Gets ZeroTier IP and sets it as the only host able to access SSH

zerotier_auto_ssh_config.sh

#!/bin/bash

# Make sure you've already setup ZeroTier or this will kick you out

ZTIP=$(ip -4 -o addr show | awk '$2 ~ /^zt*/ {print $2, $4}' | cut -f2 -d' ' | cut -f1 -d'/')

# Check if ZTIP has a value
if [[ -z "$ZTIP" ]]; then
  echo "Error: ZeroTier IP address not found. Make sure ZeroTier is installed and running."
  exit 1
fi

# Backup the files
sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak
sudo cp /lib/systemd/system/ssh.socket /lib/systemd/system/ssh.socket.bak

# sshd_config set IP
sudo sed -i "s/^ListenAddress.*/ListenAddress $ZTIP/" /etc/ssh/sshd_config

# /lib/systemd/system/ssh.socket set IP
sudo sed -i "s=^ListenStream.*=ListenStream=$ZTIP:22=" /lib/systemd/system/ssh.socket

sudo dpkg-divert --no-rename --divert /lib/systemd/system/ssh.socket.diverted /lib/systemd/system/ssh.socket
sudo systemctl daemon-reload
sudo systemctl restart ssh.socket
sudo systemctl restart ssh

# Prompt for authentication method
read -p "Do you use SSH keys for authentication? (yes/no) " use_keys

if [[ "$use_keys" == "yes" ]]; then
  # Check destination reachability using key-based authentication
  if ! ssh -o "BatchMode=yes" -o "ConnectTimeout=5" "$ZTIP" "echo 'OK'"; then
    echo "Error: Destination unreachable using key-based authentication. Restoring backups..."
    restore_backups
    exit 1
  else
    echo "Destination reachable. SSH configuration updated successfully!"
  fi
elif [[ "$use_keys" == "no" ]]; then
  # Prompt for password
  read -sp "Enter password for $ZTIP: " password
  echo

  # Check destination reachability using password authentication
  if ! sshpass -p "$password" ssh -o "BatchMode=yes" -o "ConnectTimeout=5" "$ZTIP" "echo 'OK'"; then
    echo "Error: Destination unreachable using password authentication. Restoring backups..."
    restore_backups
    exit 1
  else
    echo "Destination reachable. SSH configuration updated successfully!"
  fi
else
  echo "Invalid input. Please enter 'yes' or 'no'."
  restore_backups
  exit 1
fi

# Function to restore backups
restore_backups() {
  sudo cp /etc/ssh/sshd_config.bak /etc/ssh/sshd_config
  sudo cp /lib/systemd/system/ssh.socket.bak /lib/systemd/system/ssh.socket

  sudo dpkg-divert --no-rename --divert /lib/systemd/system/ssh.socket.diverted /lib/systemd/system/ssh.socket
  sudo systemctl daemon-reload
  sudo systemctl restart ssh.socket
  sudo systemctl restart ssh
}