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Revision as of 17:06, 10 February 2013 by MajorTom (talk | contribs) (Added a NOTE on how to allow XDMCP connections from remote hosts without XDM starting a local X server)
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This page intends to allow remote sessions using "X Display Manager Control Protocol" (XDMCP). See the GDM documention for more information on the parameters: http://library.gnome.org/admin/gdm/3.6/configuration.html.en#xdmcpsection.

Setup Graphical Logins


Modify /etc/X11/xdm/xdm-config and comment out:

DisplayManager.requestPort:    0

So it will be:

!DisplayManager.requestPort:    0

Then modify /etc/X11/xdm/Xaccess to allow any host to get a login window. Look for a line that looks like this:

*             #any host can get a login window

and remove the hash '#' sign at the beginning of the line.

In case you have multiple network interfaces also add a line like this:


Where should be you server IP address.

Then reboot or restart your X server and xdm daemon.


Modify /etc/gdm/custom.conf to include:


The restart the Gnome Display Manager:

/etc/rc.d/gdm restart

Or if using the inittab method, login as root on another tty and

telinit 3
telinit 5 && exit 


Edit kdmrc ( /opt/kde/share/config/kdm/kdmrc [KDE 3x] or /usr/share/config/kdm/kdmrc (KDE 4x] ) and at the end there should be something like this:


Then you need to restart your X server so the change you just made takes effect:

/etc/rc.d/kdm restart


SLiM doesn't support Xdmcp.

Accessing X from a remote Machine on your LAN

You can access your login manager on the network computer via the following command. TCP and UDP streams are opened. So it is not possible to access the login manager via an SSH connection.

Xnest -query -geometry 1280x1024 :1

Or, with Xephyr, if you experience refreshing problems with Xnest:

Xephyr -query -screen 1280x1024 -br -reset -terminate :1

Or, if you are on runlevel 3

X -query your_server_ip

Xserver should recognize your monitor and set appropriate resolution.

Note: You can enable XDMCP Direct/Query and Broadcast connections from remote hosts without XDM starting a local X server.

After allowing XDMCP access as described above, edit /etc/X11/xdm/Xservers and comment out:

#:0 local /usr/bin/X :0

Then launch XDM as root, e.g. xdm -config /etc/X11/xdm/archlinux/xdm-config

Thin client setup

First of all one should setup dhcp and tftp server. Dnsmasq has both of them. For network boot image check thinstation project. If your network card does not support PXE, you can try Etherboot


XDMCP fatal error: Manager unwilling Host unwilling

This is usually caused by an entry missing from the /etc/kde3/kdm/Xaccess file. This file controls which machines can connect to the server via KDM. The trick is to add a line that starts with an asterisk '*'. Look for a line that looks like:

# *                                     #any host can get a login window

and remove the hash '#' sign at the beginning of the line. Then, you need to restart KDM.

/etc/rc.d/kdm restart

Session declined: Maximum Number of Sessions Reached

Edit /etc/gdm/custom.conf and add/increase the maximum sessions.


If you still cannot log in remotely

...and you see only a black screen, try removing the -nodaemon option in /etc/inittab to have only


Login screen and GNOME is somehow flickering

If the login screen is created again and again and unresponsive, you are trying to access GNOME Shell on the remote machine. This is apparently caused by network speed, e.g. by accessing via wireless connections. The workaround is to disable/deinstall GNOME Shell.

 pacman -R gnome-shell