How to build Raspberry pi zero w BUILDROOT image

Lately I was reading about embedded linux and came to know about two such custom embedded linux system build sytem the Yocto project and Buildroot.I wanted to make my own custom linux for raspberyy pi zero W i had in my *ahem* attic.

Requirements:

1. Raspberry pi zero w (ofcourse)
2. A PC (with ubuntu 18.04 or higher)
3. microSD card
4. microSD card reader

Step 1: Preparing and downloading BUILDROOT

Open Ubuntu terminal (Ctrl+ALT+T) and type the below

$ wget https://www.buildroot.org/downloads/buildroot-2019.08.tar.gz
$ tar xvjf buildroot-2019.08.tar.gz
$ cd buildroot-2019.08

Building

Buildroot is now ready for initial configuration. There are few commands that can help:

$ make help
$ make list-defconfigs

output:

  raspberrypi0_defconfig              - Build for raspberrypi0
  raspberrypi0w_defconfig             - Build for raspberrypi0w
  raspberrypi2_defconfig              - Build for raspberrypi2
  raspberrypi3_64_defconfig           - Build for raspberrypi3_64
  raspberrypi3_defconfig              - Build for raspberrypi3
  raspberrypi3_qt5we_defconfig        - Build for raspberrypi3_qt5we
  raspberrypi4_defconfig              - Build for raspberrypi4

REAL FUN STARTS!

Type inside terminal

$ make raspberrypi0w_defconfig
$ make all

If there was no errors then continue editing the image to add wifi, bash , ssh, and whatever you need for your project.

$ make menuconfig

A small GUI pops up (should be in maximized terminal window), go through each sections . Use Y key to enable N to remove , press escape twice to go back or use exit option near the select option .

1. Target options –> leave it default
2. Build options –> select enable compiler cache
3. Toolchain –> Enable wchar support
4. System config -> change system hostname, system banner, root password , enable install timezone info
5. Hardware Handling

Hardware Handling -> Firmware -> rpi-wifi-firmware

6. Network applications

Networking applications -> wpa_supplicant
Networking applications -> wpa_supplicant - Enable 80211 support
Networking applications -> dropbear
Networking applications -> openssh

7. Target Packages -> Shell and utilities

Target Packages -> Shell and utilities ->bash

Also under System configuration -> under root password change shell to bash, also run getty login prompt after boot.

Finally

type the below code (fingers crossed!)

make all

once you get no error in output , output image files will be under

buildroot/output/images/

sdcardimage.img will be your image to burn to sdcard for Raspberry pi zero w.

Enabling Wi-Fi

In this subsection, we enable the Wi-Fi interface of the Raspberry Pi Zero W, so it will be able connect to any Wi-Fi networks.

wpa_supplicant

Create a file, named interfaces in buildroot/board/raspberrypi/ (all the other raspberrypi* are symlinks to this folder). The auto wlan0 will make sure that wlan0 is started when ifup -a is run, wich is done by the init scripts.

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp
    pre-up /etc/network/nfs_check
    wait-delay 15

auto wlan0
iface wlan0 inet dhcp
    pre-up wpa_supplicant -D nl80211 -i wlan0 -c /etc/wpa_supplicant.conf -B
    post-down killall -q wpa_supplicant
    wait-delay 15

iface default inet dhcp

Create another file, named wpa_supplicant.conf with wpa_passphrase in buildroot/board/raspberrypi/ (all the other raspberrypi* are symlinks to this folder). It should look like something like this:

ctrl_interface=/var/run/wpa_supplicant
ap_scan=1

network={
   ssid="EDIT_THIS"
   psk="EDIT_THIS"
}

ALSO

post-build.sh

The hotplug helper must be set as mdev and write /etc/mdev.conf file. The mdev package itself has some helper script for this and can be used directly. Also the above created files must be copied, so add the following lines to buildroot/board/raspberrypi/post-build.sh:

cp package/busybox/S10mdev ${TARGET_DIR}/etc/init.d/S10mdev
chmod 755 ${TARGET_DIR}/etc/init.d/S10mdev
cp package/busybox/mdev.conf ${TARGET_DIR}/etc/mdev.conf

cp board/raspberrypi/interfaces ${TARGET_DIR}/etc/network/interfaces
cp board/raspberrypi/wpa_supplicant.conf ${TARGET_DIR}/etc/wpa_supplicant.conf
cp board/raspberrypi/sshd_config ${TARGET_DIR}/etc/ssh/sshd_config

sshd config file

open/mount your sdimage.img file previously generated and copy /etc/ssh/sshd_config to buildroot/board/raspberrypi/ and add

PermitRootLogin yes
PermitEmptyPassword yes

One last ride

finally do

$ make all

you should have a fully working raspberry pi zero w linux custom image with ssh and wifi also you can add anything to this base build like wiringpi, gpio library, python etc even qt and xorg , keyboard support , mouse etc can be added.

CREDITS:

https://ltekieli.com/buildroot-with-raspberry-pi-what-where-and-how/

https://unix.stackexchange.com/questions/205271/sshd-not-starting-after-boot-on-embedded-linux-built-with-buildroot

https://blog.crysys.hu/2018/06/enabling-wifi-and-converting-the-raspberry-pi-into-a-wifi-ap/

https://unix.stackexchange.com/questions/396151/buildroot-zero-w-wireless