In this tutorial, How to checks all ports if they are closed or open and if the current ssh version? Using nmap command. Read man nmap page. The first, you have install nmap. For ubuntu $ sudo apt-get install nmap For centos $ sudo yum install nmap For example, checks for open/closed ports and current ssh version [huupv@huupv huuphan.com]$ sudo nmap -sV -p22 --version-all  localhost The output Checks for open/closed ssh ports using nmap command as below