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SSH Command Cheatsheet

SSH Command Cheatsheet

Essential SSH commands and configuration

DevOps

SSH Command Cheatsheet

A comprehensive reference for SSH (Secure Shell) commands.

Basic Connection

Connect to Server

ssh user@hostname                    # Basic connection
ssh user@192.168.1.100              # Connect by IP
ssh -p 2222 user@hostname           # Custom port
ssh user@hostname command           # Run command and exit

SSH Keys

Generate Keys

ssh-keygen                          # Generate RSA key (default)
ssh-keygen -t ed25519               # Generate Ed25519 key (recommended)
ssh-keygen -t rsa -b 4096           # Generate 4096-bit RSA key
ssh-keygen -t ed25519 -C "email@example.com"  # With comment
ssh-keygen -f ~/.ssh/custom_key     # Custom filename

Copy Public Key

ssh-copy-id user@hostname           # Copy key to server
ssh-copy-id -i ~/.ssh/id_ed25519.pub user@hostname  # Specific key
cat ~/.ssh/id_ed25519.pub | ssh user@hostname "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"  # Manual copy

Key Management

ssh-add ~/.ssh/id_ed25519           # Add key to agent
ssh-add -l                          # List loaded keys
ssh-add -D                          # Remove all keys
ssh-add -d ~/.ssh/id_ed25519        # Remove specific key
eval "$(ssh-agent -s)"              # Start SSH agent

Port Forwarding

Local Port Forwarding

ssh -L 8080:localhost:80 user@hostname  # Forward local 8080 to remote 80
ssh -L 3306:db.example.com:3306 user@gateway  # Access DB through gateway

Remote Port Forwarding

ssh -R 8080:localhost:80 user@hostname  # Forward remote 8080 to local 80

Dynamic Port Forwarding (SOCKS Proxy)

ssh -D 1080 user@hostname           # Create SOCKS proxy on port 1080

Tunneling

SSH Tunnel

ssh -N -L 8080:localhost:80 user@hostname  # -N: no command execution
ssh -f -N -L 8080:localhost:80 user@hostname  # -f: background

Jump Host (ProxyJump)

ssh -J jumphost user@target         # Connect through jump host
ssh -J user1@jump1,user2@jump2 user@target  # Multiple jumps

File Transfer

SCP (Secure Copy)

scp file.txt user@hostname:/path/   # Copy file to remote
scp user@hostname:/path/file.txt .  # Copy file from remote
scp -r directory user@hostname:/path/  # Copy directory
scp -P 2222 file.txt user@hostname:/path/  # Custom port

SFTP

sftp user@hostname                  # Start SFTP session
# SFTP commands:
get remote_file                     # Download file
put local_file                      # Upload file
ls                                  # List remote files
lls                                 # List local files
cd /path                            # Change remote directory
lcd /path                           # Change local directory

SSH Config

~/.ssh/config

# Basic host
Host myserver
    HostName 192.168.1.100
    User john
    Port 2222

# With key
Host github
    HostName github.com
    User git
    IdentityFile ~/.ssh/github_key

# Jump host
Host target
    HostName target.example.com
    User admin
    ProxyJump jumphost

# Wildcard
Host *.example.com
    User admin
    IdentityFile ~/.ssh/company_key

Common Config Options

Host *
    ServerAliveInterval 60          # Keep connection alive
    ServerAliveCountMax 3
    Compression yes                 # Enable compression
    ForwardAgent yes                # Forward SSH agent
    StrictHostKeyChecking no        # Skip host key check (insecure!)
    UserKnownHostsFile /dev/null    # Don't save host keys

Security

Disable Password Authentication

# /etc/ssh/sshd_config
PasswordAuthentication no
PubkeyAuthentication yes
PermitRootLogin no

Change SSH Port

# /etc/ssh/sshd_config
Port 2222

Restart SSH Service

sudo systemctl restart sshd         # SystemD
sudo service ssh restart            # SysVinit

Troubleshooting

Debug Connection

ssh -v user@hostname                # Verbose
ssh -vv user@hostname               # More verbose
ssh -vvv user@hostname              # Maximum verbosity

Test Configuration

sshd -t                             # Test sshd config
ssh -G user@hostname                # Show effective config

Fix Permissions

chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_ed25519
chmod 644 ~/.ssh/id_ed25519.pub
chmod 600 ~/.ssh/authorized_keys
chmod 600 ~/.ssh/config

Advanced

X11 Forwarding

ssh -X user@hostname                # Enable X11 forwarding
ssh -Y user@hostname                # Trusted X11 forwarding

Keep Connection Alive

ssh -o ServerAliveInterval=60 user@hostname

Escape Sequences

~.                                  # Disconnect
~^Z                                 # Suspend SSH
~#                                  # List forwarded connections
~?                                  # Help

Quick Reference

Command Description
ssh user@host Connect to server
ssh-keygen Generate SSH key
ssh-copy-id user@host Copy public key
scp file user@host:/path Copy file
ssh -L 8080:localhost:80 user@host Local forward
ssh -D 1080 user@host SOCKS proxy
ssh -J jump user@target Jump host
ssh -v user@host Verbose mode

Best Practices

  1. Use Ed25519 keys instead of RSA
  2. Disable password authentication
  3. Use SSH config for convenience
  4. Change default port for security
  5. Use strong passphrases for keys
  6. Keep private keys secure (600 permissions)
  7. Use SSH agent for key management
  8. Enable two-factor authentication
  9. Monitor SSH logs regularly
  10. Keep SSH updated

Resources

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