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<WRAP centeralign round graybg box 96%>
<WRAP muchbigger>PREPARATION FOR MULTI-SEAT LINUX</WRAP>
<WRAP bigger>John T. Rine</WRAP>
</WRAP>
======Objective======
The object of this project is to set up and verify a multi-seat Linux configuration (one machine, many users).\\
======Materials/Reading/Prerequisites======
To do this project, you will need to have successfully completed:

  * Linux/*BSD Desktop Install
The materials required for this project are:\\

^Description^Quantity^
|PC to be multiseat host|1|
|LCDs|multiple|
|keyboards|multiple|
|mice|multiple|
|Linux Desktop install CD|1|
|USB docking stations|multiple|

======Background======
Lately, computing has concerned itself with the idea of a single computing resource allocated to a single user. However, with this approach, computing resources are usually wasted. There are exceptions to the one resource per user rule, a multi-tasking system for example, allows for multiple logins, there can still only be one physical user at the computer's main console, however. Multi-seat Linux allows many users to simultaneously share any single Linux PC.\\
According to the Web page from which the pictures and instructions were taken, a multi-seat configuration "is great for education, libraries, internet cafes, etc — anywhere where you have clusters of client machines with light 3D/video app demands, and want the simplicity and savings of just one server machine with many terminals connected."\\
======Requirements/Functionality/Analysis======
**Requirements**\\
The instructor's requirements for this project are:\\
Configure and document the process of setting up a Linux machine to serve as the host machine to support multiple physical users.\\
\\
**Functionality**\\
Regarding this project, once the setup and installation are complete, the instructor asks the student to explore the following functionality:\\
  * graphical login on each head
  * no interference between seats
  * administration
    * adding new software
    * configuring settings for all users
    * screen capture by administrator
    * screen broadcasting
  * individual USB flash drive access
  * per-seat audio
\\
**Analysis**\\
Regarding this project, the instructor asks the student to lookout for the following things:\\
  * How is overall CPU load with respect to the number of heads?
    * idle
    * active
  * Is there a sweet spot with regards to number of seats and host hardware?
\\
If possible, the instructor wants the student to try the configuration with both a 32-bit machine and a 64-bit machine (how well can the older 32-bit machine handle the load, how much more work can the newer 64-bit machine adequately handle?).\\
\\
======Procedure======
{{:user:jr018429:portfolio:2009-09-22-195134-fourseats.jpg|}}\\
The photos both above and below and the instructions below were taken from http://plugable.com/2009/11/16/setting-up-usb-multiseat-with-displaylink-on-linux-gdm-up-to-2-20/. Please see the reference section. \\
\\
**1. DisplayLink framebuffer driver**\\
udlfb is in the staging tree of Linux kernels 2.6.32 and later. We'll install the latest version here. First, make sure you have git installed with "sudo apt-get install git-core", and create a directory which will host all the source code you download with git (e.g. ~/git/).
<code>
sudo apt-get install module-assistant
sudo module-assistant prepare
git clone http://git.plugable.com/webdav/udlfb/
cd udlfb
make
sudo make install
sudo depmod -a
</code>
Now, when you plug in a DisplayLink device, you should see a "green screen" as the driver successfully loads and sets the graphics mode to match your monitor.\\
\\
**2. DisplayLink X server**\\
This will get the X server installed, ready for use by later scripts.\\
<code>
sudo apt-get install pkg-config xorg-dev
cd ~git
git clone http://git.plugable.com/webdav/xf-video-udlfb/
cd xf-video-udlfb
./configure
make
sudo make install
</code>
\\
We now need to create or modify a few scripts and configuration files. You'll need to use sudo to edit files in these system directories. You can cut/paste the text below, or download the files with "git clone http://git.plugable.com/webdav/misc-udlfb/" and copy each to the right location, and fix up ownership and permissions on the files.\\
\\
**3. udev script**\\
Create a file called /lib/udev/rules.d/50-usbseat.rules owned by user root, with the following contents.\\
<code>
# set all DisplayLink devices to configuration 1
# see http://libdlo.freedesktop.org/wiki/DeviceQuirks for more info
ATTR{idVendor}=="17e9", ATTR{bConfigurationValue}=="2", RUN="/bin/echo 1 > /sys%p/bConfigurationValue"
 
# aliases for display, kbd, mouse attached to specific hubs
 
KERNEL=="fb*",SUBSYSTEMS=="usb",PROGRAM="/bin/cat /sys/%p/../../../devnum",SYMLINK+="usbseat/%c/display",RUN+="usbseat.sh %c"
KERNEL=="mouse*", SUBSYSTEMS=="usb", ATTRS{bInterfaceClass}=="03", ATTRS{bInterfaceProtocol}=="02", PROGRAM="/bin/cat /sys/%p/../../../../../devnum",SYMLINK+="usbseat/%c/mouse",RUN+="usbseat.sh %c"
KERNEL=="event*", SUBSYSTEM=="input", ATTRS{bInterfaceClass}=="03", ATTRS{bInterfaceProtocol}=="01",PROGRAM="/bin/cat /sys/%p/../../../../../devnum",SYMLINK+="usbseat/%c/keyboard",RUN+="usbseat.sh %c"
KERNEL=="control*", SUBSYSTEM=="sound", SUBSYSTEMS=="usb", PROGRAM="/bin/cat /sys/%p/../../../../../devnum", SYMLINK+="usbseat/%c/sound"
 
# Handle when keyboard and mouse are one more hub downstream. Relying on pnp order to have already set up mouse, keyboard on upstream hub if we're daisy-chaining
KERNEL=="event*", SUBSYSTEM=="input", ATTRS{bInterfaceClass}=="03", ATTRS{bInterfaceProtocol}=="01",PROGRAM="/bin/cat /sys/%p/../../../../../../devnum",SYMLINK+="usbseat/%c/keyboard",RUN+="usbseat.sh %c"
KERNEL=="mouse*", SUBSYSTEMS=="usb", ATTRS{bInterfaceClass}=="03", ATTRS{bInterfaceProtocol}=="02", PROGRAM="/bin/cat /sys/%p/../../../../../../devnum",SYMLINK+="usbseat/%c/mouse",RUN+="usbseat.sh %c"
</code>
\\
The udev subsystem will run this script automatically each time a USB device is attached.\\
\\
**4. usbseat.sh script**\\
Create a file /lib/udev/usbseat.sh owned by user root with the following contents. Make sure to "sudo chmod a+x" to make the file executable.\\
<code>
#!/bin/bash
# takes the "seat number" as parameter $1
# the seat number is the kernel device id of the hub the seat's devices are sitting off of
# called once for every usb device that MIGHT be part of a seat, when they arrive or remove 
 
if [[ !(-n `/bin/pidof gdm`) ]]; then
    exit 0
fi
 
seat_running=`/usr/bin/gdmdynamic -l | /bin/sed -n -e "/:$1,/p"`
 
# $ACTION environment variable is set by udev subsystem
case "$ACTION" in
	'remove')
		if [[ -n "{$seat_running}" ]]; then
			/usr/bin/gdmdynamic -v -d $1
		fi
		;;
	*)
                # A device which might be part of a seat has been added
 
		# if we already have a running seat for this #, exit
		if [[ -n "${seat_running}" ]]; then
			exit 0
		fi
 
		if [[ -e /dev/usbseat/$1/keyboard && -e /dev/usbseat/$1/mouse && -e /dev/usbseat/$1/display ]]; then
 
			# We have a newly complete seat. Start it.
			TMPFILE=`/bin/mktemp` || exit 1
			/bin/sed "s/%ID_SEAT%/$1/g" < /lib/udev/usbseat-xf86.conf.sed > $TMPFILE
			/usr/bin/gdmdynamic -v -t 2 -s 1 -a "$1=/usr/X11R6/bin/X -br :$1 -audit 0 -nolisten tcp vt07 -config $TMPFILE"
			/usr/bin/gdmdynamic -v -r $1
		fi
		;;
esac
 
exit 0
</code>
\\
**5. X config file**\\
Create file /lib/udev/usbseat-xf86.conf.sed with contents\\
<code> 
Section "ServerFlags"
	Option	"AutoEnableDevices"	"false"
	Option	"AutoAddDevices"	"false"
	Option  "DefaultLayout"		"seat"
	Option	"DontZoom"		"true"
	Option	"DontZap"		"true"
	Option	"AllowMouseOpenFail"	"yes"
EndSection
 
Section "Module"
	Load "ddc"
EndSection
 
Section "Files"                                                                                                              
    ModulePath      "/usr/lib/xorg/modules"
    ModulePath      "/usr/local/lib/xorg/modules"
EndSection
 
Section "Device"
	Identifier "dl"
	driver	   "displaylink"
	Option "fbdev"	"/dev/usbseat/%ID_SEAT%/display"
EndSection
 
Section "InputDevice"
	Identifier "keyboard"
	Driver	"evdev"
	Option	"CoreKeyboard"
	Option	"Device"	"/dev/usbseat/%ID_SEAT%/keyboard"
	Option	"XkbModel"	"evdev"
	Option	"XkbLayout"	"us"
EndSection
 
Section "InputDevice"
	Identifier "mouse"
	Driver	"mouse"
	Option	"CorePointer"
	Option	"Protocol" "ImPS/2"
	Option	"Device"	"/dev/usbseat/%ID_SEAT%/mouse"
        Option  "Buttons" "5"
	Option	"ZAxisMapping" "4 5"
EndSection
 
Section "Monitor"
	Identifier "monitor"
EndSection
 
Section "Screen"
	Identifier "screen"
	Device "dl"
	Monitor "monitor"
EndSection
 
Section "ServerLayout"
	Identifier "seat"
	Screen	0 "screen" 0 0 
	InputDevice "keyboard" "CoreKeyboard"
	InputDevice "mouse" "CorePointer"
EndSection
</code>
\\
**6. fbcon workaround**\\
[update: this step is no longer needed with the latest udlfb from git or in kernels 2.6.37+]\\
\\
fbcon is a standard Linux kernel module, which aggressively assumes it can open any framebuffer device and take it over for use as a text terminal. Unfortunately, that's not what we want if we're going to be using that framebuffer to run its own X server. So we need to add a file /etc/modprobe.d/fbcon.conf to disable fbcon and leave our framebuffers free for other uses.\\
<code>
blacklist font
blacklist tileblit
blacklist bitblit
blacklist fbcon
</code>
This file will not take effect until you run\\
<code>
sudo update-initramfs -u
</code>
\\
Now, when you reboot and run "lsmod" you should not see fbcon in the loaded modules. And in /sys/class/graphics you should see fb0, instead of fbcon.\\
\\
**7. xrandr workaround**\\
[update: this workaround is not needed when running xf86-video-fbdev or with recent displaylink X servers with this patch]\\
\\
The DisplayLink X server currently has limited RANDR support, but later versions of GDM assume better. So for the time being, a workaround is required to get GDM applications (including gdmlogin) to display properly within the actual screen area -- otherwise they tend to think the screen has a strange rotation, and display themselves completely off it.\\
\\
Add these lines into /etc/gdm/Init/Default, right after the definition of gdmwhich()\\
<code>
XRANDR=`gdmwhich xrandr`
if [ "x$XRANDR" != "x" ]; then
  $XRANDR -o 0
fi
</code>
\\
**8. /etc/rc.local script**\\
Add the following lines to your /etc/rc.local script to check for attached usb terminals that were attached (at boot), and udev found them before GDM was running.\\
<code>
oldIFS=$IFS
IFS=/
for seat in /dev/usbseat/*; do
	set $seat
	/lib/udev/usbseat.sh $4
done
IFS=$oldIFS
</code>
\\
**9. /etc/init.d/gdm patch**\\
In recent versions of X, the system largely assumes that you'll only run one X server, and it will own all devices. So to support multiseat with multiple X servers easily, we need to have two configurations: normal (using only your primary graphics), and multiseat (where your primary graphics isn't used). We do this by detecting whether you have a USB terminal attached and configured, and if so coming up with a different gdm configuration.\\
\\
Add these lines to your /etc/init.d/gdm script, just after the section to "Allow cdd to override the config" (around line 35).\\
<code>
# Allow usbseat to override the config
if [ -f /etc/gdm/gdm-usbseat.conf ]; then
	for usbseat in /dev/usbseat/*; do
		seatid=${usbseat##*/}
		if [ -e "/dev/usbseat/$seatid/keyboard" -a -e "/dev/usbseat/$seatid/mouse" -a -e "/dev/usbseat/$seatid/display" ]; then
			CONFIG_FILE="--config=/etc/gdm/gdm-usbseat.conf"
		fi
	done
fi
</code>
\\
**10. Create /etc/gdm/gdm-usbseat.conf**\\
This is the alternative gdm.conf that will be used when a USB terminal is present at boot:\\
<code>
[daemon]
DynamicXServers=true
FlexibleXServers=0
Greeter=/usr/lib/gdm/gdmgreeter
 
[security]
 
[xdmcp]
 
[gui]
 
[greeter]
 
[chooser]
 
[debug]
 
[servers]
0=inactive
</code>
\\
{{:user:jr018429:portfolio:2009-09-22-200342-edubuntu.jpg|{{:user:jr018429:portfolio:2009-09-22-200342-edubuntu.jpg|}}\\
Now, when you boot with USB terminal(s) attached, graphical logins will come up on all of those, while your primary display will remain a text console.\\

======References======
  * http://lab46.corning-cc.edu/haas/spring2011/hpc0/projects/multiseat
  * http://plugable.com/2009/11/16/setting-up-usb-multiseat-with-displaylink-on-linux-gdm-up-to-2-20/
  * http://linuxgazette.net/124/smith.html
  * http://en.wikipedia.org/wiki/Multiseat_configuration
  * http://linuxagora.com/vbforum/showthread.php?p=3710
  * http://www2.userful.com/
    * http://www.userful.com/products/userful-multiseat-linux
  * http://www.oreillynet.com/onlamp/blog/2005/12/multiseat_x_under_linux.html
  * http://blog.chris.tylers.info/index.php?/archives/14-Multiseat-X-Under-X11R6.97.0.html
  * http://www.linuxtoday.com/it_management/2009010800335OSBZDP
  * http://www.x.org/wiki/Development/Documentation/Multiseat
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