To install X2Go server on Debian, add the key
apt-key adv --recv-keys --keyserver keys.gnupg.net E1F958385BFE2B6E
Now add X2Go repo by editing file
vi /etc/apt/sources.list.d/x2go.list
For debian 9, add
deb http://packages.x2go.org/debian stretch main
If you are using different debian version, replace stretch with name of your debian version. You can find this with command lsb_release -a
root@hon-vpn:~# lsb_release -a No LSB modules are available. Distributor ID: Debian Description: Debian GNU/Linux 9.2 (stretch) Release: 9.2 Codename: stretch root@hon-vpn:~#
Now install with
apt update apt -y install x2goserver x2goserver-xsession