Providing XDMCP service itself is not hard. Some configuration with XDM is enough.

But XDM has to start a X process and show something, if there is some hardware issues, it tails to start. While in my opinion, XDMCP server is pure CPU task.

So, is it possible to provide XDMCP service without using video card or screen? Just like running Nginx in background?

When I tried it in my case, the X process started by XDM died due to "no screens found". I do not want to pay attention on fixing that since local monitor means nothing to me.

I followed https://wiki.archlinux.org/index.php/XDMCP to do the modification. And xdm.log says:

xdm info (pid 1048): Starting xdm 1.1.12
xdm error (pid 1048): error binding socket address 177: Cannot assign requested address
xdm info (pid 1048): Starting X server on :0

X.Org X Server 1.20.5
X Protocol Version 11, Revision 0
Build Operating System: Linux Arch Linux
Current Operating System: Linux 9b8258ba662e 4.14.122-rancher #1 SMP Tue May 28 01:50:21 UTC 2019 x86_64
Kernel command line: BOOT_IMAGE=../vmlinuz-4.14.122-rancher printk.devkmsg=on rancher.state.dev=LABEL=RANCHER_STATE rancher.state.wait panic=10 console=tty0  initrd=../initrd-v1.5.2
Build Date: 30 May 2019  06:44:40PM

Current version of pixman: 0.38.4
    Before reporting problems, check http://wiki.x.org
    to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
    (++) from command line, (!!) notice, (II) informational,
    (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Wed Jun  5 07:05:01 2019
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
Fatal server error:
(EE) no screens found(EE) 
Please consult the The X.Org Foundation support 
     at http://wiki.x.org
 for help. 
(EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
(EE) Server terminated with error (1). Closing log file.
xdm error (pid 1048): server unexpectedly died
xdm error (pid 1048): Server for display :0 can't be started, session disabled
  • Yes it is possible (was, last time i did this). What didn't work?
    – roaima
    Jun 5 '19 at 6:33
  • 2
    @roaima, in my case, the X process started by XDM died due to "no screens found". I do not want to pay attention on fixing that since local monitor means nothing to me.
    – Magicloud
    Jun 5 '19 at 6:35
  • Should work. Could you edit to describe your X stack please, and what you changed to enable XDMCP. I'll see if I can get it working here.
    – roaima
    Jun 5 '19 at 6:54
  • 1
    @roaima, updated. And seems like lightdm does not require to start X locally. Trying that.
    – Magicloud
    Jun 5 '19 at 7:06
  • 1
    Note that session disabled should mean exactly that -- :0 will not be available, but whatever else xdm is configured to do it should still be doing.
    – rakslice
    Jun 5 '19 at 10:07

xdm starts sessions on whatever X servers are configured in /etc/X11/xdm/Xservers, with lines like

:0 local /usr/bin/X11/X vt7
otherhost:0 remote

In the case of local lines it will try to launch the X server that is specified before connecting to it.

Comment out the lines for whatever you don't want with #. If you only want XDMCP, you can comment out all of them.

  • Oh, was not aware that line. Thanks.
    – Magicloud
    Jun 5 '19 at 10:03

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