Saturday, November 17, 2018

LightDM not responding to XDMCP requests 12.04 LTS

Since a recent upgrade from 10.04 LTS to 12.04 LTS I can no longer login using XDMCP (ssh -XC is okay).


This is similar to an earlier question but the answer (add xserver-allow-tcp=true) didn't help me.


I have followed the instruction to setup LightDM as an XDMCP server as follows:


/etc/lightdm/lightdm.conf


[SeatDefaults]
user-session=ubuntu
greeter-session=unity-greeter
xserver-allow-tcp=true
[XDMCPServer]
enabled=true

And then restarted by


sudo restart lightdm


I have the following in /var/log/lightdm.log


[+0.01s] DEBUG: Waiting for ready signal from X server :0
[+0.01s] DEBUG: Starting XDMCP server on UDP/IP port 177
[+0.01s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
[+0.01s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0
[+0.18s] DEBUG: Got signal 10 from process 4925
[+0.18s] DEBUG: Got signal from X server :0
[+0.18s] DEBUG: Connecting to XServer :0

netstat -l | grep xdmcp gives


udp        0      0 *:xdmcp                 *:*
udp6 0 0 [::]:xdmcp [::]:*

which seems okay (although others had said there should be a TCP port 6000 here as well).


The firewall port is open:


sudo ufw status


177                        ALLOW       Anywhere
6000 ALLOW Anywhere
22 ALLOW Anywhere (v6)
177 ALLOW Anywhere (v6)

But no go:


Xephyr :2 -query *


[dix] Could not init font path element /usr/share/fonts/X11/cyrillic, removing from list!
[dix] Could not init font path element /usr/share/fonts/X11/100dpi/:unscaled, removing from list!
[dix] Could not init font path element /usr/share/fonts/X11/75dpi/:unscaled, removing from list!
[dix] Could not init font path element /usr/share/fonts/X11/100dpi, removing from list!
[dix] Could not init font path element /usr/share/fonts/X11/75dpi, removing from list!
XDM: too many retransmissions, declaring session dead

Does anyone have any clues, or even how I can go about debugging this?


Many thanks!!

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