[VHFcontesting] Multihead Xwindows

[John D'Ausilio]

There's probably a relatively small audience for this .. but here's
the info anyway ;)

The power budget in the Integalactic Roving Battle Jitney has been
under some stress since the last rebuild. The obvious place to cut
some power was in the computer category .. we've been running a pair
of IBM Netfinity p4 boxes, one for each op, plus a laptop for gps/nav
up front. I started looking into ways to eliminate one of the boxes
(and maybe a couple hundred watts of consumption).

The Jitney is linux-based, we run roverlog integrated with rotors,
keyers and radios. I started reading up on multiseat Xwindows systems
.. essentially running two seperate X sessions on one box, each of
which has it's own monitor/keyboard/mouse. I accquired a
small-form-factor dual head Nvidia graphics cards and a couple of
serial port cards and installed them in one of the p4 boxes. No
problem getting dual-head working, either twinview/xinerama or as
seperate X servers.

Multihead systems are set up either as two entirely seperate X servers
(essential if you want to use glx for gaming and such) or using the
Xephyr nested Xserver system (no glx but works with dual-head video
cards that don't expose two seperate pci addresses). A guy down in
Brazil had done a bunch of work making this relatively easy .. but not
for my nvidia card (which is one of those with only one pci address).
I spent a week hacking around trying to make it work, and finally was
about to give up when I ran across userful.com.  Userful is a
commercial multiseat system for linux, but they offer free
non-commercial 2-seat licenses to anyone who asks. And even better,
it's in ubuntu's repositories so all I had to do was install
"desktop-extender" and reboot and magically everything works! When it
comes up it flashes the lights on each keyboard and prompts each seat
to hit an F key (F1 first seat, F2 second seat, etc) and click a mouse
button and it associates the relevant devices to the proper session.

So now I have two instances of roverlog and all the associated servers
all running on one box .. hopefully we'll have fewer 'unrequested
reboots' due to the voltage dipping too low too soon into a stop in
June ;)

Some linky goodness:
Userful: http://www.userful.com
Multiseat summary: http://en.wikipedia.org/wiki/Multiseat
x.org multiseat wiki: http://wiki.x.org/wiki/Development/Documentation/Multiseat
MDM: http://wiki.c3sl.ufpr.br/multiseat/index.php/Mdm

de w1rt/john