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" (EE) Fatal server error: (EE) no screens found(EE) (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) (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