How to use XDMCP+GDM and Xnest?

I have been trying to enable XDMCP on GDM without much success. Following some instructions I have edited /etc/gdm/custom.conf and added:

[daemon]
RemoteGreeter=/usr/lib/gdm/gdm-xdmcp-chooser-slave
[xdmcp]
Enable=true

Then restarted gdm and tried to connect both locally and from a remote system with:

Xnest :1 -query localhost
Xnest :1 -query remote_system_hostname

I just get a black screen instead of the GDM window as expected. I am missing something ?

2 Answers

Wait for this bug to be fixed:

For LightDM which is in the latest Unity based Ubuntus I used this answer: XDMCP setup for lightdm, ports not listening

And you will probably need to also add the SeatDefaults setting in the answer i.e.

[SeatDefaults]
xserver-allow-tcp=true

And you may also need to enable access to your local server by using

xhost +<remote hostname>

or just

xhost +

to disable it completely