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.

dmesg | less
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

find /lib/modules -name ibmcam.o

ls -R /lib/modules/`uname -r`/kernel

./usb: usbvideo.o usbcore.o ibmcam.o

lsmod

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

modprobe -v ibmcam

2.2. Supporting the Connection Type

   $  cat /proc/filesystems

   nodev    usbdevfs 
   nodev    usbfs

   #  lsmod

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

   #  modprobe -v ibmcam

   Using /lib/modules/2.4.20/kernel/drivers/usb/ibmcam.o

   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

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/. 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!

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.

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.

4.1. Command Line Programs

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

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

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

4.2. GUI(Grapical User Interface)-Based Programs

   $  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

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

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 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 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.

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