SSH & PuTTY Cheatsheet

Quick Summary

SSH (Secure Shell) is a cryptographic network protocol for secure remote access and file transfer. PuTTY is a popular SSH client for Windows. Essential for remote server management, secure file transfers, and tunneling.

Importance

  • Remote Access: Secure connection to servers and devices
  • File Transfer: Secure copying of files between systems
  • Tunneling: Create secure tunnels for network traffic
  • Automation: Script remote commands and deployments
  • Security: Encrypted communication over unsecured networks

Basic Setup & Installation

SSH Client Installation 

# Ubuntu/Debian
sudo apt update
sudo apt install openssh-client

# CentOS/RHEL
sudo yum install openssh-clients

# macOS (usually pre-installed)
ssh --version

PuTTY Installation (Windows)

  1. Download from: https://www.putty.org/
  2. Install or use portable version
  3. Configure saved sessions for easy access

Essential Commands

SSH Connection 

# Basic connection
ssh username@hostname

# Connect with specific port
ssh -p 2222 username@hostname

# Connect with key file
ssh -i /path/to/private_key username@hostname

# Connect with verbose output
ssh -v username@hostname

# Connect and execute command
ssh username@hostname "command"

SSH Key Management 

# Generate SSH key pair
ssh-keygen -t rsa -b 4096 -C "your_email@example.com"

# Copy public key to server
ssh-copy-id username@hostname

# Add key to SSH agent
ssh-add /path/to/private_key

# List loaded keys
ssh-add -l

SCP (Secure Copy) 

# Copy file to remote server
scp file.txt username@hostname:/remote/path/

# Copy file from remote server
scp username@hostname:/remote/path/file.txt ./

# Copy directory recursively
scp -r local_directory/ username@hostname:/remote/path/

# Copy with specific port
scp -P 2222 file.txt username@hostname:/remote/path/

SFTP (SSH File Transfer Protocol) 

# Connect to SFTP
sftp username@hostname

# SFTP commands
get remote_file local_file    # Download file
put local_file remote_file   # Upload file
ls                           # List remote directory
lls                          # List local directory
cd remote_directory          # Change remote directory
lcd local_directory          # Change local directory

SSH Tunneling 

# Local port forwarding
ssh -L 8080:localhost:80 username@hostname

# Remote port forwarding
ssh -R 8080:localhost:80 username@hostname

# Dynamic port forwarding (SOCKS proxy)
ssh -D 1080 username@hostname

PuTTY Configuration

Basic Settings

  • Host Name: IP address or hostname
  • Port: 22 (default SSH port)
  • Connection Type: SSH
  • Saved Sessions: Name and save for reuse

Advanced Settings

  • Connection > SSH > Auth: Private key file path
  • Connection > Data: Auto-login username
  • Terminal: Terminal type and features
  • Window: Window size and behavior

PuTTY Key Generation

  1. Run PuTTYgen
  2. Generate new key pair (RSA 2048+)
  3. Save private key (.ppk format)
  4. Copy public key to server

Security Best Practices

Key Management 

# Use strong passphrases for keys
ssh-keygen -t ed25519 -C "your_email@example.com"

# Disable password authentication (use keys only)
# Edit /etc/ssh/sshd_config
PasswordAuthentication no
PubkeyAuthentication yes

SSH Configuration 

# Client configuration (~/.ssh/config)
Host myserver
    HostName 192.168.1.100
    User myusername
    Port 22
    IdentityFile ~/.ssh/id_rsa
    ServerAliveInterval 60

Server Hardening 

# Edit /etc/ssh/sshd_config
PermitRootLogin no
MaxAuthTries 3
ClientAliveInterval 300
ClientAliveCountMax 2

Troubleshooting

Common Issues 

# Permission denied (publickey)
ssh-add -l  # Check loaded keys
ssh-add ~/.ssh/id_rsa  # Add key to agent

# Connection refused
telnet hostname 22  # Test if port is open
ssh -v username@hostname  # Verbose connection

# Host key verification failed
ssh-keygen -R hostname  # Remove old host key

Debugging 

# Verbose SSH connection
ssh -vvv username@hostname

# Test SSH connection
ssh -T git@github.com  # Test GitHub SSH

# Check SSH agent
ssh-add -l
echo $SSH_AUTH_SOCK

Useful Aliases 

# Add to ~/.bashrc or ~/.zshrc
alias sshserver='ssh -i ~/.ssh/server_key user@server.com'
alias sshdev='ssh -L 3000:localhost:3000 dev@dev-server.com'
alias sshprod='ssh -L 8080:localhost:80 prod@prod-server.com'

References