The Webcam HOWTO

Howard Shane

<hshane[AT]austin.rr.com>
Revision History                                                             
Revision 1.61            2005-02-21            Revised by: jhs               
Update on revived Philips Webcam driver development                          
Revision 1.6             2005-01-02            Revised by: jhs               
Errata fixed, some rewrites for readability, new chipsets and updates        
Revision 1.1             2004-01-12            Revised by: jhs               
Update for 2.6 series kernel release and info on NW802-based webcams         
Revision 1.0             2003-12-04            Revised by: JP                
Initial Release / Reviewed by TLDP                                           
Revision 0.5             2003-11-07            Revised by: jhs               
Final revision after v4l mailing list feedback                               
Revision 0.1             2003-10-12            Revised by: jhs               
Initial draft posted                                                         


This document was written to assist the reader in the steps necessary to
configure and use a webcam within the Linux operating system.

-----------------------------------------------------------------------------
Table of Contents
1. Introduction
    1.1. Copyright Information
    1.2. Disclaimer
    1.3. New Versions
    1.4. Credits
    1.5. Feedback
    1.6. Conventions Used in this Document
   
   
2. Enabling Support for Your (Webcam) Hardware in Linux
    2.1. Drivers and Modules
    2.2. Supporting the Connection Type
    2.3. Specific Webcam Models
   
   
3. Accessing the Video Device
    3.1. The Video Devices Node
    3.2. Groups and Permissions
   
   
4. Framegrabbing Applications
    4.1. Command Line Programs
    4.2. GUI(Grapical User Interface)-Based Programs
   
   
5. Troubleshooting
    5.1. Help, I have a USB webcam and don't know exactly what model it is
        and/or who the manufacturer is. What do I do?
    5.2. Help, I can't find the camera device in /dev!
    5.3. Help, I can see the camera device (both in person and as a device
        node in /dev), but I can't access it!
    5.4. Help, my camera has a driver that is source-only, i.e., has to be
        built by me! Where do I start?
    5.5. I am using Debian GNU/Linux. Is there an easier way to go through
        all this kernel compiling stuff and building of source modules?
    5.6. Help, my camera is supported by a driver that has to be patched into
        my kernel! What do I do?
    5.7. Help--as in, where can I get more of it?
    5.8. Help, I want to contribute to Video4Linux support in Linux! Who do I
        get in touch with?
   
   
A. Gnu Free Documentation License

1. Introduction

This document was written to assist the reader in setting up and configuring
a webcam, digital camera, or other video device in the Linux operating
system. It outlines how to enable the necessary kernel and/or software
support and various frame-grabber applications that can be used to access
your device. It does not discuss the differences in graphic and video
formats, the features and/or capabilities of particular devices, or the
encoding or conversion of video formats.
-----------------------------------------------------------------------------

1.1. Copyright Information

This document is Copyright 2004-2005, by Howard Shane.

Permission is granted to copy, distribute, and/or modify this document under
the terms of the GNU Free Documentation License, Version 1.2 or any later
version published by the Free Software Foundation with no Invariant Sections,
no Front-Cover Texts, and no Back-Cover Texts. A copy of the license can be
found in Appendix A.
-----------------------------------------------------------------------------

1.2. Disclaimer

No liability for the contents of this document can be accepted. Use the
concepts, examples and other content entirely at your own risk. As this is a
new edition, there may be technical or other inaccuracies that may result in
the loss of irreplaceable data. In any case, proceed with caution, and
realize that although errors are highly unlikely, the author can accept no
responsibility for them.

All copyrights are held by their respective owners, unless specifically noted
otherwise. Use of a term in this document should not be regarded as affecting
the validity of any trademark or service mark.

Naming of particular products or brands should not be seen as endorsements.
-----------------------------------------------------------------------------

1.3. New Versions

This is the fourth release.

The latest version number of this document can be found [http://www.tldp.org/
HOWTO/Webcam-HOWTO/] here.
-----------------------------------------------------------------------------

1.4. Credits

I would like to thank all of the individuals that have pioneered video
support for Linux, in particular the v4l and v4l2 teams, Gerd Knorr, and the
Metzler Brothers among others.

Also, I would like to thank Marla, who has the grace to accept my
imperfections and idiosyncrasies unconditionally, including my obsession with
projects such as this.
-----------------------------------------------------------------------------

1.5. Feedback

Please send any additions or comments pertaining to this document to the
following email address: <hshane[AT]austin.rr.com>. In particular, if you
have information about new devices or interfaces supported or errata, please
contact me so we can keep this document up-to-date!
-----------------------------------------------------------------------------

1.6. Conventions Used in this Document

The following conventions are used in this document and are outlined here for
those who may not yet have a complete understanding of how to access and
control the underlying operating system in Linux, which is usually via the
Bash shell.

First, filenames are referenced in a paragraph like so: /path/file

Commands in Linux are executed (or 'called') at the command prompt, otherwise
known as the 'command line.' If you are in the non-graphical (text-based)
environment, you will usually be presented with the Bash shell prompt which
is a dollar sign:

+---------------------------------------------------------------------------+
|   $                                                                       |
+---------------------------------------------------------------------------+

...or the hash mark:

+---------------------------------------------------------------------------+
|   #                                                                       |
+---------------------------------------------------------------------------+

...if you have logged in as root or have otherwise acquired root, or
'superuser' privileges. You can also access the Bash shell in the X window
system, otherwise known as X or X11, with an [http://invisible-island.net/
xterm/] xterm or similar X-terminal-emulator. Commands to be performed at the
Bash prompt, but referenced in a paragraph of this document, usually look
like this: do this now

Commands and/or the resulting output of commands may also be outlined with
screen output in their own paragraph or heading:

+---------------------------------------------------------------------------+
|   $  date                                                                 |
|   Sun Jul 27 22:37:11 CDT 2003                                            |
+---------------------------------------------------------------------------+

When a command is written in front of the Bash prompt (e.g., $ date above),
it is assumed the [Return] or [Enter] key has been pressed after the command,
possibly followed by the output on a new line (e.g., as in the date in the
above example).
-----------------------------------------------------------------------------

2. Enabling Support for Your (Webcam) Hardware in Linux

2.1. Drivers and Modules

For your webcam to work you will need support for the connection and support
for the actual camera hardware. Those who are already versed in kernels and
modules and how to load them should skip to Section 2.2, which addresses
support of the connection type. If you know your USB, IEEE 1394 or whatever
bus you will be connecting your camera to is already configured and working,
you should move on to the list of specific webcam hardware listed in Section
2.3.

Webcam drivers are usually available one of three ways: within the kernel, as
a compilable stand alone module, or available as a pre-compiled (packaged)
binary driver from your Linux distribution.
-----------------------------------------------------------------------------

2.1.1. Module or In-Kernel?

As a rule, often the stock kernel, or working part of the operating system,
of your initial installation may already have support for what you need. Your
Linux distribution vendor has likely enabled the most common options already,
including the bus, or connection type, and drivers for common camera models.
The driver exists either as a loadable module or within the already running
kernel.

An easy way to tell if the driver is enabled is to use the dmesg command
piped into less (for easy paging) to look for an acknowledgement that it was
loaded when your system started up:

+---------------------------------------------------------------------------+
|   $  dmesg | less                                                         |
+---------------------------------------------------------------------------+

...which may yield something like the following, depending on your hardware:

+------------------------------------------------------------------------------------------------------------------------------------+
|   Dec 18 17:35:18 localhost kernel: hub 5-0:1.0: USB hub found                                                                     |
|   Dec 18 17:35:18 localhost kernel: hub 5-0:1.0: 2 ports detected                                                                  |
|   Dec 18 17:35:18 localhost kernel: Linux video capture interface: v1.00                                                           |
|   Dec 18 17:35:18 localhost kernel: quickcam: QuickCam USB camera found (driver version QuickCam USB $Date: 2005/01/07 13:29:53 $) |
|   Dec 18 17:35:18 localhost kernel: quickcam: Kernel:2.6.7 bus:1 class:FF subclass:FF vendor:046D product:0840                     |
|   Dec 18 17:35:18 localhost kernel: quickcam: Sensor HDCS-1000/1100 detected                                                       |
|   Dec 18 17:35:18 localhost kernel: quickcam: Registered device: /dev/video0                                                       |
|   Dec 18 17:35:18 localhost kernel: usbcore: registered new driver quickcam                                                        |
+------------------------------------------------------------------------------------------------------------------------------------+

If you don't see it, the particular driver may exist as a loadable module. If
you know what that module is named, try using find; in this example we are
looking for the 'ibmcam' module:

+---------------------------------------------------------------------------+
|  $  find /lib/modules -name ibmcam.o                                      |
+---------------------------------------------------------------------------+

Note that up until the 2.4 series modules had the suffix .o; for 2.6+ series
kernels this was replaced with .ko.

You can get a list of all modules available by typing the following at the
command line:

+---------------------------------------------------------------------------+
|  $  ls -R /lib/modules/`uname -r`/kernel                                  |
+---------------------------------------------------------------------------+

Where `uname -r`, surrounded by forward tick marks, is your kernel version
number. The following output is an example of what you might find in a USB
webcam-ready kernel , where everything is loaded as a module (all but the
relevant lines have been edited for brevity):

+---------------------------------------------------------------------------+
|   ./usb: usbvideo.o usbcore.o ibmcam.o                                    |
+---------------------------------------------------------------------------+

Once you know which module your camera needs you can find out if it is
already loaded by typing the following at the command line:

+---------------------------------------------------------------------------+
|   #  lsmod                                                                |
+---------------------------------------------------------------------------+

As shown by the prompt above, you will need to have root privileges to do
this. You should get output similar to the following:

+---------------------------------------------------------------------------+
|   cdrom                  29312   0  (autoclean) [sr_mod]                  |
|   usb-ohci               17888   0  (unused)                              |
|   usbcore                56768   0  [scanner ibmcam usbvideo usb-ohci]    |
|   ibmcam                 39680   0                                        |
+---------------------------------------------------------------------------+

Most stock kernels are compiled with kmod, which enabling automatic loading
of necessary modules when the appropriate hardware is detected. It may not
always do so, however, so if you don't have the particular module you're
seeking loaded and you think the module may be available, try loading it
manually with modprobe, as in the following using the ibmcam module as an
example:

+---------------------------------------------------------------------------+
|   # modprobe -v ibmcam                                                    |
+---------------------------------------------------------------------------+

Drivers for specific webcam models, or links to project pages hosting code
for drivers, are outlined in Section 2.3. The drivers are usually available
one of three ways: within the kernel, as a compilable stand alone module, or
available as a pre-compiled binary from your Linux distribution.

If the support for your driver is not found either enabled statically within
the kernel or as a module, don't despair. Drivers for numerous models are in
the Linux kernel source (available directly from [http://www.kernel.org]
kernel.org source code repository), or in code offered separately from the
kernel that can be configured to work with your current setup as oulined in 
Section 2.1.2. If your webcam driver is available in the kernel source but
not enabled as a module or otherwise in your default system, you can either
recompile the kernel from the source code you have or obtain a new version of
the kernel source, either pre-packaged by your Linux distributor or directly
from the previous link (as a so-called "vanilla" kernel). If you are
unfamiliar with the prerequisites and procedure of compiling your own kernel,
I direct you to the [http://www.tldp.org/HOWTO/Kernel-HOWTO.html] Kernel
HOWTO for more information.
-----------------------------------------------------------------------------

2.1.2. Patching, Source-Only or Precompiled Binary?

You may find that your webcam is supported by only a kernel patch, by a
source-only driver not requiring a kernel recompile, or you may even be lucky
enough to have a distribution that makes a pre-compiled and packaged binary
driver available for your computer's architecture. The procedure involved in
the former is largely beyond the scope of this document and is probably best
outlined in the documentation available on the web page of your particular
model's driver found in Section 2.3. Some further more general documentation
on these processes are, however, addressed in Section 5
-----------------------------------------------------------------------------

2.2. Supporting the Connection Type

2.2.1. USB Webcams

If you have a USB webcam, it is likely a Linux driver has been written for
your device. There are two ways of supporting USB devices in Linux. One is
the more traditional kernel support, and the other is through libusb. For at
least one webcam category, the STV0680-based models, working libusb support
is recommended, at least according to the Sourceforge page on the subject.

Unless you know your driver requires libusb support, you should probably
stick with the more conventional in-kernel support for USB devices beginning
in Section 2.2.1.2.
-----------------------------------------------------------------------------

2.2.1.1. Libusb

Libusb is a library that allows access to the USB functions in Linux through
userspace and without the need to enable kernel support and insert modules.
Most distributions, at this point, are offering [http://
libusb.sourceforge.net/] libusb in their stable branches (and some install it
by default), so if you don't already have kernel support for USB devices,
then you may only have to install the libusb package in order to access your
device. You must have USB device filesystem support enabled in your kernel,
which most distributions do. To find out for sure, issue the following at the
command line:

+---------------------------------------------------------------------------+
|   $  cat /proc/filesystems                                                |
+---------------------------------------------------------------------------+

You should see (among others):

+---------------------------------------------------------------------------+
|   nodev    usbdevfs                                                       |
|   nodev    usbfs                                                          |
+---------------------------------------------------------------------------+

You may need to mount usbdevfs to enable it and see the device files, which
you can do at the command line with mount -t usbdevfs none /proc/bus/usb.
Don't try to use libusb while your particular kernel webcam support is
enabled either statically or the module loaded; you can only use one at at
time.

You can obtain the libusb package in .rpm, .tgz or .deb format from your
Linux distribution.
-----------------------------------------------------------------------------

2.2.1.2. Linux Kernel USB Support

Kernel support is required for USB webcam support if not using libusb
(outlined above).

For 2.2 and 2.4 series kernels, your USB webcam may require the module
usbvideo to function. This is not required in the 2.6+ series. 

For generic USB bus support in Linux, you will need USB subsystem support in
your kernel, whether usb-ohci, usb-ehci, or whatever flavor of USB driver
your system prefers. USB subsystem support has been present in the Linux
kernel since the late 2.2 series. For a more in-depth discussion of USB
support in general, I direct you to the [http://www.linux-usb.org/] Linux-usb
project site. If you want to find out which modules are loaded, at the
command line or in an xterm, type the following: 

+---------------------------------------------------------------------------+
|   #  lsmod                                                                |
+---------------------------------------------------------------------------+

As shown by the prompt above, you will need to have root privileges to do
this. You should get output similar to the following:

+---------------------------------------------------------------------------+
|   cdrom               29312   0  (autoclean) [sr_mod]                     |
|   usb-ohci            17888   0  (unused)                                 |
|   usbcore             56768   0  [scanner ibmcam usbvideo usb-ohci]       |
|   ibmcam              39680   0                                           |
+---------------------------------------------------------------------------+

If you don't have the particular module you're seeking loaded and you think
the module may be available, try loading it directly (using the usb ibmcam
module as an example):

+---------------------------------------------------------------------------+
|   #  modprobe -v ibmcam                                                   |
+---------------------------------------------------------------------------+

...at which point you should see something like the following:

+---------------------------------------------------------------------------+
|   Using /lib/modules/2.4.20/kernel/drivers/usb/ibmcam.o                   |
+---------------------------------------------------------------------------+

By placing the entry ibmcam (for example) in /etc/modules (note that this
varies by distribution), you can have the module load at boot-time
automatically. You can then confirm the module was loaded by checking the
syslog or in the boot-time record with dmesg | less), where you should see an
entry such as the following:

+-------------------------------------------------------------------------------------------------+
|   Oct 18 12:43:12 K7 kernel: hub.c: new USB device 00:02.3-2, assigned address 3                |
|   Oct 18 12:43:12 K7 kernel: ibmcam.c: IBM PC Camera USB camera found (model 2, rev. 0x030a)    |
|   Oct 18 12:43:12 K7 kernel: usbvideo.c: ibmcam on /dev/video1: canvas=352x240 videosize=352x240|
+-------------------------------------------------------------------------------------------------+
-----------------------------------------------------------------------------

2.2.2. IEEE 1394 (Firewire??, i.Link??)

IEEE 1394 webcams require an IEEE 1394 PCI card or an IEEE 1394 bus port on
your mainboard. The IEEE interface has been supported in Linux since the
early 2.4-series kernel. If you are lucky enough to own such a device,
generic information on support of the IEEE 1394 bus in Linux can be found at
[http://www.linux1394.org] www.linux1394.org. If you have a kernel older than
2.4.2, you will need to patch your kernel with one of the patches found on
[http://download.sourceforge.net/linux1394] this page matched to your kernel
version. In addition, you will require [http://download.sourceforge.net/
libraw1394] libraw1394. The previously referenced linux1394.org site has a
great installation guide.

The IEEE1394 Digital Camera List, by Damien Douxchamps, offers an outstanding
summary of the capabilities of IEEE 1394 cameras as well as the current
status of support for individual models.
-----------------------------------------------------------------------------

2.2.3. Generic Parallel Port Support for Parport Webcams

For 2.2 and 2.4 kernel systems, parallel-port support must be enabled
statically or as a module (stock kernels usually have this enabled by
default). You may want to read more generic info about parallel-port device
support under the Linux kernel before starting this process. To find out for
sure if the module parport is loaded, you can check the dmesg file or use 
lsmod as outlined above. Using dmesg | less, you should see (among many other
lines) the following:

+------------------------------------------------------------------------------------+
|   Mar  3 08:00:25 K7 kernel: parport0: PC-style at 0x378 (0x778) [PCSPP,TRISTATE]  |
|   Mar  3 08:00:25 K7 kernel: parport0: irq 7 detected                              |
+------------------------------------------------------------------------------------+

If you are compiling your own kernel, enable 'Parallel Port support'. You
should enable 'IEEE 1284 transfer modes', and if you have x86 type
architecture, you should also enable 'PC-style hardware'.

If modprobe returns an error when you attempt to load the module, note that
you may need to determine and supply the hardware address when invoking 
modprobe. The most common address is 0x378 for an x86 system; 0x278 and 0x3BC
are other possibilities for integrated or ISA parallel ports. Add-in PCI
parallel ports may have unusual base addresses. You can also arrange multiple
devices with either the parport_pc or parport_arc modules, though that topic
is beyond the scope of this document.

Warning WARNING: Be sure you have the correct address before entering this   
        information at the command line or else your machine may become      
        unstable, crash or otherwise implode.                                

Your parallel port should be set to preferably "EPP" mode, or alternatively
ECP/EPP. "Bidirectional" (also known as "BPP" or "PS/2") may work, albeit
much more slowly. "Unidirectional" mode is unsuitable for scanning. The above
setting can usually be accessed through your BIOS menu, at least on x86
systems.
-----------------------------------------------------------------------------

2.3. Specific Webcam Models

Note that this information is frequently changing. The Linux-USB Device
Overview site is a great place to look if you have a USB webcam. Also, you
will want to check for your model's homepage at [http://www.exploits.org/v4l
/] http://www.exploits.org/v4l/. The information compiled below on specific
webcam models is from the same source, so you may find more up-to-date
information through the previous link. If you can't find an entry for your
particular hardware, you can find links to resources on how to write your own
driver!

Important It is important to note that if your camera isn't listed, the      
          easiest way to find out if your camera is supported is to find out 
          what chipset is used in its manufacture.                           

This information is usually present in the specifications published in your
webcam's manual or on the manufacturer's website.

If you can't find your camera model listed and aren't sure what chipset your
camera is made with, you should consider searching and/or subscribing to the
video4linux-list mailing list hosted by Redhat.
-----------------------------------------------------------------------------

2.3.1. 3com HomeConnect PC Digital Webcam

This driver is supported with the kernel patch located at the homeconnectusb
project web page. It may require a kernel recompile after patching depending
on your kernel version.
-----------------------------------------------------------------------------

2.3.2. CPiA based Webcams

Please see the project home page for up-to-date information. This chipset has
been used in the manufacture of both USB and parallel port webcams including
the following:

  * Aiptek HyperVcam Fun USB (non-OV511 based)
   
  * Creative Video Blaster WebCam II USB and parallel-port
   
  * CVideo-Mail Express parallel-port
   
  * Digicom Galileo USB and Digicom Galileo Plus
   
  * Dynalink Digital Camera
   
  * Ezonics EZCam (not Pro or Plus)
   
  * I-View NetView NV200M
   
  * Microtek EyeStar USB
   
  * Pace Color Video Camera USB
   
  * SuperCam WonderEye
   
  * TCE Netcam 310 USB
   
  * Terracam USB (non-OV511 based or Terracam Pro)
   
  * Trust SpaceC@m Lite USB and SpaceC@m 100
   
  * Utopia USB Camera
   
  * ZoomCam USB and parallel-port
   

-----------------------------------------------------------------------------
2.3.3. SE401, SE402 and EP800 based USB webcams

This project is a work in progress. The drivers and other useful information
are available at the project homepage located [http://
members.brabant.chello.nl/~j.vreeken/se401] here. As of writing this, it is
necessary to patch and recompile your kernel in order to obtain support for
these models. The driver supports the following:

SE401 chipset via the 'se401' driver:

  * Aox SE401 camera
   
  * Philips PCVC665 USB VGA webcam 'Vesta Fun'
   
  * Kensington VideoCAM PC Camera (Models 67014-67017)
   

SE402 and EP 800 chipsets via the 'epcam' driver

  * Spypen Actor
   
  * Rimax Slim Multicam
   
  * Concord Eye-Q Easy
   
  * Creative PD1001
   
  * Chicony DC-100
   
  * Endpoints SE402 and EP800
   

-----------------------------------------------------------------------------
2.3.4. OmniVision based Webcams

This category includes a multitude of webcam and video-capture devices
manufactured by Omnivision, including the OV511(+), OV518(+), OV6620, OV6630,
OV7610, and OV7620AE. The project homepage is [http://alpha.dyndns.org/ov511]
here. Supported models include:

  * Aiptek HyperVcam Home and Mobile
   
  * Amitech AWK-300
   
  * I-view NetView NV300M
   
  * TEVion MD9308
   
  * Intel Me2Cam
   
  * Dlink DSB C100, C300
   
  * Hawking Tech. UC-110, UC-300 and UC-310
   
  * Puretek PT-6007
   
  * Alpha Vision Tech AlphaCam SE model AC-520
   
  * Creative Labs WebCam model PD1001 with OV518 chipset
   
  * Creative Labs WebCam 3, WebCam Go, Webcam Go Plus
   
  * Elecom UCAM-C1C20
   
  * Elta WEBCam 8211 PCC
   
  * Ezonics EZPhone Cam
   
  * Philips ToUCam XS (old version with OV518)
   
  * LG Electronics LPC-UM10
   
  * Lifeview various USB Life TV models
   
  * Genius VideoCam Express
   
  * AverMedia Intercam Elite
   
  * Maxxtro Cam22U
   
  * MediaForte MV300, PC Vision 300
   
  * Terratec TerraCam PRO and some TerraCam models
   
  * OmniVision (except those with OV519)
   
  * TRENDNet TV-PC301
   
  * Trust Sp@ceC@m USB
   
  * Lifetec LT9388
   
  * BestBuy EasyCam U
   
  * Maxell Maxcam
   
  * TCE NetCam 310u
   
  * Medion MD9388
   
  * Webeye 2000B
   
  * Suma eON
   
  * Prochips PCA-3100
   
  * Ezonics EZ USB Cam II (the OV511+ models)
   
  * Waytech I-Pac VIC-30
   
  * Zoom Telephonics ZoomCam III USB (model 1598)
   

-----------------------------------------------------------------------------
2.3.5. Logitech (formerly Connectix) Quickcam Support

The QuickCam VC USB and parallel port model webcams are supported by the
driver offered [ http://digilander.libero.it/demarchidaniele/qcamvc/
quickcam-vc.html] here. A kernel patch and recompile are necessary for
support of this model.

The Quickcam driver is represented by two different projects that offer two
different flavors of driver for certain Quickcam models, both of which are
stand-alone drivers that do not require a kernel patch or recompile. The
[http://qce-ga.sourceforge.net/] qce-ga and [http://www.ee.oulu.fi/~tuukkat/
quickcam/quickcam.html] qc-usb drivers support the following models:

  * Logitech (earlier models of) Quickcam Express
   
  * Quickcam Web
   
  * Legocam
   
  * Dexxa Webcam
   
  * Labtec Webcam
   

 

The qc-usb driver is more experimental but reportedly works better on some
models such as the Quickcam Web. Also, I have recieved correspondence that
newer versions of the Logitech Quickcam Express no longer work with the above
drivers; instead [http://home.tiscali.dk/tomasgc/labtec/] this page offers an
experimental driver that claims to support the newer model.

Note to Redhat users: The qce-ga driver doesn't compile properly using the
modified kernel source provided in Redhat 9, but a fix is available [http://
www.ee.oulu.fi/~tuukkat/quickcam/FAQ] here.

Some Logitech camera models are supported by the Philips driver in Section
2.3.8.
-----------------------------------------------------------------------------

2.3.6. ICM532 Based Webcams

One driver for this chipset, [http://icm532.sourceforge.net/home.html]
homepage here, is now merged into the 2.6 kernel source; the other is (per
the developer's own description) experimental and available [http://
home.tiscali.dk/tomasgc/labtec/] here. Either or both claim to support the
following models:

  * IC-Media Corp Pencam
   
  * Newer versions of the Logitech Quickcam Express
   
  * Newer versions of the Labtec Webcam
   
  * Biolux 654 microscope
   
  * Ezonics EZCam USB II (uvt8532)
   
  * Ezonics EZCam USB III
   
  * TerraCam USB
   
  * Stick Webcam
   
  * Mini WebCam
   
  * Tucan PenCam
   
  * Che-ez! Webbie
   
  * SNAKE EYE SI-8480/8481
   
  * PC CAM CP03
   
  * WEB Camera PBC0006
   
  * Clipcam
   

-----------------------------------------------------------------------------
2.3.7. NW802 Based Webcams

This chipset, manufactured by DIVIO, is supported by the driver found [http:/
/nw802.sourceforge.net] here. The models supported include the following:

  * BTC SurfCam CMOS300k
   
  * Mustek WCam 300
   
  * Logitech QuickCam Pro USB (the earlier "dark focus ring" model)
   

-----------------------------------------------------------------------------
2.3.8. Philips USB Webcams

Because of the expiration of the Non-Disclosure-Agreement between Philips
Corporation and the former maintainer of the pwc driver, the previous kernel
support for Philips PWC-chip-based webcams has been removed. Luckily a new,
still experimental driver that does not require a proprietary module is under
development. The old site, with a discussion of the change, can be seen at
[http://www.smcc.demon.nl/webcam/] http://www.smcc.demon.nl/webcam/; the new
driver is maintained at [http://www.saillard.org/linux/pwc/] saillard.org
with more information at the [] PWC Documentation Project. 

Philips models supported by the above include the following.

  * PCA645VC
   
  * PCA646VC
   
  * PCVC675K Vesta, Vesta Pro and Vesta Scan
   
  * PCVC720K/40 ToUCam XS, ToUCam Fun, ToUCam Pro and ToUCam Scan
   
  * Askey VC010
   
  * Creative Labs Webcam 5, Pro Ex
   
  * Logitech 3000 and 4000 Pro, Notebook Pro, and Zoom
   
  * Samsung MPC-C10 and MPC-C30
   
  * Sotec Afina Eye
   
  * Visionite VCS UM100 and UC300
   

-----------------------------------------------------------------------------
2.3.9. SPCA50X USB Camera Linux Driver

Information regarding this chipset can be found [http://
spca50x.sourceforge.net/spca50x.php] here, and is under heavy development and
includes partial or complete support for the following models:

  * Kodak DVC-325 and EZ200
   
  * Creative PC-CAM 300, 600, 750
   
  * Genius VideoCAM Express V2
   
  * Micro Innovation IC 200/IC 150
   
  * Logitech ClickSmart 310, 420, 510, 820 and Cordless models
   
  * Logitech Pocket750
   
  * Benq DC 1016, 1300, 1500, 3410
   
  * Flexcam 100
   
  * Aiptek MegaCam, [1.3 Megapixel] Mini PenCam and PocketCam 1.3M Smart
   
  * Finet Technology Palmpix DC-85
   
  * Pure DigitalDakota
   
  * 3Com Home Connect lite
   
  * Megapix V4
   
  * Mustek gSmart: Mini, Mini2, Mini3, LCD 2, LCD 3
   
  * Digital Dream Enigma 1.3, Epsilon 1.3
   
  * Maxwell Compact Pc PM3
   
  * Jenoptik models
   
  * Minton S-Cam F5
   
  * D-Link DSC-350
   
  * Trust FamilyC@m 300 Movie
   
  * Aiptek Pocket DV, PocketDVII, DV3100+, mini PenCam 2, PocketCam 3M,
    Pencam SD 2, Pocket DV3500
   
  * Hama Sightcam 100
   
  * Micro Innovations IC50C, IC400c
   
  * FlyCam USB100
   
  * Arowana USB Camera 300 K
   
  * Intel Easy PC Camera, CS120 (Easy PC Share), PC Camera Pro (CS431),
    Pocket PC Camera (CS630)
   
  * Grandtec V.cap
   
  * Sigma-Apo Petcam
   

-----------------------------------------------------------------------------
2.3.10. STV0680 based Models

The USB version of webcams made with this chipset are supported by the 2.4.18
and above kernel with the stv680.o module. Alternatively, you can obtain the
source from [http://stv0680-usb.sourceforge.net] the project homepage. This
driver supports models including the Aiptek Pencam and the Nisis Quickpix 2.

If you have a serial version, the main one of which is the Scan e-Studio, you
should go [http://stv0680.sourceforge.net] here.
-----------------------------------------------------------------------------

2.3.11. Winbond w9966cf

This is a driver for the parallel-port interface that supports the Philips
SAA7111 CCD-control chip as found on the Lifeview Flycam SUPRA webcam. It is
included in the late 2.4 kernel series and later under the heading
'video4linux' support. The homepage for this project is [http://
hem.fyristorg.com/mogul/w9966.html] here. 
-----------------------------------------------------------------------------

2.3.12. Xirlink C-it?? HDCS-1000 based Webcams

This driver is for the USB webcams manufactured by Xirlink, IBM (PC Camera)
and Veo Stingray model webcams. Support has been in the Linux kernel USB
section since 2.2.12. The homepage is at [http://www.linux-usb.org/ibmcam]
http://www.linux-usb.org/ibmcam.
-----------------------------------------------------------------------------

3. Accessing the Video Device

The following section applies to all connection types.
-----------------------------------------------------------------------------

3.1. The Video Devices Node

The Linux kernel requires a virtual device node be created to access and
control the device in question. It may have already been created for you at
boot-up; ls -l /dev/video* (with an asterisk) or alternatively find /dev
-name video* or even visual inspection of the /dev directory with your
favorite file manager can give you an idea if the video devices exist. If so
you can proceed to Section 3.2; if not you will need to create them manually.

An easy way to create them, if available with your Linux distribution, is use
of the MAKEDEV script, which may be located in /dev or the usual places for
storing executable commands (/bin,/sbin and so on). The manual page for
MAKEDEV (man MAKEDEV) can guide you further, but be aware of the
device-specific command options. If MAKEDEV doesn't work or doesn't exist, or
you just prefer doing things the hard way, move on to the next paragraph.

A device can be created as a block (such as a drive), a fifo
(file-in-file-out or pipe, as in xconsole) or a character device, which
represents other hardware. Each device has a major and a minor number 
"coordinate" to tell the kernel what it is and where to access it. These
numbers are not arbitrary. The major number 81 with minor number 0, 1, 2, and
so on are by convention assigned to Video4linux devices, including TV tuner
boards and webcams. In order to create the video device /dev/video0, use 
mknod at the command line:

+---------------------------------------------------------------------------+
|   #  mknod /dev/video0 c 81 0                                             |
+---------------------------------------------------------------------------+

where c represents a character device.

 You can use the following script, which I have borrowed from the kernel
source (located in linux/Documentation/video4linux/bttv/MAKEDEV of the source
tree):

+---------------------------------------------------------------------------+
|   #!/bin/bash                                                             |
|   function makedev () {                                                   |
|        for dev in 0 1 2 3; do echo "/dev/$1$dev:                          |
|        char 81 $[ $2 + $dev ]" rm -f /dev/$1$dev                          |
|        mknod /dev/$1$dev c 81 $[ $2 + $dev ] chmod                        |
|        666 /dev/$1$dev                                                    |
|        done                                                               |
|                                                                           |
|        # symlink for default device                                       |
|        rm -f /dev/$1 ln -s /dev/${1}0 /dev/$1                             |
|        }                                                                  |
|                                                                           |
|        # see http://roadrunner.swansea.uk.linux.org/v4lapi.shtml          |
|        echo "*** new device names ***" makedev video                      |
|        0 makedev radio 64 makedev vtx 192 makedev vbi 224                 |
|        # "*** old device names (for compatibility only) ***"              |
|        #makedev bttv 0 #makedev bttv-fm 64 #makedev bttv-vbi 224          |
+---------------------------------------------------------------------------+

Simply copy and paste the above into your favorite editing program, save it
as MAKEDEV or whatever name you like, make it executable (i.e., chmod u+x
MAKEDEV), and then execute it as root:

 
+---------------------------------------------------------------------------+
|   #  ./MAKEDEV                                                            |
+---------------------------------------------------------------------------+
-----------------------------------------------------------------------------

3.2. Groups and Permissions

It is a good idea to be sure that your user account can access the device
once all modules are loaded and device nodes created. The most
security-conscious way to do that is to add access for a particular group. On
my system, the members of the group 'video' are allowed to use the webcam,
scanner and other photographic devices. The way to accomplish this is to
first change the ownership of the devices in /dev like so (as root):

+---------------------------------------------------------------------------+
|   #  chown root.video /dev/usb/video*                                     |
+---------------------------------------------------------------------------+

...where root.video are the owner and group the device will now belong to.
Obviously, the specific command will vary by your system and the type of
device. It is important that you change the ownership of the device node
itself and not the symlink; symlinks' ownerships are affected only by
changing the parent devices or files they point to.

To see if your user account is a member of the group in question, as root
issue the following command: grep -e video /etc/group. You should see
something like the following:

+---------------------------------------------------------------------------+
|   video:x:44:                                                             |
+---------------------------------------------------------------------------+

...where '44' is the group number. Since no members follow the last colon in
the 'video' group, we can add them, let's say user 'jhs' with the command

+---------------------------------------------------------------------------+
|   #  adduser jhs  video                                                   |
+---------------------------------------------------------------------------+

After this, it's simply a matter of allowing read and write access for the
user in question of the device like so:

+---------------------------------------------------------------------------+
|   #  chmod g+rw /dev/v4l/video0                                           |
+---------------------------------------------------------------------------+

...where g+rw means add read and write access for group. See the
documentation for chmod (man chmod or info chmod) for further info.
-----------------------------------------------------------------------------

4. Framegrabbing Applications

-----------------------------------------------------------------------------
4.1. Command Line Programs

As implied by the title these do not require the X Window System to operate
your camera and capture images.
-----------------------------------------------------------------------------

4.1.1. Streamer

Streamer is a versatile program that allows a capture from a webcam or video
device using only the command line. It may be offered in your Linux
distribution's Xawtv package, or may need to be fetched separately as in
Debian. You can find it and more information at [http://www.bytesex.org/
xawtv] Gerd Knorr's Xawtv homepage.

To take a standard JPEG picture from the command line where the camera is
accessed through /dev/video0:

+---------------------------------------------------------------------------+
|   $  streamer -c /dev/video0 -b 16 -o outfile.jpeg                        |
+---------------------------------------------------------------------------+

...where -b is the number of colors (in bpp, whether 15, 16, 24 or 32) and -o
is the output filename that will be dropped into the current directory
(specify -o /path/outfile.jpg to place it elsewhere). If you are going to
capture multiple images be sure to append the output file name with zeros, as
streamer can name the capture files in sequence, i.e., -o outfile000.jpeg
becomes outfile001.jpeg, outfile002.jpeg, and so on.

To make an .avi file:

+-----------------------------------------------------------------------------------+
|   $  streamer -q -c /dev/video0 -f rgb24 -r 3 -t 00:30:00 -o /home/jhs/outfile.avi|
+-----------------------------------------------------------------------------------+

...where -q is for 'quiet' execution (no message output), -f is 'format'
(rgb24 is TrueColor avi), -r is the frames per second and -t is the time of
recording (30 minutes). Streamer can capture raw and Quicktime??
(non-Sorensen) formats and can capture audio as well. See streamer --help for
more information.
-----------------------------------------------------------------------------

4.1.2. camE

CamE is a command-line program that works in daemon mode to capture frames
from your v4l device for archive or upload (to a webserver, for example) via
ftp or scp. You can overlay other graphics, timestamp the frames, or add
other dynamic text all by altering the appropriate line in the configuration
file. See [http://linuxbrit.co.uk/camE/] the camE homepage for more
information.
-----------------------------------------------------------------------------

4.1.3. Motion

Motion is a brilliant program that is able to monitor the video signal from
one or several webcams. It can record periodic snapshots, and when motion is
detected, record an mpeg and/or perform another action such as sending an
email or executing a command. It can track and graphically mark the motion it
detects, feed files via an http server to your website, stream them to
another application and more. The number of command line options may be
intimidating; there is however, a Wiki available online that outlines the
various command and configuration file options nicely. The motion homepage
can be found [http://www.lavrsen.dk/twiki/bin/view/Motion/WebHome] here.
-----------------------------------------------------------------------------

4.1.4. Webcam

Webcam is an automated command line tool for operating a webcam that is also
available from [http://www.bytesex.org/xawtv] the Xawtv homepage. It is
excellent for automated operation such as from a cron job, as it requires no
command line options, only a previously edited configuration file (usually ~
/.webcamrc). It is similar to camE above in that one can captures images and
upload them to a Web-Server via ftp or ssh.
-----------------------------------------------------------------------------

4.1.5. SANE

SANE, or Scanner Access Now Easy, supports access of v4l devices including
webcams in later versions. If you are familiar with using a photographic
scanner device in Linux, you may be interested in using SANE for image
capture, especially since a few devices double as both scanners and digital
cameras. See the relevant sections of the Scanner-HOWTO [http://tldp.org/
HOWTO/Scanner-HOWTO/sane.html#getting-SANE] here.
-----------------------------------------------------------------------------

4.2. GUI(Grapical User Interface)-Based Programs

4.2.1. Xawtv

Xawtv is an X-based program for accessing video devices in Linux including TV
tuning devices and webcams. The home page is at [http://bytesex.org/xawtv]
http://bytesex.org/xawtv. 

When you first try out your webcam, and you think things are configured
right, use the -hwscan option:

+------------------------------------------------------------------------------------------------------------------------------------------+
|   $  xawtv -hwscan This is xawtv-3.72, running on Linux/i686 (2.4.21) looking for available devices                                      |
|                                                                                                                                          |
|   /dev/v4l/video0: OK          [ -device /dev/v4l/video0 ] type : v4l name : BT878(Hauppauge (bt878)) flags: overlay capture tuner       |
|   /dev/v4l/video1: OK          [ -device /dev/v4l/video1 ] type : v4l name : IBM USB Camera           flags: capture                     |
+------------------------------------------------------------------------------------------------------------------------------------------+

...so now you can see the available devices (your output may differ
substantially). Try opening an xterm and running xawtv, grabbing from your
webcam video device:

+-----------------------------------------------------------------------------+
|   $  xawtv -c /dev/video1 This is xawtv-3.72, running on Linux/i686 (2.4.21)|
+-----------------------------------------------------------------------------+

...and (hopefully) your camera will begin capturing to a window on your
desktop. You may see some error messages in your xterm if things don't work
that can be helpful to diagnose configuration problems. If you aren't
interested in all that, and things work for you, launch from your window
manager's menu next time. You can read about more xawtv options with man
xawtv.
-----------------------------------------------------------------------------

4.2.2. Gqcam

[http://cse.unl.edu/~cluening/gqcam/] Gqcam is a graphical GTK+-based
application originally written to access Connectix QuickCams but now supports
nearly all Video4Linux compatible webcam devices. It has an intuitive
interface that makes viewing, taking snapshots, and configuring webcam
settings blissfully easy. It is highly recommended for those who only want to
take a picture here and there without editing a configuration file or using
the command line.
-----------------------------------------------------------------------------

4.2.3. Camorama

Camorama is a graphical GTK+2.0-based application very similar to gqcam
written for the Gnome2 desktop. The home page is [http://
camorama.fixedgear.org/] here.
-----------------------------------------------------------------------------

4.2.4. GnomeMeeting

GnomeMeeting is a VOIP/IP-Telephony application for the Gnome2 desktop that
also supports videoconferencing with a webcam. The homepage can be found at
[http://www.gnomemeeting.org/] gnomemeeting.org.
-----------------------------------------------------------------------------

5. Troubleshooting

5.1. Help, I have a USB webcam and don't know exactly what model it is and/or
who the manufacturer is. What do I do?

Use lsusb; it can give you an idea of what other USB devices are available on
your system, too:

+-----------------------------------------------------------------------------------------+
|   $  lsusb                                                                              |
|   Bus 007 Device 001: ID 0000:0000                                                      |
|   Bus 006 Device 001: ID 0000:0000                                                      |
|   Bus 005 Device 001: ID 0000:0000                                                      |
|   Bus 004 Device 001: ID 0000:0000                                                      |
|   Bus 003 Device 003: ID 0545:8080 Xirlink, Inc. IBM C-It WebCam                        |
|   Bus 003 Device 002: ID 046d:0840 Logitech, Inc. QuickCam Express                      |
|   Bus 003 Device 001: ID 0000:0000                                                      |
|   Bus 002 Device 003: ID 051d:0002 American Power Conversion Back-UPS Pro 500/1000/1500 |
|   Bus 002 Device 001: ID 0000:0000                                                      |
|   Bus 001 Device 001: ID 0000:0000                                                      |
+-----------------------------------------------------------------------------------------+

The numbers after 'ID' are the Vendor and Product numbers, respectively. They
can then be looked up in [http://www.linux-usb.org/usb.ids] the Linux USB ID
catalog.

If lsusb is not available to you, and you have support for /proc filesystem
support and USB-filesystem support, issue the following at the command line:

+---------------------------------------------------------------------------+
|   $  cat /proc/bus/usb/devices                                            |
+---------------------------------------------------------------------------+

You should receive output including (but not necessarily limited to) the
following:

+---------------------------------------------------------------------------+
|   T:  Bus=01 Lev=01 Prnt=01 Port=01 Cnt=01 Dev#=3 Spd=12 MxCh=0           |
|   D:  Ver= 1.01 Cls=ff(vend.) Sub=ff Prot=ff MxPS=8 #Cfgs=1               |
|   P:  Vendor=0545 ProdID=8080 Rev= 3.0a                                   |
|   S:  Product=USB IMAGING DEVICE                                          |
+---------------------------------------------------------------------------+

The line beginning "T:" is the USB bus the device is attached to. The "P:"
indicates (obviously) the vendor and product ID, which are catalogued at the 
linux USB Project homepage.
-----------------------------------------------------------------------------

5.2. Help, I can't find the camera device in /dev!

Assuming your connection type is supported, and your camera is working, see 
Section 3.1.
-----------------------------------------------------------------------------

5.3. Help, I can see the camera device (both in person and as a device node
in /dev), but I can't access it!

See Section 3.2.
-----------------------------------------------------------------------------

5.4. Help, my camera has a driver that is source-only, i.e., has to be built
by me! Where do I start?

First, check if your Linux distribution offers a pre-compiled binary of the
driver. You can then load it as you normally would for a module. If that is
not the case, be sure you have kernel sources installed. You will also need
at a minimum GNU make, gcc, binutils and perhaps other programs installed
depending on your distribution. (Debian users should see the next section for
instructions specific to that distribution.)

Download the driver source (in this example named src.tar.gz) and uncompress/
untar it:

+---------------------------------------------------------------------------+
|   $  tar -xvzf src.tar.gz                                                 |
+---------------------------------------------------------------------------+

Then, change to the directory of your kernel source:

+---------------------------------------------------------------------------+
|   #  cd /usr/src/linux                                                    |
+---------------------------------------------------------------------------+

Make the necessary source files:

+---------------------------------------------------------------------------+
|   #  make oldconfig # make dep                                            |
+---------------------------------------------------------------------------+

Now, change to the directory where you unpacked the driver source and read
the README and/or INSTALL files for instructions on how to make the driver.
Usually this involves some combination of "make" "make all" and/or "make
install." Assuming it compiles correctly, you can simply load the new module
with modprobe. If you have any problems, see Section 5.7.

-----------------------------------------------------------------------------
5.5. I am using Debian GNU/Linux. Is there an easier way to go through all
this kernel compiling stuff and building of source modules?

It is far simpler, in your author's humble opinion, to use the automated
kernel-package utility. First, install it and the dependencies using apt-get.
Next, install the kernel source that you want (e.g., apt-get install
kernel-source-2.X.X). Untar the bzip2'd kernel source with tar -xvjf and then
make a symbolic link called linux that points to the new source: 

+---------------------------------------------------------------------------+
|   #  ln -s /usr/src/kernel-source-2.X.X /usr/src/linux                    |
|                                                                           |
+---------------------------------------------------------------------------+

Then cd /usr/src/linux and clean: make-kpkg clean, followed by make
menuconfig or make xconfig as you would if compiling a new kernel. Next, you
can use make-kpkg kernel_image and then install your new kernel package that
has been deposited in /usr/src with dpkg -i ../kernel-image-2.X.X. Next, you
can get the pre-packaged source driver using apt. So, in the case of the
Quickcam Express, the package is qc-usb-source:

+---------------------------------------------------------------------------+
|   #  apt-get install qc-usb-source                                        |
+---------------------------------------------------------------------------+

...and untar the archive:

+---------------------------------------------------------------------------+
|   #  tar -xvzf qc-usb-modules.tar.gz                                      |
+---------------------------------------------------------------------------+

This will uncompress the source into the /usr/src/modules directory. The
final step, while still in /usr/src/linux is to make the modules with
kernel-package:

+---------------------------------------------------------------------------+
|   #  make-kpkg modules_image                                              |
+---------------------------------------------------------------------------+

Install the new package, in /usr/src/, called qc-usb-modules-[arch].deb using
dpkg -i. Finally, load the module:

+---------------------------------------------------------------------------+
|   #  modprobe quickcam                                                    |
+---------------------------------------------------------------------------+

Check the documentation in /usr/share/doc/kernel-package for any problems.
-----------------------------------------------------------------------------

5.6. Help, my camera is supported by a driver that has to be patched into my
kernel! What do I do?

 See the section on patching of the Kernel-HOWTO at [http://tldp.org] The
Linux Documentation Project.

The short and unguaranteed version of patching, by your humble author, goes
as follows: Be sure you have the same prerequisites outlined in Section 5.4
installed. First, on the command line or in an xterm change to the source
directory of the kernel version you are (or will be) running with the camera
patch (in this example named patch.diff).

+---------------------------------------------------------------------------+
|   #  cd /usr/src/linux                                                    |
|   #  patch -p1 -E patch.diff                                              |
+---------------------------------------------------------------------------+

You should see a confirmation that the 'hunks' were successfully applied. At
this point, you can make menuconfig or whatever program you use to recompile,
enabling the appropriate support. If any of the hunks failed, or you run into
any problems in addition to the link referenced above you, should consult man
patch and Section 5.7.
-----------------------------------------------------------------------------

5.7. Help--as in, where can I get more of it?

See the video4linux mailing list headquarters at [https://listman.redhat.com/
mailman/listinfo/video4linux-list] https://listman.redhat.com/mailman/
listinfo/video4linux-list.
-----------------------------------------------------------------------------

5.8. Help, I want to contribute to Video4Linux support in Linux! Who do I get
in touch with?

See [http://www.thedirks.org/v4l2/peopleprojects.htm] this page.
-----------------------------------------------------------------------------

A. Gnu Free Documentation License

Version 1.2, November 2002

Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 59 Temple Place,
Suite 330, Boston, MA 02111-1307 USA Everyone is permitted to copy and
distribute verbatim copies of this license document but changing it is not
allowed.

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You may copy and distribute the Document in any medium, either commercially
or noncommercially, provided that this License, the copyright notices, and
the license notice saying this License applies to the Document are reproduced
in all copies, and that you add no other conditions whatsoever to those of
this License. You may not use technical measures to obstruct or control the
reading or further copying of the copies you make or distribute. However, you
may accept compensation in exchange for copies. If you distribute a large
enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may
publicly display copies.

3. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have printed
covers) of the Document, numbering more than 100, and the Document's license
notice requires Cover Texts, you must enclose the copies in covers that
carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the
front cover, and Back-Cover Texts on the back cover. Both covers must also
clearly and legibly identify you as the publisher of these copies. The front
cover must present the full title with all words of the title equally
prominent and visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve the
title of the Document and satisfy these conditions, can be treated as
verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you
should put the first ones listed (as many as fit reasonably) on the actual
cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more
than 100, you must either include a machine-readable Transparent copy along
with each Opaque copy, or state in or with each Opaque copy a
computer-network location from which the general network-using public has
access to download using public-standard network protocols a complete
Transparent copy of the Document, free of added material. If you use the
latter option, you must take reasonably prudent steps, when you begin
distribution of Opaque copies in quantity, to ensure that this Transparent
copy will remain thus accessible at the stated location until at least one
year after the last time you distribute an Opaque copy (directly or through
your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give them
a chance to provide you with an updated version of the Document.

4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the
conditions of sections 2 and 3 above, provided that you release the Modified
Version under precisely this License, with the Modified Version filling the
role of the Document, thus licensing distribution and modification of the
Modified Version to whoever possesses a copy of it. In addition, you must do
these things in the Modified Version:

A. Use in the Title Page (and on the covers, if any) a title distinct from
that of the Document, and from those of previous versions (which should, if
there were any, be listed in the History section of the Document). You may
use the same title as a previous version if the original publisher of that
version gives permission.

B. List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified Version,
together with at least five of the principal authors of the Document (all of
its principal authors, if it has fewer than five), unless they release you
from this requirement.

C. State on the Title page the name of the publisher of the Modified Version,
as the publisher.

D. Preserve all the copyright notices of the Document.

E. Add an appropriate copyright notice for your modifications adjacent to the
other copyright notices.

F. Include, immediately after the copyright notices, a license notice giving
the public permission to use the Modified Version under the terms of this
License, in the form shown in the Addendum below.

G. Preserve in that license notice the full lists of Invariant Sections and
required Cover Texts given in the Document's license notice.

H. Include an unaltered copy of this License.

I. Preserve the section Entitled "History", Preserve its Title, and add to it
an item stating at least the title, year, new authors, and publisher of the
Modified Version as given on the Title Page. If there is no section Entitled
"History" in the Document, create one stating the title, year, authors, and
publisher of the Document as given on its Title Page, then add an item
describing the Modified Version as stated in the previous sentence.

J. Preserve the network location, if any, given in the Document for public
access to a Transparent copy of the Document and likewise the network
locations given in the Document for previous versions it was based on. These
may be placed in the "History" section. You may omit a network location for a
work that was published at least four years before the Document itself, or if
the original publisher of the version it refers to gives permission.

K. For any section Entitled "Acknowledgements" or "Dedications", Preserve the
Title of the section, and preserve in the section all the substance and tone
of each of the contributor acknowledgements and/or dedications given therein.

L. Preserve all the Invariant Sections of the Document, unaltered in their
text and in their titles. Section numbers or the equivalent are not
considered part of the section titles.

M. Delete any section Entitled "Endorsements". Such a section may not be
included in the Modified Version.

N. Do not retitle any existing section to be Entitled "Endorsements" or to
conflict in title with any Invariant Section.

O. Preserve any Warranty Disclaimers. If the Modified Version includes new
front-matter sections or appendices that qualify as Secondary Sections and
contain no material copied from the Document, you may at your option
designate some or all of these sections as invariant. To do this, add their
titles to the list of Invariant Sections in the Modified Version's license
notice. These titles must be distinct from any other section titles. You may
add a section Entitled "Endorsements", provided it contains nothing but
endorsements of your Modified Version by various parties--for example,
statements of peer review or that the text has been approved by an
organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list of
Cover Texts in the Modified Version. Only one passage of Front-Cover Text and
one of Back-Cover Text may be added by (or through arrangements made by) any
one entity. If the Document already includes a cover text for the same cover,
previously added by you or by arrangement made by the same entity you are
acting on behalf of, you may not add another; but you may replace the old
one, on explicit permission from the previous publisher that added the old
one.

The author(s) and publisher(s) of the Document do not by this License give
permission to use their names for publicity for or to assert or imply
endorsement of any Modified Version.

5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified versions,
provided that you include in the combination all of the Invariant Sections of
all of the original documents, unmodified, and list them all as Invariant
Sections of your combined work in its license notice, and that you preserve
all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple
identical Invariant Sections may be replaced with a single copy. If there are
multiple Invariant Sections with the same name but different contents, make
the title of each such section unique by adding at the end of it, in
parentheses, the name of the original author or publisher of that section if
known, or else a unique number. Make the same adjustment to the section
titles in the list of Invariant Sections in the license notice of the
combined work.

In the combination, you must combine any sections Entitled "History" in the
various original documents, forming one section Entitled "History"; likewise
combine any sections Entitled "Acknowledgements", and any sections Entitled
"Dedications". You must delete all sections Entitled "Endorsements".

6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in the
collection, provided that you follow the rules of this License for verbatim
copying of each of the documents in all other respects.

You may extract a single document from such a collection and distribute it
individually under this License, provided you insert a copy of this License
into the extracted document and follow this License in all other respects
regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate and
independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright resulting from
the compilation is not used to limit the legal rights of the compilation's
users beyond what the individual works permit. When the Document is included
in an aggregate, this License does not apply to the other works in the
aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of
the Document, then if the Document is less than one half of the entire
aggregate, the Document's Cover Texts may be placed on covers that bracket
the Document within the aggregate, or the electronic equivalent of covers if
the Document is in electronic form. Otherwise, they must appear on printed
covers that bracket the whole aggregate.

8. TRANSLATION

Translation is considered a kind of modification, so you may distribute
translations of the Document under the terms of section 4. Replacing
Invariant Sections with translations requires special permission from their
copyright holders, but you may include translations of some or all Invariant
Sections in addition to the original versions of these Invariant Sections.
You may include a translation of this License, and all the license notices in
the Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions of
those notices and disclaimers. In case of a disagreement between the
translation and the original version of this License or a notice or
disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications",
or "History", the requirement (section 4) to Preserve its Title (section 1)
will typically require changing the actual title.

9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except as
expressly provided for under this License. Any other attempt to copy, modify,
sublicense, or distribute the Document is void and will automatically
terminate your rights under this License. However, parties who have received
copies, or rights, from you under this License will not have their licenses
terminated so long as such parties remain in full compliance.

10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU
Free Documentation License from time to time. Such new versions will be
similar in spirit to the present version but may differ in detail to address
new problems or concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the
Document specifies that a particular numbered version of this License "or any
later version" applies to it, you have the option of following the terms and
conditions either of that specified version or of any later version that has
been published (not as a draft) by the Free Software Foundation. If the
Document does not specify a version number of this License, you may choose
any version ever published (not as a draft) by the Free Software Foundation.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the
License in the document and put the following copyright and license notices
just after the title page:

Copyright (c) YEAR YOUR NAME. Permission is granted to copy, distribute, and/
or modify this document under the terms of the GNU Free Documentation
License, Version 1.2 or any later version published by the Free Software
Foundation; with no Invariant Sections, no Front-Cover Texts, and no
Back-Cover Texts. A copy of the license is included in the section entitled
"GNU Free Documentation License".

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this: with the Invariant Sections being
LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the
Back-Cover Texts being LIST. If you have Invariant Sections without Cover
Texts, or some other combination of the three, merge those two alternatives
to suit the situation.

If your document contains nontrivial examples of program code, we recommend
releasing these examples in parallel under your choice of free software
license, such as the GNU General Public License, to permit their use in free
software.
