There are two main methods for building the kernel. You can build locally on a Raspberry Pi, which will take a long time; or you can cross-compile, which is much quicker, but requires more setup.
On a Raspberry Pi, first install the latest version of Raspbian. Then boot your Pi, plug in Ethernet to give you access to the sources, and log in.
First get the sources, which will take some time:
git clone --depth=1 https://github.com/raspberrypi/linux
Add missing dependencies:
sudo apt-get install bc
Run the following commands, depending on your Raspberry Pi version.
Raspberry Pi 1 (or Compute Module) default build configuration
cd linux KERNEL=kernel make bcmrpi_defconfig
Raspberry Pi 2/3 default build configuration
cd linux KERNEL=kernel7 make bcm2709_defconfig
Build and install the kernel, modules, and Device Tree blobs; this step takes a long time:
make -j4 zImage modules dtbs sudo make modules_install sudo cp arch/arm/boot/dts/*.dtb /boot/ sudo cp arch/arm/boot/dts/overlays/*.dtb* /boot/overlays/ sudo cp arch/arm/boot/dts/overlays/README /boot/overlays/ sudo scripts/mkknlimg arch/arm/boot/zImage /boot/$KERNEL.img
Note: On a Raspberry Pi 2/3, the
-j4 flag splits the work between all four cores, speeding up compilation significantly.
First, you will need a suitable Linux cross-compilation host. We tend to use Ubuntu; since Raspbian is also a Debian distribution, it means many aspects are similar, such as the command lines.
You can either do this using VirtualBox (or VMWare) on Windows, or install it directly onto your computer. For reference, you can follow instructions online at Wikihow.
Use the following command to install the toolchain:
git clone https://github.com/raspberrypi/tools
You can then copy the
/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian directory to a common location, and add
/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/bin to your $PATH in the
.bashrc in your home directory. For 64-bit host systems, use
/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin. While this step isn't strictly necessary, it does make it easier for later command lines!
To get the sources, refer to the original GitHub repository for the various branches.
$ git clone --depth=1 https://github.com/raspberrypi/linux
To build the sources for cross-compilation, there may be extra dependencies beyond those you've installed by default with Ubuntu. If you find you need other things, please submit a pull request to change the documentation.
Enter the following commands to build the sources and Device Tree files:
For Pi 1 or Compute Module:
cd linux KERNEL=kernel make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bcmrpi_defconfig
For Pi 2/3:
cd linux KERNEL=kernel7 make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bcm2709_defconfig
Then, for both:
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs
Note: To speed up compilation on multiprocessor systems, and get some improvement on single processor ones, use
-j n, where n is the number of processors * 1.5. Alternatively, feel free to experiment and see what works!
Install directly onto the SD card
Having built the kernel, you need to copy it onto your Raspberry Pi and install the modules; this is best done directly using an SD card reader.
lsblk before and after plugging in your SD card to identify it. You should end up with something like this:
sdb sdb1 sdb2
sdb1 being the FAT (boot) partition, and
sdb2 being the ext4 filesystem (root) partition.
If it's a NOOBS card, you should see something like this:
sdb sdb1 sdb2 sdb5 sdb6 sdb7
sdb6 being the FAT (boot) partition, and
sdb7 being the ext4 filesystem (root) partition.
Mount these first, adjusting the partition numbers for NOOBS cards:
mkdir mnt/fat32 mkdir mnt/ext4 sudo mount /dev/sdb1 mnt/fat32 sudo mount /dev/sdb2 mnt/ext4
Next, install the modules:
sudo make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- INSTALL_MOD_PATH=mnt/ext4 modules_install
Finally, copy the kernel and Device Tree blobs onto the SD card, making sure to back up your old kernel:
sudo cp mnt/fat32/$KERNEL.img mnt/fat32/$KERNEL-backup.img sudo scripts/mkknlimg arch/arm/boot/zImage mnt/fat32/$KERNEL.img sudo cp arch/arm/boot/dts/*.dtb mnt/fat32/ sudo cp arch/arm/boot/dts/overlays/*.dtb* mnt/fat32/overlays/ sudo cp arch/arm/boot/dts/overlays/README mnt/fat32/overlays/ sudo umount mnt/fat32 sudo umount mnt/ext4
Another option is to copy the kernel into the same place, but with a different filename - for instance, kernel-myconfig.img - rather than overwriting the kernel.img file. You can then edit the config.txt file to select the kernel that the Pi will boot into:
This has the advantage of keeping your kernel separate from the kernel image managed by the system and any automatic update tools, and allowing you to easily revert to a stock kernel in the event that your kernel cannot boot.
Finally, plug the card into the Pi and boot it!