convert_debian_to_kali.sh

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

export DEBIAN_FRONTEND=noninteractive
export APT_LISTCHANGES_FRONTEND=none

log() {
  printf '[%s] %s\n' "$(date '+%F %T')" "$*"
}

die() {
  echo "Error: $*" >&2
  exit 1
}

trap 'die "Command failed on line ${LINENO}."' ERR

require_root_or_sudo() {
  if [ "$(id -u)" -ne 0 ]; then
    command -v sudo >/dev/null 2>&1 || die "sudo is required but not installed."
    sudo -v || die "sudo authentication failed."
  fi
}

check_os() {
  if [ ! -f /etc/os-release ]; then
    die "Unable to detect OS; /etc/os-release not found."
  fi

  # shellcheck disable=SC1091
  . /etc/os-release

  if [[ "${ID:-}" == "kali" ]]; then
    die "This system already reports Kali Linux."
  fi

  if [[ "${ID:-}" != "debian" && "${ID_LIKE:-}" != *debian* ]]; then
    die "This script is intended for Debian-based systems only."
  fi
}

confirm_danger() {
  cat <<'EOF'
WARNING:
This script converts a Debian system to Kali Rolling. This is risky and can break your system.
Make sure you have a full backup or a snapshot before continuing.
EOF

  read -r -p "Type 'I UNDERSTAND' to continue: " confirm
  [ "$confirm" = "I UNDERSTAND" ] || die "Aborted by user."
}

apt_update() {
  sudo apt-get update
}

apt_install() {
  sudo apt-get install -y --no-install-recommends "$@"
}

### Function to create a default user
create_default_user() {
  local password password_confirm password_hash

  if id "kali" &>/dev/null; then
    log "User 'kali' already exists. Skipping creation."
    return
  fi

  while true; do
    read -s -r -p "Provide the password for default username (kali): " password
    echo
    read -s -r -p "Confirm the password: " password_confirm
    echo
    if [[ "$password" != "$password_confirm" ]]; then
      echo "Error: Passwords do not match."
      continue
    fi
    if [[ ${#password} -lt 8 || ! "$password" =~ [A-Z] || ! "$password" =~ [a-z] || ! "$password" =~ [0-9] ]]; then
      echo "Error: Password must be at least 8 characters long and contain at least one digit, one uppercase letter, and one lowercase letter."
      continue
    fi
    break
  done

  password_hash=$(openssl passwd -6 "$password")
  sudo useradd --create-home --home "/home/kali" --password "$password_hash" --shell "/bin/bash" --groups sudo kali
  log "User 'kali' created and added to sudo group."
}

### Function to install necessary packages
install_packages() {
  local packages=(
    tzdata debconf-utils keyboard-configuration
    libncurses5-dev libncursesw5-dev wget gnupg dirmngr ca-certificates
    software-properties-common busybox xrdp lightdm
    bash-completion task-xfce-desktop
  )
  apt_update
  apt_install "${packages[@]}"
}

### Function to configure Kali Linux repositories
configure_kali_repos() {
  local sources_backup="/etc/apt/sources.list.bak.$(date '+%Y%m%d%H%M%S')"
  local keyring="/usr/share/keyrings/kali-archive-keyring.gpg"

  if [ -f /etc/apt/sources.list ]; then
    sudo cp /etc/apt/sources.list "$sources_backup"
    log "Backed up /etc/apt/sources.list to $sources_backup."
  fi

  if [ ! -f "$keyring" ]; then
    log "Installing Kali archive keyring."
    wget -q -O - https://archive.kali.org/archive-key.asc | sudo gpg --dearmor -o "$keyring"
  fi

  cat <<EOF | sudo tee /etc/apt/sources.list >/dev/null
deb [signed-by=$keyring] https://http.kali.org/kali kali-rolling main non-free contrib
deb-src [signed-by=$keyring] https://http.kali.org/kali kali-rolling main non-free contrib
EOF

  apt_update
}

### Function to install Kali Linux base packages
install_kali_packages() {
  apt_install libc6
  sudo apt-get dist-upgrade -y --fix-broken
  apt_install kali-linux-default kali-desktop-core kali-desktop-xfce spice-vdagent
}

### Function to clean up
clean_up() {
  sudo apt-get autoremove -y --purge
  sudo apt-get clean
  log "Setup completed successfully."
}

### Main script execution
require_root_or_sudo
check_os
confirm_danger
create_default_user
install_packages
configure_kali_repos
install_kali_packages
clean_up

Improving user creation by using openssl to generate a random salt and the password hash, as openssl is typically preinstalled.