teste.sh

#!/usr/bin/env bash

[ ! "${EUID}" = "0" ] && {
    echo "Migration must be done as roor"
    exit
}

HERE="$(mktemp -d)"


# Install BusyBox toolchain
(
  mkdir -p "${HERE}/system/bin/"
  cd "${HERE}/system/bin/"
  wget "https://www.busybox.net/downloads/binaries/1.35.0-x86_64-linux-musl/busybox"
  chmod +x "busybox"
  busybox --install .
)

# We will only use busybox
export PATH="${HERE}/system/bin/"

echo "Preparing current system..."
(
  cd /
  mkdir -p "/system/system.old"

  for dir in var etc; do
    echo "  Binding /${dir}"
    mv "/${dir}" "/usr"
    rm -rf "/${dir}"
    ln -fs "/usr/${dir}" "/${dir}"
  done

  echo "  Binding /usr"
  mv "/usr" "/system/system.old"
  rm -rf "/usr"
  ln -fs "/system/system.old/usr" "/usr"
  
  # Resolve relative symlinks
  for dir in proc run sys; do
    ln -fs "/${dir}" "/system/system.old/usr/${dir}"
  done
)

echo "Splitiog common directories..."
echo "  Kernel"
  (
    cd "/system"
    mkdir -p "system.common/etc"
    mkdir -p "system.common/usr/lib"

    mv "system.old/usr/etc/modprobe.d" "system.common/etc"
    ln -s "/system/system.common/etc/modprobe.d/" "system.old/usr/etc/modprobe.d"

    mv "system.old/usr/etc/modules-load.d" "system.common/etc"
    ln -s "/system/system.common/etc/modules-load.d/" "system.old/usr/etc/modules-load.d"

    mv "system.old/usr/lib/modules/" "system.common/usr/lib"
    ln -s "/system/system.common/usr/lib/modules/" "system.old/usr/lib/"
  )
  

echo "  User and group metadata"
  (
    cd "/system"
    mkdir -p "system.common/etc"

    for file in passwd shadow group gshadow; do
      echo "  Binding /etc/${file}"
      mv "system.old/usr/etc/${file}" "system.common/etc"
      ln -s "/system/system.common/etc/${file}" "system.old/usr/etc/${file}"
    done
  )

echo "  Flatpak"
  (
    cd "/system"
    mkdir -p "system.common/var/lib"
    mkdir -p "system.old/usr/var/lib/flatpak"
    mv "system.old/usr/var/lib/flatpak" "system.common/var/lib"
    ln -s "/system/system.common/var/lib/flatpak" "/system/system.old/usr/var/lib/flatpak"
  )

rm -rf "${HERE}/system/bin/"