Custom Linux kernel

This page introduce how you can build the Linux kernel by yourself.

Linux kernel source is provided through Github repository and updated whenever new kernel package is released. In order to build the Linux kernel, you must download its kernel source using ‘git' command and switch to the decent branch which you are willing to build.

Prerequisites

Package requirements

In order to build Linux kernel, you need to install developement packages required.

$ sudo apt install git build-essential bc flex bison libssl-dev libncurses-dev

Download the Source code

$ git clone --depth 1 https://github.com/tobetter/linux \
-b `uname -r | awk -F'.' '{print "odroid-" $1 "." $2 ".y"}'`
$ cd linux
$ git branch

Compile your custom kernel

Unline the generic desktop, your Ubuntu/Debian uses a package flash-kernel that helps to install the Linux kernel packages and the device tree file for a target device. You have to tweak a couple of things once in order to let the package flash-kernel install your custom kernel properly.

Compile

Use these commands once before preceeding.

$ cp /boot/config-$(uname -r) .config
$ sed -i "s/.*CONFIG_LOCALVERSION_AUTO.*/CONFIG_LOCALVERSION_AUTO=y/g" .config
$ echo "-odroid-arm64" > .scmversion

Then, start to compile the Linux kernel source.

$ make oldconfig
$ make -j8

Install

Use these commands once before preceeding.

$ sudo sed -i "s/^force=.*$/force=\"yes\"/g" /usr/share/flash-kernel/functions
$ sudo ln -s $PWD/arch/arm64/boot/dts /usr/lib/linux-image-$(cat include/config/kernel.release)

Then, you can install the Linux kernel image and its drivers. The boot script, the device tree file and initramfs will be updated while installing by the flash-kernel. Please note that your Linux kernel version must ends with -odroid-arm64, so ensure the last log with make modules_install.

$ sudo make modules_install
$ sudo make install

For example,

$ sudo make modules_install
...
DEPMOD  5.9.15-odroid-arm64
$ sudo make install
sh ./arch/arm64/boot/install.sh 5.9.15-odroid-arm64 \
arch/arm64/boot/Image System.map "/boot"
run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 5.9.15-odroid-arm64 /boot/vmlinuz-5.9.15-odroid-arm64
run-parts: executing /etc/kernel/postinst.d/initramfs-tools 5.9.15-odroid-arm64 /boot/vmlinuz-5.9.15-odroid-arm64
update-initramfs: Generating /boot/initrd.img-5.9.15-odroid-arm64
Using DTB: amlogic/meson64_odroidn2_plus.dtb
Installing amlogic into /boot/dtbs/5.9.15-odroid-arm64/amlogic/
Installing amlogic into /boot/dtbs/5.9.15-odroid-arm64/amlogic/
flash-kernel: installing version 5.9.15-odroid-arm64
Generating boot script u-boot image... done.
Taking backup of boot.scr.
Installing new boot.scr.
run-parts: executing /etc/kernel/postinst.d/unattended-upgrades 5.9.15-odroid-arm64 /boot/vmlinuz-5.9.15-odroid-arm64
run-parts: executing /etc/kernel/postinst.d/update-notifier 5.9.15-odroid-arm64 /boot/vmlinuz-5.9.15-odroid-arm64
run-parts: executing /etc/kernel/postinst.d/zz-flash-kernel 5.9.15-odroid-arm64 /boot/vmlinuz-5.9.15-odroid-arm64
Using DTB: amlogic/meson64_odroidn2_plus.dtb
Installing amlogic into /boot/dtbs/5.9.15-odroid-arm64/amlogic/
Installing amlogic into /boot/dtbs/5.9.15-odroid-arm64/amlogic/
flash-kernel: installing version 5.9.15-odroid-arm64
Generating boot script u-boot image... done.
Taking backup of boot.scr.
Installing new boot.scr.

Tips

Back up /boot/boot.scr

Installing your custom Linux kernel will update the boot script with the version of your custom Linux kernel. It's good idea to back up the boot script /boot/boot.scr to other file name and revert it when your custom Linux kernel boot is failed.

Multiple kernel versions

Your custom kernel won't overwrite the Linux kernel files installed with packages. So after installing your custom Linux kernel image, there would be multiple Linux kernel files in /boot directory and they can be listed with the command linux-version list.

$ linux-version list
5.9.0-odroid-arm64
5.9.15-odroid-arm64

Switching the kernel version

Suppose that you are running your custom kernel, but you want to switch to the Linux kernel version installed with a kernel which is presented as 5.9.0-odroid-arm64, you can simply switch with flash-kernel with a specific kernel version.

$ sudo flash-kernel --force 5.9.0-odroid-arm64