Install an OpenVPN client for Linux, open Terminal and type in sudo apt-get install openvpn (This command sudo apt-get install openvpn is for Ubuntu/Debian. If you have Fedora/CentOS/RedHat, then use this command, sudo yum install openvpn). Type in your password to begin installation. Test that OpenVPN has been installed, type in openvpn --version.
Login to Members area, and create and download a certificate for OpenVPN with configuration files. Click on Members, login to your account, then click VPN Services, and then click on OpenVPN certificates generation.
Under Add new certificate, for Description type in Linux-CLI-OpenVPN, and then click on Add to my certificates button. Once your certificate has been created, click on Download button to download the OpenVPN configuration files.
By default files are downloaded to /tmp/ folder on your linux. In our case exact file location of zipped OpenVPN certificates is /tmp/Astrill-Linux-CLI-OpenVPN.zip. I have created a new folder on Desktop, called Astrill-OpenVPN, exact location is /root/jovica/Desktop/Astrill-OpenVPN, I change current location to that directory. To unzip OpenVPN certificates, type in unzip /tmp/Astrill-Linux-CLI-OpenVPN.zip
Run the OpenVPN client with the downloaded client config file. You can use any VP server, type in sudo openvpn --config 01-USA-Dallas-1.ovpn. If you see Initialization Sequence Completed, that means you are successfully connected to Astrill OpenVPN.