How to install an SFTP Server on Arduino Yùn
By default, Arduino Yùn’s Linino has Dropbear, an SSH server that procides basic SCP but has no SFTP capabilities, so you cannot connect to the Yún with client software such as Cyberduck.
You can solve this basic issue by installing OpenSSH’s SFTP Server running this command in the Arduino’s SSH console.
opkg update opkg install openssh-sftp-server
The server will be installed in /usr/libexec/sftp-server, exactly where Dropbear will look for it.