Minimal Raspberry Pi 3 Linux configuration and Buildroot image

I was tired to get more than 100 MB of Linux modules by using the bcm2709 Linux kernel defconfig from the Raspberry Pi official Linux repository, so I have created a minimal Linux configuration for the Raspberry Pi 3 and then adapted Buildroot 2018.02-git to get an embedded system with a small footprint.

Result:

• Kernel: 2.4 MB
• Rootfs: 3.7 MB (651 kB for the kernel modules)

What do I have for that amount of bytes?

• Working HDMI + serial consoles
• Working Ethernet with DHCP
• Working internal Wifi with wpa_supplicant and DHCP
• A very simple GNU/Linux system that boots (from end of bootloader to start of init scripts) in 1.4 sec, you even have vi installed!

What is missing?

• Bluetooth
• Almost all modules, so you will have to had the ones you need
• GPU related stuff

How to use it?

Instead of making changes directly in Buildroot's tree, I have prepared a simple BR2_EXTERNAL which can live alongside mainline Buildroot.

Get Buildroot

Download or clone Buildroot in the parent directory

$ git clone git://git.buildroot.net/buildroot

Build the image

Create a new directory for the build (to keep the Buildroot tree clean), next to the freshly cloned buildroot directory

$ mkdir build

To avoid duplicates in the downloaded files, I recommend using a separate directory for the downloads, so create another directory buildroot_dl

$ mkdir buildroot_dl

Select your config

$ cd build
$ make BR2_EXTERNAL=../minimal_raspberrypi_buildroot/ O=$PWD -C ../buildroot/ raspberrypi3_minimal_defconfig

Then make

$ make

After a while, the SD card image is ready in images/sdcard.img, you can then flash it with dd or Etcher for example.

FAQ

• Why stripping everything to get a system barely functional? Just because we can
• Why using musl as C library? Just to give it a try
• Why not using "x, y" repository already available? Ah! interesting, I did not found it when I looked for it, please give me the URL to have a look
• I have tried you image and the system do not boot in 1.4 sec? This time was measured with the quiet argument given to the kernel, otherwise, the logs through the serial line slow down the boot. And by boot, I only mean the kernel boot, not the userspace (load network drivers then DHCP...)