This little script automates setting up an SSH keypair

keypair.sh

#!/bin/bash
# Handy script for doing the keypair dance

# Exit on any error
set -e

# Function to display usage
usage() {
    echo "Usage: $0 <remote_user> <remote_host>"
    echo "Example: $0 john example.com"
    exit 1
}

# Function to check if SSH key already exists
check_ssh_key() {
    if [[ -f ~/.ssh/id_rsa && -f ~/.ssh/id_rsa.pub ]]; then
        return 0
    else
        return 1
    fi
}

# Function to validate SSH connection
validate_ssh() {
    local user=$1
    local host=$2
    
    if ! ssh -o BatchMode=yes -o ConnectTimeout=5 "${user}@${host}" exit 2>/dev/null; then
        return 1
    fi
    return 0
}

# Check arguments
if [[ $# -ne 2 ]]; then
    usage
fi

REMOTE_USER="$1"
REMOTE_HOST="$2"

# Create .ssh directory if it doesn't exist
mkdir -p ~/.ssh
chmod 700 ~/.ssh

# Generate SSH key if it doesn't exist
if ! check_ssh_key; then
    echo "Generating new SSH key pair..."
    ssh-keygen -t rsa -b 4096 -f ~/.ssh/id_rsa -N ""
    if [[ $? -ne 0 ]]; then
        echo "Error: Failed to generate SSH key pair"
        exit 1
    fi
else
    echo "SSH key pair already exists, continuing..."
fi

# Check if we can already connect without password
if validate_ssh "$REMOTE_USER" "$REMOTE_HOST"; then
    echo "SSH key already set up and working!"
    exit 0
fi

# Copy SSH key
echo "Copying SSH key to remote host..."
echo "You will be prompted for the password twice:"
echo "1. First to create the .ssh directory (if it doesn't exist)"
echo "2. Then to copy the SSH key"

# Create remote .ssh directory and set permissions
ssh "$REMOTE_USER@$REMOTE_HOST" '
    mkdir -p ~/.ssh
    chmod 700 ~/.ssh
'

# Use ssh-copy-id to copy the key
ssh-copy-id -i ~/.ssh/id_rsa.pub "$REMOTE_USER@$REMOTE_HOST"
if [[ $? -ne 0 ]]; then
    echo "Error: Failed to copy SSH key"
    exit 1
fi

# Verify the setup
echo "Verifying SSH key setup..."
if validate_ssh "$REMOTE_USER" "$REMOTE_HOST"; then
    echo "Success! SSH key has been set up correctly."
    echo "You can now SSH to ${REMOTE_USER}@${REMOTE_HOST} without a password."
else
    echo "Error: SSH key setup verification failed"
    exit 1
fi