Is there any chance to use your client to connect my Ubuntu server to Windows machine via VPN (L2TP/IPsec)? I need to use only command line interface but not GUI. Everything is fine with connections to Windows from Android, iOS, Windows and even from Ubuntu but via GUI. All I have and all I need is: server's ip, psk key, user and password. So there is no certificates etc. Please help me.
The Ubuntu GUI will be writing config files. I suggest look at the files that it writes, then use those as a template for a simple command line tool (shell script) to turn the connection on/off.