RPI booted using only RAM

This is a way of running Raspberry PI 4B (RPI) which requires no SD-card (after setup). The RPI is booted over the network, and the full filesystem (which is created using SquashFS) is loaded into RAM over HTTP. Lastly, a OverlayFS is setup to enable seamless writing to the rootfs despite the SquashFS being read-only.

This setup is suitable for immutable/non-persistent infrastructure use-cases, such as kiosks, runners or similar. Out-of-the-box this repository includes a setup for running the RPI as a simple kiosk displaying a HTTP page, however this can be easily modified through the xinitrc script included.

This repo includes the setup to build and configure such a setup on an x86_64 system. This means that the RPI doesn't need to be used in the bootstrapping process, and enables this method to be easily used in a CI/CD pipeline.

This project uses the Rocky Linux Raspberry PI image maintained by SIG/Alt Arch as a base.

Build Requirements

• Some packages, including (but not limited to):
  • make
  • curl
  • squashfs-tools
  • qemu-user-static
  • qemu-user-static-binfmt
  • aarch64-linux-gnu-gcc
  • rpi-imager

Runtime Requirements

• SD card to run a one-time firmware update of the RPI.
• DHCP service which can supply Network boot/BOOTP configuration.
• TFTP service to serve the RPI firmware, initial RAM disk, and kernel.
• HTTP service to serve the squashed filesystem.

Setup

1. Prepare the RPI:
   1. Flash the SD card with rpi-imager, select utility and the 'Network boot' option (which tries to boot from the SD card first, and then from the network).
   2. Power the RPI with the SD card inserted, wait for the successful green screen.
   3. Then reboot the RPI without the SD card, and you should arrive at a startup screen where it shows that it tries to network boot. Note down the last 8 hex digits in the RPI serial number and MAC address.
2. Set the RPI_OSROOTFS environment variable to a reachable HTTP location from which the RPI will download the squashed root filesystem.
3. Run make to build rpi-rocky9-boot.tar.gz (the firmware, kernel and initramfs) and rpi-rocky9-rootfs.sq (the squashed root filesystem).
4. Unpack the *-boot.tar.gz file on the TFTP server in a folder with the same name as the RPI serial number from above. This must be a folder in the TFTP root (or if further customization is wanted of this location, a custom SD card must be made when flashing).
5. Move the *-rootfs.sq file to the HTTP server at the same location as the configured RPI_OSROOTFS environment variable.
6. Configure the DHCP server to provide at least the options vendor-class-identifier=PXEClient, tftp-server-name=<IP-address of TFTP server> and vendor-encapsulated-options="Raspberry Pi Boot " (NB! Last 3 spaces must be included). For example, the configuration for DHCPD might look like:
7. When the DHCP server starts serving these new config options, the RPI will eventually retry to boot across the network and now successfully do so.

# /etc/dhcp/dhcpd.conf

# ...

host <RPI hostname> {
    hardware ethernet <RPI MAC>;
    fixed-address <RPI IP-address>;
    next-server <IP-address of TFTP server>;

    option tftp-server-name "<IP-address of TFTP server>";
    option vendor-class-identifier "PXEClient";
    option vendor-encapsulated-options "Raspberry Pi Boot   ";
}