From the old (and I do mean OLD) X.Org/X Consortium bug tracker db:
Date: Mon, 30 Sep 91 20:46:00 EDT
From: Stephen Gildea <firstname.lastname@example.org>
Subject: xdmshell: missing manual page
### bug number: 4559
### area: xdm
### severity: documentation
There is no manual page for the xdmshell program.
Watch people ask questions about xdmshell on xpert.
And even in the xdm.man.cpp in the current modular tree, it says:
.SH "SEE ALSO"
.\" .IR chooser (1), \" except that there isn't a manual for it yet
.\" .IR xdmshell (1), \" except that there isn't a manual for it yet
Sorry about the phenomenal bug spam, guys. Adding xorg-team@ to the QA contact so bugs don't get lost in future.
I've never actually known what xdmshell is for, but I finally found
this in the X11R4 release notes:
Many servers set the keyboard to do non-blocking I/O under
the assumption that they are the only programs attempting to
read from the keyboard. Unfortunately, some versions of
/etc/getty (A/UX's in particular) will immediately see a
continuous stream of zero-length reads which they interpret
as end-of-file indicators. Eventually, /etc/init will dis-
able logins on that line until somebody types the following
# kill -HUP 1
Under A/UX, one alternative is to disable logins on the con-
sole and always run xdm from /etc/inittab. However, make
sure that you save a copy of the old /etc/inittab in case
something goes wrong and you have to restore logins from
over the network or from single-user mode.
Another less drastic approach is to set up an account whose
shell is the xdmshell program found in mit/clients/xdm/.
This program is not installed by default so that site
administrators will examine it to see if it meets their
needs. The xdmshell utility makes sure that it is being run
from the appropriate type of terminal, starts xdm, waits for
it to finish, and then resets the console if necessary. If
the xdm resources file (specified by the
DisplayManager*resources entry in the xdm-config file) con-
tains a binding to the abort-display action similar to the
xlogin*login.translations: #override Ctrl<Key>R: abort-display()
the console can then by restored by pressing the indicated
key (Control-R in the above example) in the xdm login win-
The xdmshell program is usually installed setuid to root but
executable only by members of a special group, of which the
account which has xdmshell as its shell is the only member:
% grep xdm /etc/passwd
x:aB9i7vhDVa82z:101:51:Account for starting up X:/tmp:/etc/xdmshell
% grep 51 /etc/group
% ls -lg /etc/xdmshell
-rws--x--- 1 root xdmgrp 20338 Nov 1 01:32 /etc/xdmshell
If the xdm resources have not been configured to have a key
bound to the abort-display() action, there will be no way
for general users to login to the console directly. Whether
or not this is desirable depends on the particular site.
Fixed in git: