FTP Explained
FTP is a standard network protocol used for the transfer of files between a client and server on a computer network. FTP is a very well-established protocol, developed in the 1970s to allow two computers to transfer data over the internet. One computer acts as the server to store information and the other acts as the client to send or request files from the server. The FTP protocol typically uses port 21 as its main means of communication. An FTP server will listen for client connections on port 21.

Setup proftpd

yum install epel-release -y
yum install proftpd -y
echo "/bin/false" >> /etc/shells
service proftpd start
chkconfig proftpd on

Config firewall for port 21
(centos 7)

firewall-cmd --zone=public --add-port=21/tcp --permanent
firewall-cmd --reload

(centos 6)

iptables -I INPUT -p tcp --dport 21 -j ACCEPT
service iptables save
service iptables restart

Setup user

useradd user_domain -g nginx -s /sbin/nologin -d /home/user_domain.com/public_html/
passwd user_domain

Edit user

usermod -a -G nginx user_domain -s /sbin/nologin

Add permission

chmod -R g+rw /home/user_domain.com/public_html/

Well done!