Building Kubos Linux for the Pumpkin MBM2


This supplementary document covers specific features and components of Kubos Linux for the Pumpkin Motherboard Module 2.

The Kubos Linux Overview doc covers the major components of Kubos Linux.

Additionally, this document covers the steps required in order to build Kubos Linux.

Reference Documents

Pumpkin Documentation

The CubeSat Kit Motherboard Module (MBM) 2 reference document is available from Pumpkin and is a useful document for learning what each of the hardware components are and how they are connected.

Kubos Documentation

Software Components

ROM Bootloader

The ROM bootloader lives in a small section of ROM space. It should come pre-loaded on the board and should not need to be modified. It selects the next bootloader depending on whether the boot mode button is being held. If not held, it attempts to run the next boot step from eMMC storage; otherwise, it attempts to boot from the microSD card.


This board utilizes U-Boot’s SPL feature. A small boot file called “MLO” is run and that file then loads the main U-Boot image into SDRAM.

Kubos Linux Build Process

If for some reason you want or need to modify and rebuild the Kubos Linux components, follow the steps in this section.

Build the OS Files


The OS files cannot be built using a synced folder in a Vagrant box (or regular VM). VirtualBox does not support hard links in shared folders, which are crucial in order to complete the build.

SSH into a Kubos SDK box

In order to build Kubos Linux, two components are needed:

These components should be setup as children of the same parent directory. There are several commands and variables in the build process which use relative file paths to navigate between the components.

After the environment has been set up, all build commands will be run from the BuildRoot directory unless otherwise stated.

To set up a build environment and build Kubos Linux:

Create a new parent folder to contain the build environment

$ mkdir kubos-linux

Enter the new folder

$ cd kubos-linux

Download BuildRoot-2017.02 (more current versions of BuildRoot may work as well, but all testing has been done against 2017.02)


All Kubos documentation will refer to v2017.02.8, which is the latest version of the LTS release at the time of this writing.

$ wget && tar xvzf buildroot-2017.02.8.tar.gz && rm buildroot-2017.02.8.tar.gz

Pull the kubos-linux-build repo

$ git clone

Move into the buildroot directory

$ cd buildroot-2017.02.8

Point BuildRoot to the external kubos-linux-build folder and tell it to build for the Pumpkin MBM2.


You will need to build with sudo if you are using the default configuration, since it points the output toolchain to “/usr/bin/bbb_toolchain”, which is a protected directory.

$ sudo make BR2_EXTERNAL=../kubos-linux-build pumpkin-mbm2_defconfig

Build everything

$ sudo make

The full build process will take a while. Running on a Linux VM, it takes about an hour. Running in native Linux, it took about ten minutes. Once this build process has completed once, you can run other BuildRoot commands to rebuild only certain sections and it will go much more quickly (<5 min).

BuildRoot documentation can be found **here**

The generated files will be located in buildroot-2017.02.8/output/images. The relevant files are:

  • uboot.bin - The U-Boot binary
  • kernel - The compressed Linux kernel file
  • pumpkin-mbm2.dtb - The Device Tree Binary that Linux uses to configure itself for the Pumpkin MBM2 board
  • rootfs.tar - The root file system. Contains BusyBox and other libraries
  • kubos-linux.img - The complete Kubos Linux SD card image

Changing the Output Toolchain Directory (optional)

If you would like to build your toolchain in somewhere other than the “/usr/bin/bbb_toolchain” directory, update the BR2_HOST_DIR variable in the “configs/pumpkin-mbm2_defconfig” file.

If you would like BuildRoot to just build the toolchain locally, you may remove the BR2_HOST_DIR variable entirely. The toolchain will then be built under the main “buildroot-2017.02.8” directory in a new “output/host” folder.

Create auxilliary SD Card Image

By default, the build process will create a bootable SD card image. This will be flashed onto the eMMC. In order to create a full Kubos Linux setup, you’ll want to also create an auxiliary image for the microSD card containing the upgrade partition and an additional user data partition.

Follow the Upgrade Creation instructions in order to create a Kubos Package file (kpack-*.itb) to be used for recovery.

Then, from the kubos-linux-build/tools folder, run the format-aux.img script. This will create a new SD card image, aux-sd.img, with two partitions: - An upgrade partition containing kpack-base.itb - A user data partition

There are two parameters which may be specified:

  • -s : Sets the size of the aux-sd.img file, specified in MB. The default is 3800 (3.8GB)
  • -i : Specifies the name and location of the kpack-*.itb file to use as kpack-base.itb

For example:

$ ./ -i ../kpack-2017.07.21.itb