```
#!/bin/bash

# Ensure the script is run as root
if [[ $EUID -ne 0 ]]; then
   echo "This script must be run as root. Please use sudo."
   exit 1
fi

echo "--- Updating package lists ---"
apt update

echo "--- Upgrading installed packages ---"
DEBIAN_FRONTEND=noninteractive apt upgrade -y

echo "--- Performing distribution upgrade (if available) ---"
DEBIAN_FRONTEND=noninteractive apt full-upgrade -y

echo "--- Cleaning up unnecessary packages ---"
apt autoremove -y

echo "--- Cleaning up cached package files ---"
apt clean

echo "--- Linux system update and cleanup complete! ---"

```