[Discuss] Progress report on Debian install for new system

[Alan W. Irwin]

On 2007-11-02 16:43-0700 Alan W. Irwin wrote:

> More to come concerning the following topics as I get to them:
>
> * Configuring our old shuttle as a thin client.
>

That took only a half hour (mostly spent confirming it is really so easy).
chickadee is our old computer (with a Linux distro preinstalled that
includes X).  raven is our new much faster computer (running Debian
testing).  The point of this is to give the chickadee user access to the
latest desktop software on raven transparently and at high speed.  To
implement this, the chickadee X server transmits chickadee mouse and
keyboard events to to X clients (e.g., KDE desktop applications) running on
raven, and the chickadee X server displays the results from those
applications locally on chickadee.

On raven, make sure networking on your LAN is set up so that you can ping
chickadee.  Then use

apt-get --purge remove gdm kdm ldm

to get rid of all display managers other than xdm which you install with

apt-get install xdm

(I am sure you could do something similar with any other display manager,
but xdm has been around the longest and has really clear instructions about
what to do from the man page and articles such as
http://linuxgazette.net/issue68/swieskowski.html .)

Following those xdm instructions, here is what I did:

stop xdm with

/etc/init.d/xdm stop

All the configuration files for xdm are located in
/etc/X11/xdm.  There you modify the following files:

Xservers:
I commented out

:0 local /usr/bin/X :0 vt7 -dpi 100 -nolisten tcp

if (as in my case) you prefer not to use xdm as a raven user and simply
use the startx method there instead.

Xaccess:
add

LISTEN 192.168.1.1
chickadee

to the bottom of the file to only listen on that IP address (for the
internal LAN) and only give access to chickadee on that LAN.

xdm-config:
Comment out

DisplayManager.requestPort:    0

at the bottom of file to allow XDMCP or Chooser requests to be listened for.

After those configuration changes, restart xdm with

/etc/init.d/xdm start

The chickadee configuration is even simpler.  It is assumed here that you
have X working on chickadee already and networking is set up so that "ping
raven" works over your LAN.  The all that the chickadee user has to do is
take everything down to the console mode on chickadee, then instead of
typing "startx" like they normally do to get into chickadee X, they type

X -query raven

That puts them in touch with xdm running on raven which then logs them into
that system where they have complete access as an ordinary user there
to all desktop software such as KDE.

The advantages of setting up Linux thin clients are two-fold.

(1) Very little software admin to do on chickadee any more.  The only thing
running there is the kernel + minimal GNU OS software + X. I was planning
to leave chickadee exactly as is (Debian oldstable) and forget about
even updating it any more.  After all, it is on an internal LAN with no
access to the internet so security updates are not important, and if the
kernel and X are running without problems there is no need to update them
either.  (raven does face the internet, but uses a firewall to make that
reasonably safe.)  However, see below for one last software change I want
to make for chickadee.

(2) For the chickadee user, all applications are run at raven speed, i.e.,
just as fast as if they were sitting at the raven keyboard.  Historically,
the exception to that was 3D games and 3D desktop effects where 3D graphical
data were being sent unnecessarily over the network making remote 3D apps
slow to a crawl.  For example, I found that to be a problem for the X server
for both Debian oldstable and Ubuntu dapper.  However, for the latext X
server I am running now from Debian unstable on raven, that problem has been
solved! For example, I have used ssh to login to chickadee and run
foobillard there displaying its results remotely on raven.  It ran at
effectively the same speed as the raven version for 100Mbit networking!
That's fairly subjective so I did a test with glxgears, and it ran at 2500
FPS, virtually the same rate that I get when I run it directly on raven.

So that brings me to the exception about chickadee software upgrades. Once
the latest X server stablizes a bit more (i.e, when the Debian unstable
version is debugged enough to qualify for Debian testing), I plan to install
a minimal Debian testing (just bare bones system + X server) on chickadee
and leave it alone from then on.  That new system should allow 3D raven apps
to efficiently display their results on chickadee (just like what occurs now
for the reverse situation).

To summarize this, the X-terminal idea is really easy to set up.  It allows
you to transparently speed up all your Linux computers to the effective rate
of the fastest of them and reduces the sysadmin effort considerably since
the only computer you have to update is your fastest box.  Thus, this idea
should save both cost and time for those of you with access to more than one
Linux box.

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
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Linux-powered Science
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