Modifying kernel sources on BeagleBone Black made simple. Follow 7 proven steps to customize, optimize, safely build your own powerful Linux
When you first hear the phrase “modifying kernel sources”, it can sound like rocket science. But here’s the truth: if you’re working in embedded systems, Linux development, or system programming, learning how to tweak the kernel is an important step in becoming a stronger developer.
The Linux kernel isn’t just another piece of software—it’s the brain of your operating system. It decides how memory is allocated, how hardware talks to software, and how processes communicate with each other. Sometimes, you may want to modify kernel sources to:
- Add support for new hardware (like a custom driver).
- Optimize system performance.
- Fix bugs or apply patches.
- Experiment and learn deeper system internals.
Let’s break this down in a beginner-friendly way.
What Does “Modifying Kernel Sources” Mean?
Think of the kernel as the engine of a car. If you want to improve mileage or add turbo boost, you open up the engine and tweak it. Similarly, when we talk about modifying kernel sources, we mean changing the kernel’s codebase (written mainly in C and assembly) to add or adjust functionality.
The kernel source is freely available (thanks to open source), which means you can download it, configure it, edit it, and then rebuild it into your system.
Steps to Modify Kernel Sources
1. Get the Kernel Source Code
You can download the Linux kernel from the official website kernel.org or use your Linux distribution’s source package.
# Example: Ubuntu
sudo apt-get source linux-image-$(uname -r)
2. Set Up a Build Environment
Install the required tools:
sudo apt-get install build-essential libncurses-dev bison flex libssl-dev
This ensures you have compilers and dependencies to build the kernel.
3. Configure the Kernel
Before making modifications, configure your kernel. Run:
make menuconfig
This opens a simple text-based UI to enable/disable features and drivers.
4. Modify the Source Code
Now comes the fun part! Let’s say you want to print a custom message whenever the kernel boots. You could edit the init/main.c file and add a simple printk("Hello from my custom kernel!\n");.
5. Build and Install the Kernel
Compile your kernel:
make -j$(nproc)
sudo make modules_install
sudo make install
Then update your bootloader (GRUB) and reboot into your shiny new modified kernel.
Best Practices for Modifying Kernel Sources
- Keep Backups – Always keep a backup of your working kernel. A small mistake can lead to a system crash.
- Work on Virtual Machines – If you’re a beginner, use VirtualBox or QEMU to avoid bricking your real system.
- Use Version Control (Git) – Track your changes so you can roll back when needed.
- Start Small – Add a printk message, modify a driver, or tweak configuration options before jumping into complex changes.
Why Modifying Kernel Sources Matters
- For Embedded Developers: Custom hardware often needs custom drivers, which means kernel modification.
- For Performance Enthusiasts: You can optimize the kernel to run faster on your specific hardware.
- For Learners: Nothing teaches you systems programming better than reading and modifying kernel code.
Real-World Example
Suppose you’re building an IoT device with a custom sensor. Out of the box, Linux won’t know how to talk to it. By writing a driver and integrating it into the kernel sources, you make the OS aware of your hardware. That’s the power of kernel modification!
If you’re curious about taking this further into a full build system workflow, check out my beginner-friendly guide on Hello World using Yocto — it’s a great way to see how kernel-level changes fit into a complete embedded Linux image.
TL;DR — what you’ll do
- Prepare a Linux host (install toolchain & build tools). (itdev.co.uk)
- Get a BBB-friendly kernel source (mainline or TI/BBB patched tree). (docs.beagleboard.org)
- Configure (use the BBB defconfig), edit code you want, then cross-compile (
ARCH=arm CROSS_COMPILE=...). (modbus.pl) - Build zImage / dtbs / modules, copy them to an SD card or install .deb packages on the BBB, update
uEnv.txt, and boot. (DESE Labs |) - Test via serial console (115200 8N1), debug logs, iterate. (Dummies)
Step by step guide to modify, build and deploy a Linux kernel for the BeagleBone Black
Safety first: always test on a microSD card before writing to eMMC. Backup anything important on the board. Many guides recommend building and deploying to SD first. (DESE Labs |)
0) Prepare a host machine (Ubuntu/Debian recommended)
sudo apt update
sudo apt install -y git build-essential bc bison flex libssl-dev \
libncurses-dev u-boot-tools device-tree-compiler \
gcc-arm-linux-gnueabihf crossbuild-essential-armhf
(That set installs compilers, DTC, u-boot tools and the ARM cross toolchain.) (itdev.co.uk)
1) Create a workspace and grab kernel sources
You can use mainline kernel from kernel.org or a BBB/TI patched tree (Robert C. Nelson’s / ti kernels are popular for BBB work because they include device-tree and helper scripts).
Example (RobertCNelson BBB dev repo):
mkdir -p ~/bbb-work
cd ~/bbb-work
git clone --depth=1 https://github.com/RobertCNelson/ti-linux-kernel-dev.git
# or the beagleboard kernel:
# git clone --depth=1 https://github.com/beagleboard/linux.git
cd ti-linux-kernel-dev
(Choose the repo/version that matches your rootfs or target kernel series.) (embeded.readthedocs.io)
2) Export build env (important)
export ARCH=arm
export CROSS_COMPILE=arm-linux-gnueabihf-
Use those env vars for every make so the host builds for ARM/BBB. (modbus.pl)
3) Use a BeagleBone defconfig and tweak
Common BBB defconfigs: am335x_evm_defconfig or bb.org_defconfig depending on tree.
cd linux # kernel source dir
make ARCH=arm CROSS_COMPILE=${CROSS_COMPILE} am335x_evm_defconfig
# tweak:
make ARCH=arm CROSS_COMPILE=${CROSS_COMPILE} menuconfig
Start small: enable features you need (drivers, debug printk) and leave everything else default until you’re comfortable. (DESE Labs |)
4) Build kernel, device-trees (DTBs), and modules
# Build kernel image, DTBs and modules
make -j$(nproc) ARCH=arm CROSS_COMPILE=${CROSS_COMPILE} zImage dtbs modules
# Or build everything (zImage, modules, dtbs):
make -j$(nproc) ARCH=arm CROSS_COMPILE=${CROSS_COMPILE}
You’ll find: arch/arm/boot/zImage and device trees under arch/arm/boot/dts/*.dtb. (modbus.pl)
5) Install kernel modules into a rootfs (SD card mount or deploy dir)
If you prepared a mounted SD rootfs at /media/rootfs:
make ARCH=arm CROSS_COMPILE=${CROSS_COMPILE} INSTALL_MOD_STRIP=1 \
INSTALL_MOD_PATH=/media/rootfs modules_install
This places /lib/modules/ on the target filesystem. (DESE Labs)
6) Copy kernel image, DTB and update uEnv.txt (deploy to SD card)
On a typical Debian BBB image you copy the kernel and dtb into /boot on the rootfs or onto the boot partition, and set uname_r in /boot/uEnv.txt to tell U-Boot which kernel to load.
Example (when /media/rootfs is your mounted SD root):
kernel_version=5.x.y-yourtag
sudo cp arch/arm/boot/zImage /media/rootfs/boot/vmlinuz-${kernel_version}
sudo mkdir -p /media/rootfs/boot/dtbs/${kernel_version}
sudo cp arch/arm/boot/dts/am335x-boneblack.dtb /media/rootfs/boot/dtbs/${kernel_version}/
# Add entry to uEnv.txt
echo "uname_r=${kernel_version}" | sudo tee -a /media/rootfs/boot/uEnv.txt
Many community scripts produce .deb packages to make this safer — installing linux-image*.deb on the board is often simpler. (DESE Labs |)
7) Flash u-boot (if you’re creating a full SD image) — optional
If you’re making a bootable SD from scratch you may need to write MLO and u-boot.img to the card with dd. Be careful — picking the wrong device will destroy disks.
Example from guides:
sudo dd if=./u-boot/MLO of=/dev/sdX bs=128k seek=1
sudo dd if=./u-boot/u-boot.img of=/dev/sdX bs=384k seek=1
(Only needed if building a complete SD image; if you’re using a stock Debian SD and just replacing the kernel, you don’t need this.) (DESE Labs |)
8) Boot & test via serial console
Connect to the BBB serial console (either USB serial /dev/ttyACM0 or an FTDI to the J1 header). Default serial settings: 115200 8N1. Use screen or minicom:
screen /dev/ttyACM0 115200
# or
minicom -D /dev/ttyUSB0 -b 115200
Power on the board and watch the U-Boot + kernel boot messages to confirm your kernel loaded. (Dummies)
Helpful hints & troubleshooting
- Always test on SD — if boot fails you can remove the SD and revert to eMMC. (DESE Labs |)
- If the board doesn’t boot: double-check
uEnv.txtuname_rentry or thatzImageand the*.dtbare in the right location. Many boot failures are due to wrong dtb or wrong file paths. (BeagleBoard) - If modules don’t load, ensure
/lib/modules/was installed on the target filesystem. (DESE Labs |) - Want a simpler workflow? Use the RobertCNelson build scripts which produce
.debfiles you canscpanddpkg -ion the BBB — that avoids manual file placement. (embeded.readthedocs.io)
Quick checklist before you build
- Host packages and cross compiler installed. (itdev.co.uk)
- Kernel source and appropriate defconfig (am335x_evm_defconfig / bb.org_defconfig). (DESE Labs |)
ARCH=armandCROSS_COMPILE=arm-linux-gnueabihf-exported. (modbus.pl)- Test on SD, use serial console to view boot logs. (DESE Labs |)
Useful references (read more)
- BeagleBoard Cookbook — kernel chapter (good conceptual guide). (docs.beagleboard.org)
- Cross-compiling how-tos and step scripts / lab guides (examples show exact
make/dd/copy steps). (DESE Labs |) - RobertCNelson / Debian-style BBB kernel build & deploy (makes life easier — creates .deb packages). (embeded.readthedocs.io)
Final Thoughts
Modifying kernel sources may feel intimidating at first, but once you start, you’ll realize it’s just like tinkering with any other software project—only more powerful. It gives you control, flexibility, and deep understanding of how operating systems really work.
So, if you’re curious about Linux kernel development, don’t hesitate—download the source, make small edits, and experiment. Who knows, your first change might just be the beginning of your journey into system-level programming mastery.
FAQ: Modifying Kernel Sources on BeagleBone Black
1. Why would I want to modify the kernel on BeagleBone Black?
You may need to modify the kernel if you want to:
- Add support for new hardware (e.g., a custom sensor or driver).
- Optimize performance for embedded projects.
- Fix bugs or apply patches.
- Learn deeper system-level programming and Linux internals.
2. Do I need special hardware to build the kernel for BBB?
No. You can cross-compile the kernel from a normal Linux PC or laptop using an ARM toolchain. The only hardware you need is the BeagleBone Black board itself and a microSD card for testing.
3. Can I build the kernel directly on the BeagleBone Black?
Yes, but it’s not recommended. The BeagleBone Black has limited CPU and RAM, so compiling a full Linux kernel will take hours. Cross-compiling on a powerful host PC is much faster.
4. Where can I get the kernel sources for BeagleBone Black?
You can:
- Download the mainline Linux kernel from kernel.org.
- Use BeagleBoard’s official GitHub repository (includes patches for BBB).
- Use Robert C. Nelson’s ti-linux-kernel-dev repo, which comes with handy build scripts.
5. What is the correct kernel configuration for BBB?
For BeagleBone Black, common default configurations are:
am335x_evm_defconfig(generic TI AM335x boards).bb.org_defconfig(BeagleBoard.org maintained configs).
6. How do I test my custom kernel safely?
The safest way is to boot your new kernel from a microSD card. If the kernel fails, you can simply remove the SD card and boot the default eMMC image. Never overwrite your eMMC until your kernel is stable.
7. What happens if my modified kernel doesn’t boot?
Don’t panic 🙂. Use the serial console to check boot logs. Common causes are:
- Wrong device tree (
dtb) file. - Missing kernel modules.
- Incorrect
uname_rentry inuEnv.txt.
Since you tested on SD card, just revert back and try again.
8. Do I need to recompile the entire kernel for small changes?
Not always. For minor tweaks (like changing drivers), you may only need to rebuild affected modules. But for bigger changes (e.g., editing core kernel code), a full rebuild is required.
9. Can I use Yocto or Buildroot for BeagleBone Black kernel builds?
Yes. Many developers use Yocto or Buildroot for production images because they provide more control and automation. But for learning and experimentation, manual cross-compilation is simpler.
10. Is modifying the kernel safe for my board?
Yes, as long as you:
- Work on an SD card first (not eMMC).
- Keep backups of your working kernel.
- Make incremental changes instead of big jumps.
Mr. Raj Kumar is a highly experienced Technical Content Engineer with 7 years of dedicated expertise in the intricate field of embedded systems. At Embedded Prep, Raj is at the forefront of creating and curating high-quality technical content designed to educate and empower aspiring and seasoned professionals in the embedded domain.
Throughout his career, Raj has honed a unique skill set that bridges the gap between deep technical understanding and effective communication. His work encompasses a wide range of educational materials, including in-depth tutorials, practical guides, course modules, and insightful articles focused on embedded hardware and software solutions. He possesses a strong grasp of embedded architectures, microcontrollers, real-time operating systems (RTOS), firmware development, and various communication protocols relevant to the embedded industry.
Raj is adept at collaborating closely with subject matter experts, engineers, and instructional designers to ensure the accuracy, completeness, and pedagogical effectiveness of the content. His meticulous attention to detail and commitment to clarity are instrumental in transforming complex embedded concepts into easily digestible and engaging learning experiences. At Embedded Prep, he plays a crucial role in building a robust knowledge base that helps learners master the complexities of embedded technologies.
