How to Install Webmin on CentOS 7
sudo nano/etc/yum.repos.d/webmin.repo

[Webmin]
name=Webmin Distribution Neutral
#baseurl=http://download.webmin.com/download/yum
mirrorlist=http://download.webmin.com/download/yum/mirrorlist
enabled=1

wget http://www.webmin.com/jcameron-key.asc
sudo rpm –import jcameron-key.asc

sudo yum install webmin

https://your_server_ip:10000/

systemctl status firewalld
systemctl disable firewalld
systemctl reload firewalld