/etc/X11/xdm/Xservers uses old /usr/bin/X not Xorg

[Roman Fiedler]

Binary package hint: xdm

After a minimal install of xserver and xdm, xdm does not start because X binary cannot be started. It is possible, that this is not a bug of xdm itself, please see note of workaround below:

Cause:

File /etc/X11/xdm/Xservers refers to X via /usr/bin/X

:0 local /usr/bin/X :0 vt7 -nolisten tcp

No such file or symbolic link exists, but /usr/bin/Xorg exists.

# WORKAROUND: Might be bug in ubuntu xdm or xserver package,
# reported launchpad #?NOTYET. Not clear, if xdm base config is
# broken, xorg install failed to create symlink or our install instructions
# broke it.
if ! test -e /usr/bin/X; then
  sed -i -r -e 's/ \/usr\/bin\/X / \/usr\/bin\/Xorg /' /etc/X11/xdm/Xservers
fi

[Timo Aaltonen (tjaalton)]

you just need to install xserver-xorg too.

[Roman Fiedler (roman-fiedler-deactivatedaccount)]

So the lightweighted xserver-xorg-core package, which is sufficient to work with fvwm and other window manager is not sufficient for xdm, which just displays a banner? A full xserver installation is needed instead? What is the difference between the

/usr/bin/X binary and the /usr/bin/Xorg binary? It seems that the second can fully replace the first one, at least for xdm. Is there a security problem using Xorg directly?