(Here follows an almost verbatim copy of a self-answer from an identical question on serverfault which I'd forgotten about; askubuntu wasn't yet created).
Based on information found in this page about enabling XDCMP and the file /etc/gdm/gdm.schemas, I managed to create a /etc/gdm/custom.conf
file:
# /etc/gdm/custom.conf
[xdmcp]
[chooser]
[security]
DisallowTCP=false
[debug]
Take care with letter case: it won't work, if you write "disallowTCP=false"...
I also changed the /etc/X11/xinit/xserverrc file to:
exec /usr/bin/X11/X
i.e. I removed the -nolisten tcp
options to the X executable. I don't know if I needed to. You might want to try avoiding this edit.
If you only change the xserverrc file, X will nevertheless start with "-nolisten TCP".
After that, all that is needed is a restart of the gdm process:
sudo service gdm restart
You can verify the success as:
tzot@tzot-laptop:/etc/X11
$ netstat -an | grep -F 6000
tcp 0 0 0.0.0.0:6000 0.0.0.0:* LISTEN
tcp6 0 0 :::6000 :::* LISTEN
Update
After an upgrade to 12.04, I had the same issue. This time, the culprit is the lightdm that the system uses. The file that needs to be updated is /etc/lightdm/lightdm.conf
and the required addition is a xserver-allow-tcp=true
in the [SeatDefaults]
section.
And afterwards, I also found that answer. :)
Synopsis
So, in 10.10 this still works: create /etc/gdm/custom.conf
with contents as specified above and restart gdm
.