hkn gravatar image

Posted 2015-04-09 17:06:37 +0100


Building kernel for RPi2 with bluetooth_6lowpan for Raspbian

Building kernel for RPi2 with bluetooth_6lowpan

In this guide, you will have two choices:

  • Cross-compilation build

  • Native build

Choose the one that fits your needs. Cross-compilation is the fastest choice.


In addition to the already installed tools in Raspbian, you'll need

  • Git
  • kernel-package

These can be installed using apt:

sudo apt-get install git kernel-package -y

“kernel-package” is needed for generating the .deb package, and git is used to fetch the repository from Raspberry Pi’s github account. We'll fetch the default branch, which holds 3.18.11 at the time of writing this blog post.

Obtaining the kernel

Open a terminal and maneuver to a clean directory, I made a directory ~/raspbian.

Now we need to clone the kernel:

git clone

Grab a coffee. This will take a while.

Option 1: Cross-compilation on x86/x64

The easiest option is to grab the toolchain from RaspberryPi. Go into a clean directory and clone:

git clone

Now we’ll have to define this path for easier building. For building on x86 (32-bit) environment:

export CCPREFIX=/path/to/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/bin/arm-linux-gnueabihf-

For building on x64 (64-bit) environment:

export CCPREFIX=/path/to/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-

Go to the kernel directory that you just cloned. We’ll have to ensure that the directory is cleaned

hkn@hkn-VirtualBox:~/raspbian/kernel/linux$ make mrproper

Set the default configuration to bcm2709, which is the chipset for Raspberry Pi 2

hkn@hkn-VirtualBox:~/raspbian/kernel/linux$ ARCH=arm CROSS_COMPILE=${CCPREFIX}
 make bcm2709_defconfig

Now we’ll start compiling

hkn@hkn-VirtualBox:~/raspbian/kernel/linux$ ARCH=arm CROSS_COMPILE=${CCPREFIX} INSTALL_MOD_PATH=${MODULES_TEMP} make –j5

hkn@hkn-VirtualBox:~/raspbian/kernel/linux$ ARCH=arm CROSS_COMPILE=${CCPREFIX} INSTALL_MOD_PATH=${MODULES_TEMP} make –j5 modules

On multi-core CPUs, you can utilize the cores via the “-j” operation. On my PC, I have 4 cores, therefore I add “-j 5” to the above command to speed things up. You should set the number to “NUM_OF_CPU_CORES + 1” to ensure that your cores are working full-time.  

Option 2: Native build

It’s recommended to have 10 GB free space on your Raspberry for kernel compilation.

The steps here are very similar to the section about cross-compilation, just that we remove a couple of defines.

First we need to ensure that you have your build essentials in order:

pi@raspberry:~/$ sudo apt-get install build-essential –y

Set the default configuration to bcm2709, which is the chipset for Raspberry Pi 2

pi@raspberry:~/raspbian/kernel/linux$ make bcm2709_defconfig

Now we’ll start compiling

pi@raspberry:~/raspbian/kernel/linux$ make –j5 && make –j5 modules

Generate .deb packages

For cross-compilation approach:

hkn@hkn-VirtualBox:~/raspbian/kernel/linux$ CONCURRENCY_LEVEL=5 DEB_HOST_ARCH=armhf fakeroot make-kpkg --append-to-version –name_of_your_choice --revision `date +%Y%m%d%H%M%S` --ARCH=arm --cross-compile ${CCPREFIX} kernel_image kernel_headers

CONCURRENCY_LEVEL sets the number of jobs. I used 5 since I have four CPU cores.

You will see warnings similar to this when generating the .deb files:

dpkg-architecture: warning: specified GNU system type arm-linux-gnu does not match gcc system type x86_64-linux-gnu, try setting a correct CC environment variable

Don’t worry; this is normal when cross-compiling, and actually reassuring that we did compile the kernel for ARM architecture.

For native build approach:

pi@raspberry:~/raspbian/kernel/linux$ CONCURRENCY_LEVEL=5 DEB_HOST_ARCH=armhf fakeroot make-kpkg --append-to-version –name_of_your_choice --revision `date +%Y%m%d%H%M%S` --initrd kernel_image kernel_headers

The .deb files will be placed in the parent directory. Write “ls ../*.deb” and you should have two files:


Installing the kernel on your Raspberry Pi 2

If you cross-compiled, you’ll need to transfer your kernel header and kernel image to the Pi. This can be done via scp for instance.

scp linux-header*.deb linux-image*.deb pi@pi-ip:~

This will transfer the files to your home directory.

Now login to your raspberry pi and update your system, and install the new kernel:

sudo dpkg –i linux-header*.deb linux-image*.deb

The kernel is now installed, but we need to specify in our boot settings that it should use this new kernel.

pi@raspberry ~ $ cd /boot
pi@raspberry /boot $ ls | grep vmlinuz

Here we found the name of our new kernel image. For simplicity, we will make a symbolic link (shortcut) to ‘vmlinuz’:

pi@raspberry /boot $ sudo ln –s vmlinuz-3.18.11-rpi2-v7+ vmlinuz

Now we specify the kernel and append it to config.txt:

pi@raspberry /boot $ sudo sh –c ‘echo “kernel=vmlinuz” >> config.txt’

Reboot and enjoy a fresh new kernel with the bluetooth_6lowpan module.


ZOU gravatar image

Posted May 1, 2015, 3:57 a.m.

Hi Hakon,

Thanks for the great guide. I managed to get a RPi2 then tried the steps. My setup is Raspbian 2015-02-16 on R.Pi 2 Model B, with a 16G microSD.

For the cross-compilation, I build the Raspbian kernel on my Ubuntu 15.4 laptop. But the kernel has a dependency on libc6 (>= 2.14), while the Raspbian host has 2.13-38+rpi2+deb7u8, so cannot install the debian package.

For the native build, it works. Major steps that I did

Get git, bc and kernel-package

sudo apt-get install git bc kernel-package -y

Clone the kernel (3.18.12 at the time that I fetched)

git clone

Get build essential

sudo apt-get install build-essential –y

Set default configuration

make bcm2709_defconfig


make –j 5 && make –j 5 modules

Dedian package

CONCURRENCY_LEVEL=5 DEB_HOST_ARCH=armhf fakeroot make-kpkg --revision date +%Y%m%d --initrd kernel_image kernel_headers

I successfuly created two debian files of

linux-headers-3.18.12-v7+_20150501_armhf.deb and linux-image-3.18.12-v7+_20150501_armhf.deb

This image has dependency on libc6 (>= 2.13-28), which is all fine. After install it, bluetooth_6lowpan is present.

BR, zou

hkn gravatar image

Posted May 6, 2015, 9:26 p.m.

Hi Zou,

I'm glad to hear that the guide was useful! Regarding the dependency to libc6 when cross-compiling; This is something I also saw when running Ubuntu 15.04-AMD64, but I did a force install to verify that the kernel booted properly on the RPi2. The problem seems to be that Ubuntu 15.04 seems to set a dependency to the systems libc instead of the crosscompiled targets libc when it's creating the debian packet using make-kpkg.

I also did a successful deb-generation on Ubuntu 14.10, and figured it was a 15.04-issue (at the time of writing the blog, 15.04 was still in beta), but it might also be that the "make-kpkg" is called incorrectly from my side.

It's an annoying issue, but it's not due to cross-compiling, but rather the generation of the .deb files.

I haven't been able to get around this in 15.04 (yet).

Cheers, Håkon

Posted May 21, 2015, 11:23 p.m.

Hi Zou and Håkon,

I followed Zou's instructions to build a new kernel on my Raspberry Pi 2.

First, I did not need the build-essential and git packages. They were already installed on 2015-05-05-raspbian-wheezy.img.

Second, make –j 5 && make –j 5 modules gave an error, saying make does not know how to make target -j5 (this was bizarre, because man page says -j is an option. Further, I tried --jobs=5 and it did go thru, but only 1 job at a time. So, it is still building (2+ hours, now)

Any comments?


horiebin gravatar image

Posted June 18, 2015, 9:58 p.m.

Hello Hakon

I tried the cross-compiling the kernel for my raspberry pi 2 on my Ubuntu 14.04. I followed your guide and found a problem when doing "Generate .deb packages". It appeared a problem which was caused by a bug of My version of ubuntu.And fixed it by downloading this package .

However, the debian files I have created had the same problem with Zou. So now I need to take hours to do the native build.

horiebin gravatar image

Posted June 20, 2015, 11:33 p.m.

When I tried the native-build on my raspberry-pi-2 with 16G sd card I meeted a problem :

WARNING: missing /lib/modules/3.18.16-rpi2-6lowpan-v7+ Device driver support needs thus be built-in linux image!

ERROR: could not open directory /lib/modules/3.18.16-rpi2-6lowpan-v7+: No such file or directory FATAL: could not search modules: No such file or directory

ERROR: object '' from LD_PRELOAD cannot be preloaded: ignored.

WARNING: could not open /var/tmp/mkinitramfs_kQya3Z/lib/modules/3.18.16-rpi2-6lo wpan-v7+/modules.order: No such file or directory

WARNING: could not open /var/tmp/mkinitramfs_kQya3Z/lib/modules/3.18.16-rpi2-6lo wpan-v7+/modules.builtin: No such file or directory /usr/sbin/update-initramfs: 204: /usr/sbin/update-initramfs: cannot create /var/ lib/initramfs-tools/3.18.16-rpi2-6lowpan-v7+: Permission denied

run-parts: /etc/kernel/postinst.d/initramfs-tools exited with return code 2 arch/arm/boot/Makefile:99: recipe for target 'install' failed make[3]: * [install]

Error 1 arch/arm/Makefile:311: recipe for target 'install' failed make[2]: [install] Error 2 make[2]: Leaving directory '/home/pi/raspbian/kernel/linux' debian/ruleset/targets/ recipe for target 'debian/stamp/install/linu x-image-3.18.16-rpi2-6lowpan-v7+' failed make[1]: [debian/stamp/install/linux-image-3.18.16-rpi2-6lowpan-v7+]

Error 2 make[1]: Leaving directory '/home/pi/raspbian/kernel/linux' debian/ruleset/ recipe for target 'kernel_image' failed make: * [kernel_image] Error 2

and I don't know how to fix the problem

ZOU gravatar image

Posted July 14, 2015, 12:13 p.m.

It seems that Bluetooth 6lowpan is now natively supported on Raspbian 2015-05-05.

pi@raspberrypi ~ $ uname -a 
Linux raspberrypi 3.18.11-v7+ #781 SMP PREEMPT Tue Apr 21 18:07:59 BST 2015 armv7l GNU/Linux

pi@raspberrypi ~ $ ls /lib/modules/3.18.11-v7+/kernel/net/bluetooth/
bluetooth_6lowpan.ko  bluetooth.ko bnep  hidp  rfcomm

Just load "bluetooth_6lowpan" in /etc/modules.

BR, zou

rols gravatar image

Posted May 19, 2016, 3:41 p.m.

I'm just working through this for a PI 3, even though the bluetooth seems to be installed already, I want to go through the process and see how it all hangs together.

Where do you select what is built into the kernel? There's no selection in the steps above that I can see, however obviously it's possible to build without things like 6lowpan, because that used to be the default.

I'm going to guess at the commands I need for the PI 3, assume I just change the chip name to the newer broadcom and continue.

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