SSH is a protocol, a set of rules specifying how two computers securely communicate over a network. Secure shell is based on Sever/Client architecture, typically, a SSH Server program is installed on one computer and users on other computers run SSH client programs and are able to log in, execute commands, transfer files etc. on to the server computer.

1. To install SSH server on your Ubuntu/Debian/Mint server, run the following command:

sudo apt-get install openssh-server

2. To install SSH server on your RHEL/Centos/Fedora server, run the following command:

yum -y install openssh-server