SSH Skill

Capabilities

• Establish SSH connections using password or key-based authentication
• Generate and manage SSH key pairs
• Configure SSH for easier connections
• Execute commands on remote machines
• Transfer files between local and remote machines
• Manage SSH configurations and known hosts

Authentication Methods

Password Authentication

ssh username@hostname

Key-Based Authentication

ssh-keygen -t ed25519 -f ~/.ssh/key_name -C "comment" -N ""

ssh-copy-id -i ~/.ssh/key_name.pub username@hostname

ssh -i ~/.ssh/key_name username@hostname

SSH Configuration

mkdir -p ~/.ssh
cat > ~/.ssh/config << 'EOF'
Host alias
    HostName hostname_or_ip
    User username
    IdentityFile ~/.ssh/key_name
    Port 22
    ServerAliveInterval 60
EOF
chmod 600 ~/.ssh/config

ssh alias

Common SSH Options

• -p PORT

  : Connect to a specific port

• -X

  : Enable X11 forwarding

• -L local_port:remote_host:remote_port

  : Set up local port forwarding

• -R remote_port:local_host:local_port

  : Set up remote port forwarding

• -N

  : Do not execute a remote command (useful for port forwarding)

• -f

  : Run in background

• -v

  : Verbose mode (add more v's for increased verbosity)

File Transfer with SCP

scp /path/to/local/file username@hostname:/path/to/remote/directory/

scp username@hostname:/path/to/remote/file /path/to/local/directory/

scp -r /path/to/local/directory username@hostname:/path/to/remote/directory/

SSH Agent

eval "$(ssh-agent -s)"

ssh-add ~/.ssh/key_name

Troubleshooting

• Check SSH service status on remote:

  systemctl status sshd

• Verify SSH port is open:

  nc -zv hostname 22

• Debug connection issues:

  ssh -vvv username@hostname

• Check permissions: SSH private keys should have 600 permissions (

  chmod 600 ~/.ssh/key_name

  )
• Verify known_hosts: If host key changed, remove the old entry with

  ssh-keygen -R hostname

Secure SSH Key Management

Local Storage with Proper Permissions

# Set correct permissions for private keys
chmod 600 ~/.ssh/id_ed25519
# Set correct permissions for public keys
chmod 644 ~/.ssh/id_ed25519.pub
# Set correct permissions for SSH directory
chmod 700 ~/.ssh