Secure Shell (SSH)

The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution.

SSH applications are based on a client–server architecture, connecting an SSH client instance with an SSH server. SSH operates as a layered protocol suite comprising three principal hierarchical components: the transport layer provides server authentication, confidentiality, and integrity; the user authentication protocol validates the user to the server; and the connection protocol multiplexes the encrypted tunnel into multiple logical communication channels.
— Wikipedia

X11 forwarding on Android

• Start XSDL.
• Open termux and type: export DISPLAY=127.0.0.1:0
• SSH to remote host: ssh -Y user@hostname

Generate ed25519 ssh key

# -t type, -f file, -C comment
ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519 -C "Full Name <email>"

Upload an SSH Public Key

ssh-copy-id -i path_to_file.pub user@host