Abaixo procedimento para ativar o sftp no servidor ftp ProFTPD
cd /usr/local/directadmin/custombuild
./build set ftpd proftpd
mkdir -p custom/proftpd
wget -O custom/proftpd/configure.proftpd http://files.directadmin.com/services/all/sftp/configure.proftpd.sftp
chmod 755 custom/proftpd/configure.proftpd
./build proftpd
chmod 600 /etc/ssh/ssh_host_rsa_key
ssh-keygen -f /etc/ssh/ssh_host_dsa_key -N '' -t dsa
service proftpd restart