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LinuxKit on a Raspberry Pi 3b

LinuxKit supports building and booting images on a Raspberry Pi 3b using the mainline arm64 bit kernels. The LinuxKit arm64 kernel has support for some of the devices on the Raspberry Pi 3b and 4, but notably it does not support:

  • WLAN
  • Bluetooth
  • Graphics (though text console should work)

It is unlikely, that we going to add support for these in the main LinuxKit kernels in the near future. The LinuxKit kernel is more targeted at VMs and baremetal servers where support for these type of devices is typically not needed. However, it should be possible to easily extend the LinuxKit kernel build process add the required kernel options, in a similar fashion to how -dbg kernels are build. See the kernel documentation for details.

Boot

We use the mainline Linux kernels for the Raspberry Pi and it is booted via uboot. The moby tool, via linuxkit build -format rpi <YAML>, currently produces a tar archive which can be extracted onto a FAT32 formatted SD card to boot your Raspberry Pi.

Currently, the root filesystem is provided as a RAM disk via the initrd.

Console

The LinuxKit images support console access via HDMI and USB keyboard as well as via serial. For serial console, you need a suitable cable to connect to the GPIO pins as described here.

Disks

SD Card

The built in SD Card is supported

For Raspberry Pi 4b use:

  - name: block
    image: linuxkit/modprobe:v0.8
    command: ["modprobe", "mmc_block" ]
  - name: sdhci
    image: linuxkit/modprobe:v0.8
    command: ["modprobe", "sdhci-iproc" ]

USB Sticks

To enable and external USB stick as disk, add the following to the onboot section in your YAML:

  - name: usb-storage
    image: linuxkit/modprobe:<hash>
    command: ["modprobe", "usb_storage"]

Networking

The onboard, USB connected network interface is supported by the LinuxKit kernel, but for some unknown reason the driver is not cold plugged by mdev. To use the network interface, the driver needs to be modprobed before the network interface can be used. The easiest way is to add the following section to the onboot section in your LinuxKit YAML file:

  - name: netdev
    image: linuxkit/modprobe:<hash>
    command: ["modprobe", "smsc95xx"]

For Raspberry Pi 3b+ use:

  - name: netdev
    image: linuxkit/modprobe:<hash>
    command: ["modprobe", "lan78xx"]

For Raspberry Pi 4b use:

  - name: netdev
    image: linuxkit/modprobe:v0.8
    command: ["modprobe", "mdio-bcm-unimac" ]
  - name: netdev
    image: linuxkit/modprobe:v0.8
    command: ["modprobe", "bcm7xxx" ]

Examples

TODO: Figure out why mdev is not loading the driver.