How to install the VPN on UBUNTU systems
From a terminal, get the "openvpn" and "openvpn-auth-ldap" packages
$ sudo apt update
$ sudo apt install openvpn openvpn-auth-ldap

Verify installation using:
$ dpkg -l | grep openvpn

- Save the certificate for the vpn that, given the ira credentials, can be found at:
  https://tools.ira.inaf.it/vpn/ira-nogw.ovpn
  
  OR 
  
  - go to https://wiki.ira.inaf.it/index.php/OpenVPN_VPN
  - LOGIN IRA,
  - click on option "[1] VPN per connettersi alle reti IRA, lasciando inalterata la navigazione verso altri siti"

  The certificate can be saved into a file named, for example: ira.ovpn
 
- activate the client using:
  $ sudo openvpn --config ira.ovpn
- Enter Auth Username:
  $ your_ira_credentials (without @ira.inaf.it)
  $ your_ira_password

- ssh to the cluster as usual.

- Close VPN session using ctrl+c or "sudo pkill openvpn"