The Linux Kernel

At first, compile the Linux kernel, https://kernel.org/ and grab the latest Linux kernel.

wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.7.1.tar.xz
tar xf linux-6.7.1.tar.xz
cd linux-6.7.1.tar.xz

General preparation environment to compile the kernel...

sudo apt install build-essential libncurses-dev bison flex libssl-dev libelf-dev

To configure the kernel:

make defconfig

This will create the default config file for compiling Linux. Then run

make menuconfig

to enter a TUI to edit the config file. One thing for older devices is unchecking 64 bit kernel. Use make -j $(nproc) to compile using all the CPU cores.

# Example: Using 4 parallel jobs
make -j4

After compiling, you should get the arch/x86/boot/bzImage . If not, check the make file log.

BusyBox

Next use BusyBox to create a minimal file system. Get the source code and extract it.

wget https://busybox.net/downloads/busybox-1.36.1.tar.bz2
tar xf busybox-1.36.1.tar.bz2
cd busybox-1.36.1

Run...

make defconfig

to make a default configuration for the BusyBox. Then...

make menuconfig

to bring the TUI and edit the configs. The option which you must edit is located in Settings, and then Build static binary (no shared libs). The reason to enable this option is we do not want to compile Glibc into the Linux distro.

Use..

make -j $(nproc)

to compile BusyBox. To check if the compiled file is fine, use command...

file busybox

The file must be statically linked.