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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: https://help.gnome.org/admin/gdm/3.26/gdm.html#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 the xdm daemon.


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


Then restart gdm.service.

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

telinit 3
telinit 5 && exit


Support for this feature seems to be very buggy. Lightdm is probably an easier choice.

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 kdm.service so the change you just made takes effect.


Modify /etc/lightdm/lightdm.conf

Enable the XDMCP Server:


On a headless system, disable the automatic start of one seat so that LightDM can run in the background:


Then restart lightdm.service.

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 server address

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

Example GUI-based Clients


Session declined: Maximum Number of Sessions Reached

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