一台主机接多套键盘鼠标显示器，实现多人共用一台电脑

是不是场面很震撼，大学时就梦想着能一个宿舍的共用一台电脑了(那时候穷啊，刚开始宿舍就一台电脑啊！)。看看人家是怎么做到的：

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

Introduction
A 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.

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（http://www.linuxtoys.org/multiseat/hydra_hang.txt）. 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.

DP: 生活的脚步，技术的点滴...

一台主机接多套键盘鼠标显示器，实现多人共用一台电脑

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