Minimal Linux script

minimal-linux.sh

#!/bin/bash

# For this script you'll need gcc, gzip make, qemu, tar, wget
# Learn more on my blog: https://labs.davlgd.fr/posts/2024-05-whats-a-minimal-linux/

# Get and compile the kernel
wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.8.8.tar.xz
tar xf linux-6.8.8.tar.xz
cd linux-6.8.8/

make defconfig
make -j$(nproc)

# Get, decompress and compile BusyBox
wget https://busybox.net/downloads/busybox-1.36.1.tar.bz2
tar xf busybox-1.36.1.tar.bz2
cd busybox-1.36.1/

# Configure and set CONFIG_STATIC=y to get a standalone binary
make defconfig
sed -i 's/# CONFIG_STATIC is not set/CONFIG_STATIC=y/' .config
make -j$(nproc)

# Create initramfs folder, install BusyBox in it
mkdir ../initramfs
make install CONFIG_PREFIX=../initramfs

# Create needed folders and init script
cd ../initramfs/
mkdir {dev,proc,sys}
cat > init <<EOF
#!/bin/sh

mount -t devtmpfs none /dev
mount -t proc none /proc
mount -t sysfs none /sys

echo "Welcome to my minimal Linux system!"
uname -a

# Understand this command: https://busybox.net/FAQ.html#job_control
exec setsid cttyhack /bin/sh
EOF
chmod +x init

# Create initramfs compressed archive
find . | cpio -H newc -o | gzip > ../initramfs.cpio.gz
cd ..

# Launch the emulated system with minimal Linux
qemu-system-x86_64 --enable-kvm -cpu host -kernel arch/x86/boot/bzImage -initrd initramfs.cpio.gz -append "console=ttyS0 panic=1" -nographic -no-reboot