Flatcar Container Linux recently announced the Stable support for ARM64.

Perfectly timed! I had a Raspberry Pi 4 lying around and had just ordered a few more to set up a home lab during the holidays. The newer Pis are yet to arrive, so better utilize the time writing a walkthrough on how to use Flatcar Container Linux on your Pis.

Hardware Requirements

• Goes without saying, a Raspberry Pi 4
• Form of storage, either USB and/or SD card. USB 3.0 drive recommended because of the much better performance for the price.
• Display (via micro HDMI/HDMI/Serial Cables), keyboard

⚠️ WARNING ⚠️ The UEFI firmware used in this guide is an UNOFFICIAL firmware. There is a possibility of damage caused due to the usage of this firmware. The author of this article would not be liable for any damage caused. Please follow this article at your own risk.

Update the EEPROM

The Raspberry PI 4 use 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. Being a Fedora user I installed the software using dnf

dnf install rpi-imager

• 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.

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.

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-linux/init/flatcar-master/bin/flatcar-install
chmod +x flatcar-install
mv flatcar-install ~/.local/bin

Install Flatcar on the target device

Now that we have the flatcar-install installed in our host machine. We would go ahead and install the Flatcar Container Linux image on the target device. The target device could be a USB or SD Card. In my case, I reused the existing SD Card which I used in the previous steps. You can use a separate storage device as well.

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. Here, I’m using /dev/sda which was in my case.
• 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": {}
}

Write away!

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 would be using the same 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. To add a fun story, I dropped my Pi and broke the SD card slot. Until the Pi gets repaired, I’m making use of direct USB boot 😎
• 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.

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.

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

Further Reading

• rpi4-uefi.dev - RPi4 UEFI Firmware Official Website
• Raspberry Pi documentation

Photo by Anto Meneghini