ssh

# SSH Skill This skill provides capabilities for establishing and managing SSH connections to remote machines. Windows PowerShell equivalents for SSH config creation, key paths, ssh-agent, and permissions are in `references/windows.md`. ## 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 ```bash ssh username@hostname ``` When prompted, you should ask the user for their password or a private key. ### Key-Based Authentication Generate a new SSH key pair: ```bash ssh-keygen -t ed25519 -f ~/.ssh/key_name -C "comment" -N "" ``` Copy the public key to the remote server: ```bash ssh-copy-id -i ~/.ssh/key_name.pub username@hostname ``` Connect using the private key: ```bash ssh -i ~/.ssh/key_name username@hostname ``` ## SSH Configuration Create or edit the SSH config file for easier connections: ```bash 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 ``` Then connect using the alias: ```bash 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 Copy a file to the remote server: ```bash scp /path/to/local/file username@hostname:/path/to/remote/directory/ ``` Copy a file from the remote server: ```bash scp username@hostname:/path/to/remote/file /path/to/local/directory/ ``` Copy a directory recursively: ```bash scp -r /path/to/local/directory username@hostname:/path/to/remote/directory/ ``` ## SSH Agent Start the SSH agent: ```bash eval "$(ssh-agent -s)" ``` Add a key to the agent: ```bash 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 The most basic approach is to ensure proper file permissions: ```bash # 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 ```