BASH

Create a Secure SSH Tunnel for Local Port Forwarding

Establish a secure SSH tunnel to forward a remote port to a local port, enabling access to services on a remote network as if they were local.

#!/bin/bash

# Configuration
REMOTE_HOST="your_remote_server.com" # The remote server's hostname or IP
REMOTE_USER="ssh_user"             # Your SSH username on the remote server
REMOTE_SERVICE_IP="127.0.0.1"      # IP of the service on the remote server (often localhost relative to the SSH server)
REMOTE_SERVICE_PORT="3306"         # The port of the service on the remote server (e.g., MySQL)
LOCAL_LISTEN_PORT="3307"           # The local port you want to use to access the service

# Optional: Path to your SSH private key
# SSH_KEY="~/.ssh/id_rsa"

# Check if SSH is installed
if ! command -v ssh &> /dev/null
then
    echo "SSH client could not be found. Please install OpenSSH client."
    exit 1
fi

echo "Attempting to establish SSH tunnel..."
echo "Local access: localhost:$LOCAL_LISTEN_PORT -> $REMOTE_HOST:$REMOTE_SERVICE_PORT"

# Construct SSH command for local port forwarding (-L)
# -N: Do not execute a remote command.
# -T: Disable pseudo-terminal allocation.
# -L: Local port forwarding: [local_port]:[remote_host]:[remote_port]
# -f: Go to background after authentication (optional, useful for daemonizing)
# -q: Quiet mode
# -i: Specify identity file (private key)

SSH_COMMAND="ssh -N -L $LOCAL_LISTEN_PORT:$REMOTE_SERVICE_IP:$REMOTE_SERVICE_PORT $REMOTE_USER@$REMOTE_HOST"

# if [ -n "$SSH_KEY" ]; then
#     SSH_COMMAND="$SSH_COMMAND -i '$SSH_KEY'"
# fi

# Run in background with `&` or foreground without it
$SSH_COMMAND &

if [ $? -eq 0 ]; then
    echo "SSH tunnel established. You can now connect to localhost:$LOCAL_LISTEN_PORT."
    echo "To terminate the tunnel, find the process ID (ps -ef | grep ssh) and kill it."
else
    echo "Failed to establish SSH tunnel. Check your SSH configuration and credentials."
    exit 1
fi

How it works: This script creates a secure SSH tunnel using local port forwarding. It maps a port on your local machine (`LOCAL_LISTEN_PORT`) to a specific port on a remote server (`REMOTE_SERVICE_PORT`). This allows you to securely access services running on the remote server (e.g., a database like MySQL or PostgreSQL, or a web service not directly exposed) as if they were running locally. The `-N` flag prevents executing remote commands, and `-L` defines the port forwarding. Running it in the background (`&`) is convenient for continuous access during development.

Create a Secure SSH Tunnel for Local Port Forwarding

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