HOWTO XDMCP in Gnome

XDMCP stands for "X Display Manager Control Protocol" and is a network protocol. It allows a way of running X-Terminal on your PC (or Mac) and uses the X Server to provide a client/server interface between display hardware (the mouse, keyboard, and video displays) and the desktop environment while also providing both the windowing infrastructure and a standardized application interface. The X-Terminal can be displayed with an individual window or multiple windows, based on your X window system's software capabilities and setup.

On your X-Server, you must tweak the configuration of your graphical login manager (displaymanager).

for GDM, you need to change the [xdmcp]-section in your configfile:
/etc/X11/gdm/custom.conf

[xdmcp]
Enable=true

Depending on how your gdm.conf/custom.conf is set up, you might also need to add or change the [greeter] section as shown below. Without this, you will not be able to XDMCP in to your server.

[greeter]
Browser=true


How to use XDMCP

on the remote machine you can either use Xnest or simply X:
$ X -ac -query servername :1
or
$ Xnest -ac -query servername :1

where servername is your servername or IP. :1 is the display number. (:0 should be your running X-Server)

To change screen resolution of Xnest, use "geometry" option:
$ Xnest -geometry=1280x800 -ac -query servername :1