Linux Passwordless oneliner
TARGET=user@host; PORT=22; [[ -r ~/.ssh/id_ed25519.pub ]] || ssh-keygen -t ed25519 -N "" -f ~/.ssh/id_ed25519; ssh -p "$PORT" "$TARGET" 'umask 077; mkdir -p ~/.ssh && cat > ~/.ssh/authorized_keys' < ~/.ssh/id_ed25519.pub && ssh -p "$PORT" "$TARGET" 'echo ">>> Root доступ подтверждён"'