http://itsecforu.ru/2018/05/30/%D0%BA%D0%B0%D0%BA-%D0%BD%D0%B0%D1%81%D1%82%D1%80%D0%BE%D0%B8%D1%82%D1%8C-sftp-vsftpd-%D1%81-ssl-tls-%D0%BD%D0%B0-ubuntu-18-04/