[Boot-BBB] 5. Create a Beaglebone Black image with Buildroot

Translated from the Vietnamese original; wording may still be rough. Read the original →

In this post I show you how to use Buildroot to create a Beaglebone Black image. Simply put, Buildroot is similar to the Yocto Project but leaner, with less configuration. The end goal is to build a custom embedded linux image

1. Clone the source code

bash

git clone https://git.buildroot.net/buildroot

We checkout the latest build version

bash

cd buildroot
git branch -a

Scroll to the bottom; mine is branch remotes/origin/2025.08.x, so I checkout this branch

bash

git checkout 2025.08

2. Configure Buildroot

bash

make menuconfig

Following the bootlin buildroot labs

We choose the following configuration

Target Options
- Target Architecture
  - Arm little endian
- Target Architecture Variant
  - cortex-A8
Toolchain
- Toolchain type
  - External toolchain
System Configuration (these settings are up to you)
- System hostname
  - beaglebone
- System banner
  - Zk47's Buildroot Image
- Enable root login
  - Root password
    - test
Kernel
- Linux Kernel
  - *
- Defconfig name
  - omap2plus
- Kernel binary format
  - zImage
- Build a Device Tree Blob (DTB), see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/ti/omap?id=v6.9
  - *
    - In-tree Device-Tree Source file name
      - ti/omap/am335x-boneblack

Target Packages: remember to enable Busybox; beyond that you can add gdb, valgrind, dropbear, or even games
Bootloader
- U-boot
  - *
  - Board defconfig
    - am335x_evm
  - U-boot binary format
    - Enable only u-boot.img

3. Build buildroot

bash

make 2>&1 | tee build.log

After running for a while I got an error

bash

tools/mkeficapsule.c:20:10: fatal error: gnutls/gnutls.h: No such file or directory
   20 | #include
      |          ^~~~~~~~~~~~~~~~~
compilation terminated.
make[3]: *** [scripts/Makefile.host:112:

This error is similar to the openssl error in post 4; I am simply missing the needed libraries and packages.

Again I searched google with the keyword Buildroot prerequisites. And here are all the needed packages, better too many than too few :vv

bash

sudo apt-get update && sudo apt-get install -y \
  build-essential git wget curl cpio unzip rsync file bc \
  bison flex gawk texinfo \
  libssl-dev libgnutls28-dev uuid-dev \
  libncurses5-dev libncursesw5-dev \
  libglib2.0-dev libpixman-1-dev \
  python3 python3-matplotlib \
  asciidoc w3m dblatex graphviz \
  patch diffutils perl sed tar gzip bzip2 findutils make binutils

The make takes quite long because it both fetches the kernel source code and builds. It took about 40 minutes on my machine

Okay, once the build is done, the results are in output/images

bash

zk47@ltu:~/Learning/Bootlin_practice/buildroot/output/images$ ls
am335x-boneblack.dtb  MLO  rootfs.tar  u-boot.img  zImage

Exactly like posts 2 and 3

Replace the MLO, u-boot.img, zImage and am335x-boneblack.dtb files on the boot partition of the SD card

Then wipe the rootfs partition and extract rootfs.tar into it

cpp
sudo umount /dev/mmcblk0p2
sudo mkfs.ext4 -L rootfs /dev/mmcblk0p2

I clear this partition first, then extract into it

bash

sudo tar -C /media/$USER/rootfs/ -xf rootfs.tar
sync

Okay, let's test again on the board

bash

[    4.019342] VFS: Mounted root (ext4 filesystem) on device 179:2.
[    4.025955] devtmpfs: mounted
[    4.033920] Freeing unused kernel image (initmem) memory: 2048K
[    4.041332] Run /sbin/init as init process
[    4.292822] EXT4-fs (mmcblk0p2): re-mounted 2977d641-4bac-4ed7-89c4-e22fbc9812e3 r/w. Quota mode: disabled.
Saving 256 bits of creditable seed for next boot
Starting syslogd: OK
Starting klogd: OK
Running sysctl: OK
Starting network: OK
Starting crond: OK

Zk47's buildroot image
bbb login: test
Password:
Login incorrect
bbb login: root
Password:
# ls
# ls
# which cat
/bin/cat
# ls -al /bin/cat
lrwxrwxrwx    1 root     root             7 Sep 21  2025 /bin/cat -> busybox