How to Build a Multi-Seat Ubuntu System

Introduction

This article shows how to install Ubuntu from DVDs, how to configure Ubuntu to use multiple video cards for one user, and, finally, how to configure X to have one user per video head. This is a follow-on to an earlier article presented here. The information in the earlier article is still valid and so this article focuses on the installation and initial configuration of Ubuntu.

Overview

1. Install the Hardware
2. Install Ubuntu from DVD
3. Configure a Single-user Multi-head System
4. Modify xorg.conf
5. Modify gdm.conf

Step 1: Install the Hardware

After testing many video cards and even more drivers we have settled on an accelerated, fanless video card using the nVidia MX4000 chipset. While nearing end-of-life, these cards are still available in both AGP and PCI versions.

You need a keyboard and mouse for each seat. Typically the original seat has a PS2 keyboard and mouse, and each additional seat has a USB keyboard and mouse.

Step 2: Install Ubuntu from DVDs

Internet access at Yared's school is limited to an expensive and slow dial-up account. To overcome this limitation we've sent him a six DVD set of Ubuntu 7.04 which we bought from The Linux Store. The procedure given below assumes the reader has no Internet access and is still somewhat new to Linux. High bandwidth, experienced Linux users should skip this step.

• Insert the Boot/Install CD and reset the PC
• A graphical UI should appear. Double-click the "Install" icon.
• Select the language, time zone, and keyboard.
• Partition the disk per your requirements. If you're new to Linux you might want to select "Guided - Use Entire Disk"
• After setting up the disk partitions you will be presented with a summary screen. Select "Install".
• After the installation, remove the DVD and reboot the PC.

Since we are not using the Internet we need to configure Synaptic to look at the DVDs and not at any of the Ubuntu download sites.

• Login and open System->Administration->Software_Sources.
• Uncheck the five options in the top panel labeled "Downloadable from the Internet". Under "Updates", uncheck the option labeled "Check for Updates".

We need to tell Synaptic what packages are each of the DVDs. There's a bug in this distribution of Ubuntu 7.04 in that DVDs are mounted under /media/CDROM but Synaptic expects to find them under /cdrom. We can create a link but the system doesn't always mount DVDs under /media/CDROM. It is easier to do register each DVD manually using the steps below.

• Open a terminal window and do an 'sudo bash' to gain root access.
• Insert the Boot/Install DVD. Ubuntu will detect that this DVD contains packages and ask if you want to run the package manager (Synaptic). Say "Cancel" to this request. Close the File Browser window that opens as well.
• Do a 'mount' command in the terminal to see where the DVD was mounted.
• Do a 'apt-cdrom add -m -d '. This scans the DVD and associates this DVD with the packages it contains.
• Do a 'umount ' and 'eject' to eject the DVD.
• Repeat the above three steps for each of the DVDs in the set. Enter the name of the DVD when asked to.

You can verify that the above steps worked by opening Synaptic. Use System->Administration->Synaptic_Package_Manager. The footer at the bottom of the window should report that something like 21,000 packages are available for installation.

When asked, you might want to apply the updates the system finds on the last DVD. Not that you need them, but the system will keep pestering you to install them.

Step 3: Configure a Single-user Multi-head System

At this point we could refer to the earlier article to configure the system for multi-user use. However Ubuntu can make this a little easier by detecting and configuring the video cards for us. The procedure below describes how to do this.

• Run Synaptic and install the following packages:
     linux-restricted-modules-2.6.20-15-386
     nvidia-glx
  The above will also install a new kernel to satisfy dependencies.
• Open a terminal window and run 'sudo nvidia-xconfig'.
  This converts the /etc/X11/xorg.conf file for use with the new nVidia drivers.
• Reboot. The nVidia logo should appear briefly as the system comes up.
• Open a terminal window and run 'sudo nvidia-settings'. Select the Display Configuration" and configure each of the system's video heads. (I generally configure all heads for 1024x768 since I know all of my monitors can handle this.)
• Select "Enable Xinerama" and then "Save to X Configuration File".
• Reboot. This time all the heads should flash the nVidia logo.
• Login and note that your mouse can now travel across all the screens.

Step 4: Modify xorg.conf

Most of the system changed needed to build a multi-seat system occur in the xorg.conf file. Here are the steps to modify the file.

• Attach the extra USB mice and keyboards. Test the hardware by moving each mouse. The cursor should move for any movement of any mouse. The same is true of the keyboards. Any key entered on any keyboard should appear on the screen.
• Before modifying xorg.conf we need to know the names of the mice and keyboards on the system. You can see the names of the mice with the command:
  ls /dev/input/mouse*
  The first mouse, called mouse0, is not really an attached mouse and you can ignore it. The mice name mouse1 and above are the real mice.
• You can get the name of the keyboards from the following command:
  more /proc/bus/input/devices
  Note the event ID for each keyboard handler.

  I: Bus=0003 Vendor=046e Product=530a Version=0001
  N: Name="BTC Multimedia USB Keyboard"
  P: Phys=/input0
  S: Sysfs=/class/input/input3
  H: Handlers=kbd event3
  B: EV=120003
  B: KEY=7 ff87207ac14057ff febeffdfffefffff fffffffffffffffe
  B: LED=1f

• The big difference between a multi-head system and a multi-user system is in the xorg.conf file. Open a terminal window and 'sudo bash' to become root. Do a 'cd /etc/X11/' to change directory to /etc/X11/.
• Save your existing version of xorg.conf. If something goes wrong you'll want to be able to use it to test the hardware and to get back to a known working configuration.
      cp xorg.conf xorg.conf.multihead
• You need to tell X11 about each seat on your multi-user system. Each seat has a keyboard, a mouse, a video device, a monitor, a screen, and a layout. Your existing multihead xorg file should have correct entries for all of the devices, monitors, and screens. It will also have samples for the keyboard, mice, and server layout entries. You need to create new entries for the additional keyboards, mice, and layouts.
• Open the xorg.conf file with your favorite editor. Locate the keyboard section. Change the driver to 'evdev' and add the device line to the keyboard section. Now copy and paste this section. Edit the new section to give it a new keyboard number and to use the event handler we found in the above steps. Do this for each new keyboard. Sample keyboard sections are shown below:
  

  Section "InputDevice"
      # generated from default
      Identifier     "Keyboard0"
      Driver         "evdev"
      Option         "Device" "/dev/input/event1"
  EndSection
  
  Section "InputDevice"
      # generated from default
      Identifier     "Keyboard1"
      Driver         "evdev"
      Option         "Device" "/dev/input/event3"
  EndSection
  

• Do the same kind of update/copy/paste for each of the mice. In each mouse section change the Device to /dev/input/mouseX, where X is one of the values determined by looking at 'ls /dev/input/mouse*'. Sample mouse sections are shown below.
  

  Section "InputDevice"
      # generated from default
      Identifier     "Mouse0"
      Driver         "mouse"
      Option         "Protocol" "auto"
      Option         "Device" "/dev/input/mouse1"
      Option         "Emulate3Buttons" "no"
      Option         "ZAxisMapping" "4 5"
  EndSection
  
  Section "InputDevice"
      # generated from default
      Identifier     "Mouse1"
      Driver         "mouse"
      Option         "Protocol" "auto"
      Option         "Device" "/dev/input/mouse2"
      Option         "Emulate3Buttons" "no"
      Option         "ZAxisMapping" "4 5"
  EndSection
  

• The server layout sections associate the different keyboards, mice, video cards, and screens into what we call a "seat". Typically the numbers for the layout, mouse, keyboard and screen all increment with each new seat. Here are the layout sections we use for our two seat system. Your layout sections should be similar.
  

  Section "ServerLayout"
      Identifier     "Layout0"
      Screen      0  "Screen0" 0 0
      InputDevice    "Keyboard0" "CoreKeyboard"
      InputDevice    "Mouse0" "CorePointer"
  EndSection
  
  Section "ServerLayout"
      Identifier     "Layout1"
      Screen      0  "Screen1" 0 0
      InputDevice    "Keyboard1" "CoreKeyboard"
      InputDevice    "Mouse1" "CorePointer"
  EndSection
  

Step 5: Modify gdm.conf

The final step in setting up your multi-seat Ubuntu PC is to tell gdm, the graphical login program, about your additional seats.

• Become root and the file /etc/gdm/gdm.conf for editing.
• Locate the "[servers]" section. On my system it is about 550 lines into the file.
• Replace the line "0=Standard" with the lines

  0=Standard0
  1=Standard1
  

• Locate the "[server-Standard]" section.
• Replace this section with the following lines

  [server-Standard0]
  name=Standard server #0
  command=/usr/X11R6/bin/X -br -audit 0 -nolisten tcp -novtswitch -sharevts -layout Layout0
  flexible=true
  
  [server-Standard1]
  name=Standard server #1
  command=/usr/X11R6/bin/X -br -audit 0 -nolisten tcp -novtswitch -sharevts -layout Layout1
  flexible=true
  

• Save and close the edit session of /etc/gdm/gdm.conf.
• Reboot your computer to switch to your new multi-seat configuration.