Scripts for building root file systems for Linux development

debootstrap.sh

qemu-img create -f raw rootfs.raw 100G
mkfs.ext4 rootfs.raw
mkdir rootfs
sudo mount rootfs.raw ./rootfs   

sudo debootstrap \
    --include apt,apt-utils \
    --include isc-dhcp-client,iproute2,wget,curl \
    --include git,vim,build-essential,gcc-multilib,g++-multilib \
    focal ./rootfs http://archive.ubuntu.com/ubuntu/

sudo su
export UUID=$(blkid rootfs.raw | cut -d'"' -f 2)
echo "UUID=$UUID / ext4 errors=remount-ro 0 1" >> ./rootfs/etc/fstab
echo "vm" > ./rootfs/etc/hostname

chroot ./rootfs
echo '#!/bin/bash' > /etc/rc.local
echo "dhclient" >> /etc/rc.local 
chmod +x /etc/rc.local
useradd --create-home user
echo "root:root" | chpasswd
echo "user:user" | chpasswd
exit

umount ./rootfs

qemu-img convert -f raw -O qcow2 rootfs.raw rootfs.qcow2

initramfs.sh

curl https://busybox.net/downloads/busybox-1.36.0.tar.bz2 | tar xjf -
cd busybox-1.36.0
make defconfig
sleep 1s && sed -i 's/# CONFIG_STATIC is not set/CONFIG_STATIC=y/' ./.config
make -j$(nproc)
make install
cd _install
mkdir -pv {bin,sbin,etc,proc,sys,usr/{bin,sbin}}

cat <<'EOF' > init
#!/bin/sh
mount -t proc none /proc
mount -t sysfs none /sys
mount -t debugfs nodev /sys/kernel/debug
echo -e "\nBoot took $(cut -d' ' -f1 /proc/uptime) seconds\n"
exec /bin/sh
EOF
chmod +x init

find . -print0 \
  | cpio --null -ov --format=newc \
  | gzip -9 > ../initramfs-busybox-x86.cpio.gz