Plesk: FTP error retrieving directory list

Problem:

error: Connection timed out after 20 seconds of inactivity
error: Error retrieving directory listing

Solution 1:

In SSH Terminal run the following:

echo ip_nat_ftp > /etc/modules-load.d/iptables.conf
echo ip_conntrack_ftp >> /etc/modules-load.d/iptables.conf
service xinetd restart

Source: https://unix.stackexchange.com/questions/240044/on-centos7-firewalld-overwrite-iptables-modules

Solution 2:

iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -I INPUT 2 -p tcp --match multiport --dports 49152:65535 -j ACCEPT
service iptables save
service xinetd restart

Source: https://support.plesk.com/hc/en-us/articles/213902285–How-to-configure-the-passive-ports-range-for-ProFTPd-on-a-Plesk-server-behind-a-firewall