[TMG] accidentally found 6-headed super computer using linux few second ago

Sat Mar 14 04:31:39 ICT 2009

It has serious bug in new Xorg made nv card to kick out usb mouse under 24 
color depth.

I try to search problem w/o need to reduce color depth to 16 (no problem)
In doing so, I found below article accidentally.

It completely solve class room problem at near zero cost and save space 
more than my decentralizing computer. BUT idea on seat around table are 
identically copy from me.

My better featured are old pc at home also become super computer.

The choice is yours,
zxc555

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Build a Six-Headed, Six-User Linux System
By Bob Smith

Introduction
Six users on one computerA Multi-Seat Linux Box: This tutorial shows how 
to build a multi-head, multi-user Linux box using a recent distribution of 
Linux and standard USB keyboards and mice. Xorg calls this arrangement a 
"multi-seat" system.
Advantages of a Multi-Seat System:  The advantages of multi-seat systems 
in schools, Internet cafe's, and libraries include more than just saving 
money. They include much lower noise pollution, much less power 
consumption, and lowered space requirements. For many applications power 
and noise budgets are as important as initial cost.
Requirements: To build a multi-seat system you need a video adapter, 
keyboard, and mouse for each seat. For six seats, you'll also need a 
motherboard with an AGP slot and five available PCI slots. In our test 
system we used USB keyboards and mice exclusively, but you can use a PS/2 
keyboard and mouse for one seat if you wish.
Xorg 6.9 or later is required, but this already ships with many of the 
major distributions. Our test system uses the free version of Mandriva 
2006 and we did not rebuild the kernel or install any additional packages.

Overview
  We divide the implementation of a multi-seat system into five main steps:
Select and Install the Hardware
Install Linux
Record Hardware Configuration
Modify xorg.conf
Modify gdm.conf
  After installing the hardware and installing Linux, we read the hardware 
configuration from the lspci command from from the /proc/bus/input/devices 
file. Most of the effort in setting up a multi-seat system is in 
transcribing the hardware information into the xorg.conf file.

Step 1: Select and Install the Hardware
Selecting the Hardware:  There are few set rules dictating what hardware 
to use in your multi-seat system. Of necessity, some of the keyboards and 
mice need to use USB, but there is no minimum CPU or memory requirements. 
We suggest building and testing a multi-seat system using a computer that 
you already have, and use the test results to help scale your hardware 
requirements. You may be surprised how modest the CPU and memory 
requirements are for a multi-seat system that is used only for web 
browsing.
  If possible, try to use accelerated video cards, but for increased 
reliability, avoid video cards with on-board fans. Use recent video cards; 
older video cards often have a problem sharing the PCI bus. We've had good 
luck with nVidia cards but you can try recent cards from other 
manufacturers too.
Hardware for our test system:  For our system we chose to use video cards 
based on the nVidia MX4000 chipset. They are accelerated, have no fans, 
and it was nice having one driver for all six video cards. The downside of 
nVidia is that the driver is closed source and you need to download and 
install it. If you use an nVidia card, be sure to check their web site for 
the recommended BIOS settings for your cards.
  A typical PC We used an ECS 755-A2 motherboard with an AMD64-3200 
processor and 1 GB of RAM. Our power supply is a CoolMax 140mm Power 
Supply and the CPU heat sink is a Thermaltake "Sonic Tower". During our 
testing we added a low noise fan to cool the video cards. Airflow is in at 
the bottom, past the video cards, up past the CPU cooler and out through 
the power supply. This airflow seemed to work pretty well. At quiescence, 
the CPU temperature was 31C, rising to only 38C after fifteen minutes of 
kernel compile. The current from the mains at quiescence was 0.25 amps, 
and during a kernel compile it was 0.35 amps.
  You will probably need some USB hubs to connect all of the keyboards and 
mice. One problem to think about before permanently installing the 
hardware is cable management. Seven power cords, six monitor cables, three 
USB hubs, six keyboard cables, and six mice cables: that is a lot of 
cabling!

Step 2: Install Linux
  Multi-seat capability is provided by Xorg 6.9/7.0 which already ships 
with most of the major distributions. When you install Linux, you might 
want to install all of the window managers including fluxbox and twm. If 
you are going to use the nVidia drivers, be sure to install the kernel 
source too.
  Do the installation with all of the hardware connected and powered up. 
Mandriva did a great job detecting and configuring all six of our video 
heads. Select a default run level of 3 so that X does not start 
automatically after boot. You can check the installation by logging in and 
running startx. If all has gone well you should be able to move your mouse 
across all six monitors.
  Mandriva makes up to ten entries in the /dev/input directory. We needed 
twelve since we had six keyboards and mice. We increased the limit to 
sixteen by changing the line in /etc/udev/ruled.d/50-mdk.rules from:
     KERNEL=="event[0-9]*", NAME="input/%k", MODE="0600"
to:
     KERNEL=="event[0-9a-f]*", NAME="input/%k", MODE="0600"

Step 3: Record Hardware Configuration
  All hardware in our computer has a name that distinguishes it from 
similar hardware in the computer. In this step we record the names for 
each of our video heads, keyboards, and mice. Let's start with the video 
cards.
  Video cards are identified by their address on the PCI bus. We can list 
the hardware on the PCI buses using the lspci command. On our test system, 
the lspci command gives the following result:
lspci | grep VGA
00:09.0 VGA compatible controller: nVidia Corporation NV18 [GeForce4 MX 
4000 AGP 8x] (rev c1)
00:0a.0 VGA compatible controller: nVidia Corporation NV18 [GeForce4 MX 
4000 AGP 8x] (rev c1)
00:0b.0 VGA compatible controller: nVidia Corporation NV18 [GeForce4 MX 
4000 AGP 8x] (rev c1)
00:0c.0 VGA compatible controller: nVidia Corporation NV18 [GeForce4 MX 
4000 AGP 8x] (rev c1)
00:0d.0 VGA compatible controller: nVidia Corporation NV18 [GeForce4 MX 
4000 AGP 8x] (rev c1)
01:00.0 VGA compatible controller: nVidia Corporation NV18 [GeForce4 MX 
4000 AGP 8x] (rev c1)

  The bus address is the first field in the lines above. The number before 
the colon identifies which PCI bus (computers often have more than one), 
and the second number gives the card address on the bus. You will need to 
know these addresses to build the xorg.conf configuration file.
  The mice are easy to locate. Each mouse has an entry in the /dev/input 
directory. An ls can identify the mice.
ls /dev/input/mouse*
/dev/input/mouse0  /dev/input/mouse2  /dev/input/mouse4
/dev/input/mouse1  /dev/input/mouse3  /dev/input/mouse5

  The keyboards are identified as a /dev/input/eventN file. Do a more of 
/proc/bus/input/devices. Each keyboard will have an entry that specifies 
the event file. The following two entries are for the first two keyboards 
in our system.
more /proc/bus/input/devices

I: Bus=0003 Vendor=046e Product=530a Version=0001
N: Name="BTC Multimedia USB Keyboard"
P: Phys=usb-0000:00:03.3-4.2.1/input0
H: Handlers=kbd event6
B: EV=120003
B: KEY=1000000000007 ff87207ac14057ff febeffdfffefffff fffffffffffffffe
B: LED=1f

I: Bus=0003 Vendor=046e Product=530a Version=0001
N: Name="BTC Multimedia USB Keyboard"
P: Phys=usb-0000:00:03.3-4.4.1/input0
H: Handlers=kbd event7
B: EV=120003
B: KEY=1000000000007 ff87207ac14057ff febeffdfffefffff fffffffffffffffe
B: LED=1f

  A table is a nice way to view all of the above information.
Seat
Video Card
Keyboard
(/dev/input/)
Mouse
(/dev/input/)
0  00:09:0  event6  mouse0
   1  00:10:0  event7  mouse1
   2  00:11:0  event8  mouse2
   3  00:12:0  event9  mouse3
   4  00:13:0  event10  mouse4
   5  01:00:0  event11  mouse5

    Note the slight change in how the video cards are addressed. Also, 
you'll find the numbering of the keyboards and mice easier if you plug 
each mouse into the same hub as its corresponding keyboard. Don't worry 
too much about matching the video head to the keyboard. After setting 
everything up you can move the monitors or the keyboards around as needed.

Step 4: Build xorg.conf
  The xorg.conf file has sections to describe keyboards, mice, video cards, 
monitors, screens, and seats. Most of the work in setting up a multi-seat 
system is correctly copying the information in the above table into the 
appropriate section of the xorg.conf file. Shown below is our 
configuration for seat 5. You should be able to use this configuration as 
a prototype for your additional seats. Note the places where the keyboard, 
mouse, and video card information is located. Since we were borrowing 
monitors for our test, we forced all of the monitors to be flat panel 
displays with a 1024 by 768 resolution.
# Seat 5
Section "InputDevice"
     Identifier     "Keyboard5"
     Driver         "evdev"
     Option         "Device" "/dev/input/event11"
     Option         "XkbModel" "pc105"
     Option         "XkbLayout" "us"
     Option         "XkbOptions" "compose:rwin"
EndSection

Section "InputDevice"
     Identifier     "Mouse5"
     Driver         "mouse"
     Option         "Protocol" "ExplorerPS/2"
     Option         "Device" "/dev/input/mouse5"
     Option         "ZAxisMapping" "6 7"
EndSection

Section "Device"
     Identifier     "device5"
     Driver         "nvidia"
     VendorName     "NVIDIA Corp."
     BoardName      "NVIDIA GeForce4 (generic)"
     BusID          "PCI:0:13:0"
EndSection

Section "Monitor"
     Identifier     "monitor5"
     ModelName      "Flat Panel 1024x768"
     HorizSync       31.5 - 48.5
     VertRefresh     40.0 - 70.0
     ModeLine       "768x576" 50.0 768 832 846 1000 576 590 595 630
     ModeLine       "768x576" 63.1 768 800 960 1024 576 578 590 616
EndSection

Section "Screen"
     Identifier     "screen5"
     Device         "device5"
     Monitor        "monitor5"
     DefaultDepth    24
     SubSection     "Display"
         Virtual     1024 768
         Depth       24
     EndSubSection
EndSection

Section "ServerLayout"
     Identifier     "seat5"
     Screen      0  "Screen5" 0 0
     InputDevice    "Mouse5" "CorePointer"
     InputDevice    "Keyboard5" "CoreKeyboard"
EndSection

  There is a simple trick to help verify that all the numbers in the 
xorg.conf file are right -- pass the file through sort and uniq.

    cat /etc/X11/xorg.conf | sort | uniq

  The output of the above command string will make obvious any errors in 
numbering the various keyboards and such.
Testing Your Xorg.conf File:  It is a good idea to test your configuration 
and to sort out the keyboards and mice by bringing up the heads one at a 
time. Login remotely so that you are not using any of the video heads. 
Enter the following commands for each of the six heads (0 to 5). (The 
commands below are for head 5.)

X -novtswitch -sharevts -nolisten tcp -layout seat5 :5 &
xterm -display :5 &

  If the above command fails, examine the error messages and check the 
xorg.conf file. If the command succeeds, use the xterm to help identify 
which keyboard and mouse go to which head. The keyboards, mice, and video 
cards are enumerated in the same order on every boot, so you will only 
have to move things around during the initial set up.
  The above commands might be sufficient if you don't need user logins. For 
example, a six headed kiosk might need only X and a web browser on each 
head.

Step 5: Modify gdm.conf
  If you want user logins you will need to modify the configuration for 
your preferred display manager. The directions given here are for gdm but 
the changes are very similar for kdm, or for the X display manager, xdm.
  Modify the [servers] section near the bottom of the /etc/X11/gdm/gdm.conf 
file to tell gdm which X servers to start. The lines should be:
0=Standard0
1=Standard1
2=Standard2
3=Standard3
4=Standard4
5=Standard5

  You need to tell gdm how to start the X server on each head. The lines to 
do this are:
[server-Standard5]
name=Standard server
command=/usr/X11R6/bin/X -nolisten tcp -novtswitch -sharevts -layout seat5
flexible=true

  You'll need a section like the above for each head. The server name, 
"Standard5" in the above example, must match the name given in the 
[servers] section. Customize the X command line options to meet the 
requirements of your particular system.
  Once everything is configured, you should be able to start graphical 
logins by switching to runlevel 5.
telinit 5

  If everything works, make the default runlevel 5 by editing /etc/inittab 
or by setting it using drakconf.

Test Results, Costs, and Problems
Performance Results:  Between resets, we found performance to be excellent 
for six users doing typical PC tasks, including web browsing, email, word 
processing, and games. The accelerated graphics cards seemed to do most of 
the work so that even arcade style games and web-based video did not put 
much of a load on the CPU. If "3200" is an accurate assessment of the 
performance of the AMD64-3200, then a CPU with a performance of "1600" 
would have been more than sufficient.
Cost:  Not including the monitor, each seat in our system cost about $67. 
This includes $40 for the MX4000 based video card, $20 for a USB keyboard, 
$5 for a USB mouse, and $2 for half of a USB hub. Our test system uses 
expensive keyboards that have a built-in USB hub which we intended for per 
user flash disks or audio players.
  The shared part of our system cost about $520. This includes $180 for the 
CPU, $50 for the motherboard, $90 for RAM, and $50 for the CPU heat sink. 
The case, power supply, and disk drive had a combined cost of about $150.
  We give these prices just for comparison. You may find lower prices that 
these and we'd certainly recommend that you replace our $230 CPU and 
motherboard with an Athlon 2800+ set that costs about $80. We have not 
included the cost of the monitors since these prices are in free fall and 
your particular needs and tastes may dictate what you spend.
Problems:  Did you catch the phrase "between resets" above? While the 
system worked very well, it was extremely unstable. In particular, we got 
a kernel oops fairly often when we logged out. A syslog trace of one such 
oops is available  here. We've tried several things to fix this problem 
including:

turning APIC off and on
reducing the number of heads
trying the 'nv' and 'vesa' drivers
using NoInt10
upgrading to the official X11R6.9 release
upgrading to the 2.6.15 kernel
using xdm and fvwm instead of gdm and Gnome
  The problem persists. Please let bsmith at linuxtoys dot org know if you 
have any ideas that might help fix this problem.
  A much less severe problem is that some programs assume that there is a 
single user on the PC. Screen savers can take a lot of CPU power and both 
KDE and Gnome complain if they don't have audio output. Any shared 
resource, such as audio or a CD burner, can be a problem.
  Longer term, we will need to address security issues surrounding 
multi-seat computers. Whether from students or cafe patrons, these systems 
are going to come under deliberate, malicious attack. Can we trust KDE and 
Gnome to withstand such attacks?

Summary
  A multi-head, multi-user Linux system is now possible using commodity PC 
hardware and standard Linux distributions. Multi-seat Linux PCs seem 
inevitable given the potential savings in cost, noise, and power.

Further Reading
Chris Tyler's page:  Chris Tyler provided support at almost every step of 
the way in this project. His web site has a HOWTO that also describes how 
to set up a multi-seat system. Chris is something of an expert in X and 
I'm looking forward to his next book which will contain some of the 
material presented here. Chris' web site is at:
      http://blog.chris.tylers.info/
Xorg man pages:  Xorg provides a full set of manual pages that describe 
the xorg.conf file and all of the commands used in getting X-Windows to 
run. The manual page for xorg.conf is at:
      http://wiki.x.org/X11R6.9.0/doc/html/xorg.conf.5.html
  The manual pages for the X commands are at:
      http://wiki.x.org/X11R6.9.0/doc/html/manindex1.html