Is there any way to start GDM without start the local X server session?

Desktop
1

Hi there. As the title, I was wondering if there is any way to start GDM but without start the X server.

I’m using GNOME in a lxc container, which of course don’t have a VT by default. But I have started a X Server session on the host system, which is /tmp/.X11-unix/X1 and it’s completely for the container. I have mounted this file to the rootfs then lxc started. I now can start gnome-session using these command:

DISPLAY=:1 gnome-session

# and in archlinux, I can only open the desktop using this command

DISPLAY=:1 gnome-shell

But it’s better if I can start GDM to do the login process instead of using the console that lxc provide.

I have acknowledged that when GDM starts, it start a X server using /usr/bin/Xorg command, but even if I have changed it to a blank file, it just didn’t changed anything. I was wondering if there is a X server implement that does nothing, and I can link this to the Xorg so GDM will do nothing when start the X server and doesn’t produce any error (as I have already have the X1 socket). But I can’t find anything about that.

So I have posted a topic here to see if I can find some help here, or it just can’t be done. Thank you very much!

2

By reading the source code of gdm，I have find that with this script，you can pretend that you have running a xserver, just replace /usr/bin/X with this script.

#!/bin/sh
#
# Execute Xorg.wrap if it exists otherwise execute Xorg directly.
# This allows distros to put the suid wrapper in a separate package.

basedir="/usr/lib"

ARGS=`getopt -a -l displayfd:,auth:,nolisten:,background:,noreset,keeptty,novtswitch,verbose:,core -n 'error happened' -- "$@"`
if [ $? != 0 ]; then
    echo "Terminating..."
    exit 1
fi

#echo $ARGS
#将规范化后的命令行参数分配至位置参数（$1,$2,...)
eval set -- "${ARGS}"

fake_xorg()
{
	echo $1
	echo "0.0" >&$1
	while true
	do
		i=0
	done
}

if [ -x "$basedir"/Xorg.wrap ]; then
	echo "fake xorg"
	fake_xorg "$@"
	#exec "$basedir"/Xorg.wrap "$@"
else
	echo "fake xorg"
	fake_xorg "$@"
	#exec "$basedir"/Xorg "$@"
fi

but the new problem is Error getting tty for session id from systemd. I have checked the loginctl and the session that gdm held doesn’t have a tty. I think I’ll continue to try.

Edit: well it seems that it didn’t changed anything. sad
Edit2: it works! it turns out that it should write 0.0 instead of 0 to the fd.