Questions[xserver](ubuntu)

I have a legacy program (since 1992) on a dedicated remote machine as an X-client that while starting up tries to fix all kinds of oddities using xmodmap and the like. Starting with 18.04 I note that many of these fixes no longer work.

How can (or should) the X-client detect that unity is running on the X-server? Or, to put it differently: What information does unity offer to X-clients beyond xdpyinfo and the like?

The connecting X-servers are more than 50 of various configurations (XQuartz, Ubuntu, Cygwin, and many Linuxes I never heard of before). They connect indirectly to the X-client otherwise known as a server.

This was asked before, but it wasn't answered, so I'm not sure what to do here, After switching to Intel to save battery power in the Nvidia X server settings I couldn't open it any more when I click it just does nothing.

My OS is Ubuntu 18.04 LTS

Or maybe it was because I installed Nvidia driver 396. If so, I don't know how to uninstall it, purging Nvidia didn't remove it at all.

$ inxi-MG
Machine:   Device: laptop System: Dell product: Inspiron 7559 v: 1.2.8 serial: N/A
           Mobo: Dell model: 0H0CC0 v: A00 serial: N/A
           UEFI: Dell v: 1.2.8 date: 05/14/2018
Graphics:  Card-1: Intel HD Graphics 530
           Card-2: NVIDIA GM107M [GeForce GTX 960M]
           Display Server: x11 (X.Org 1.19.6 ) driver: nvidia
           Resolution: [email protected]
           OpenGL: renderer: Mesa DRI Intel HD Graphics 530 (Skylake GT2)
           version: 4.5 Mesa 18.0.5

What is this script doing?

#!/bin/bash
xhost +local:
xhost +si:localuser:root

What is the default list of xhost?

I remember reading that servers do not have a GUI because X11 is a security risk. Why?

I have been using Ubuntu for quite some time but, I have no idea what the X server is? I hear it quite often.

I would like to know what the X Server is and what it does. How ~/.xinitrc file is used and knowing what the x.org does in the realm of X Server?