFI_Firmware_${version}.zip
sudo unzip RPi4_UEFI_Firmware_${version}.zip
sudo rm RPi4_UEFI_Firmware_${version}.zip
popd
sudo umount /tmp/efipartition

Remove the USB/SD from the host device and attach it into the Raspberry Pi 4 and boot.

In no time, your Raspberry Pi would boot and present you with a Flatcar Container Linux prompt.