Xwall version 2.0

INTRODUCTION

Are you tired of seeing wall messages splatting across every xterm
on an X display?  We decided to change the way the wall worked in
the presence of X.

We made an xwalld daemon that would attach to the X display and listen
for messages from the xwall program.  The xwalld daemon is hardy enough
to survive server resets and X terminals disappearing for a while.  The
xwall program passes the message to the xwalld using selections.  The
message passing is done in accordance with the ICCCM.

Later, we added the ability to capture console messages to walld.

SECURITY

We have patched R4 xdm to issue the server key to root.  We feel that this
is not a security problem.  Root can always assume the identity of the
user to gain access to the X display.  Apply xdm.patch to enact this
change.  We run most displays with authorization turned on and server
grabbing turned off.  This allows wall messages to appear when nobody
is logged in.

Both xwalld and xwall are setuid root programs.  We have carefully examined
both programs for security loop holes.  Xwalld needs to run as root to be
able to connect to the X display when nobody is logged in.  Xwall needs to
run as root to be able to switch the uid when a user is using a remote
X display.

CHANGES FOR X11R5

The xwalld daemon no longer respawn itself when the X server connection
is lost.  This was required for R4, because there was no way to have xdm
start xwalld when nobody was logged in.  This functionality is provided
in R5 with the Xsetup script.  Xwalld will automatically be configured to
respawn for R4 and not respawn for R5.

Since the xconsole client is provided with R5, the console support has
been withdrawn from xwalld.

INSTALLATION

For X11R4:

In addition to installing the programs, you should install xdm.patch.
I have also included our modified copy of the 4.3 BSD /bin/wall program.
It checks the utmp entries for X connections.  It attempts to use xwall
and falls back to the old method if xwall fails.  Be sure to adjust the
path used to call xwall to match your local installation.

If you want xwall messages to appear when nobody is logged in,
use something like the following in your xdm-config.

DisplayManager._0.authorize:    true
DisplayManager._0.authFile:     /usr/adm/xdm/auth-server
DisplayManager._0.grabServer:   false

For X11R5:

In addition to installing the programs.  Look at the example Xsetup
files and change your xdm Xsetup file to issue the keys to root and
start xwalld.  Also modify your Xreset file to revoke the keys.


TESTED PLATFORMS

Xwall and xwalld have been installed and tested on the following platforms:

DecStation 3100, Ultrix 3.1 & 4.0 & 4.2 (Using X11R4/R5, not DecWindows)
VaxStation 3200, Ultrix 3.1       (Using X11R4, not DecWindows)
Sun 4/100,       SunOS 4.1
Sun 3/50,        SunOS 4.1
IBM RT,          AOS 4.3
Hp bobcat,       BSD 4.3
Convex C220      ConvexOS 9.0     (X11R4)
Cray Y-MP8/864   UNICOS 5.1.11    (Using X11r4, not r3 as supplied by CRI)

Xwall and xwalld have also been tested with NCD-16 X terminals.

FEEDBACK

I welcome any feedback that you care to give.  Of course, I am interested
in your success stories.  I will also try to help you if you have problems.
However, I cannot make any promise of support.

Tim Theisen             Department of Computer Sciences
tim@cs.wisc.edu         University of Wisconsin-Madison
uwvax!tim               1210 West Dayton Street
(608)262-0438           Madison, WI   53706