This script sets up an SSH tunnel as a systemd service.

setup_ssh_tunnel.sh

#!/bin/bash

#######################################################################
# Script: setup_ssh_tunnel.sh
# Description: This script sets up an SSH tunnel as a systemd service.
# Author: Ali Haririan
# Date: November 20, 2023
# License: MIT License
#######################################################################


# Environment File Configuration
ENV_FILE_PATH="/etc/default/ssh-tunnel"

# This section creates the environment file containing configuration variables.
cat > "$ENV_FILE_PATH" <<EOL
LOCAL_PORT=<changeme; example: 22222>
TARGET_HOST=<changeme; example: 192.168.1.110>
TARGET_PORT=<changeme; example: 22>
TARGET_USERNAME=<changeme; example: joe>
TARGET_SSH_KEY_PATH=<changeme; example: /home/joe/.ssh/id_rsa>
EOL

# Systemd Service Configuration
SERVICE_FILE_PATH="/etc/systemd/system/ssh-tunnel.service"

# This section creates the systemd service file using the provided configuration.
cat > "$SERVICE_FILE_PATH" <<EOL
[Unit]
Description=SSH Tunnel Service
After=network.target

[Service]
EnvironmentFile=$ENV_FILE_PATH
ExecStart=/usr/bin/ssh -NT -o ExitOnForwardFailure=yes -o StrictHostKeyChecking=no -D \${LOCAL_PORT} -p \${TARGET_PORT} -i \${TARGET_SSH_KEY_PATH} \${TARGET_USERNAME}@\${TARGET_HOST}
RestartSec=5
Restart=always

[Install]
WantedBy=multi-user.target
EOL

# Reload systemd to apply changes
sudo systemctl daemon-reload

# Enable and start the SSH tunnel service
sudo systemctl enable ssh-tunnel.service
sudo systemctl start ssh-tunnel.service

# Completion Message
echo "SSH tunnel service configured and started successfully."