How can I assign a webcam to a specific /dev/video#?

windisch · 09-12-2008, 11:28 AM

Here's the situation. I have a MythTV box with 2 pci capture devices and a usb web cam I plug in every now and then. The problem happens if I leave the webcam plugged in and reboot. It assigns the webcam as /dev/video0 and the 2 capture cards as 1 and 2, which messes up MythTV. Is there a way to set the assignment of the USB device to say 3 or 4 so it won't mix up my devices if I have it plugged in or not?

Thanks,
Adam

tredegar · 09-12-2008, 11:45 AM

This is what udev is for.
You need to write a udev rule for your webcam to make it always be assigned to /dev/webcam for example.
See here: http://www.reactivated.net/writing_udev_rules.html

windisch · 09-24-2008, 06:46 AM

Thanks tredegar. That got me on the right track. I'm testing out a udev rule right now. I appreciate your help.

tredegar · 09-24-2008, 09:42 AM

Quote:

I'm testing out a udev rule right now

Excellent! I hope you are making progress.

Please post your solution (when you have it) as I am sure other people will be interested to read how you went about writing your rule, deciding where to put it, and how you tested it.

You could even send Daniel Drake (who wrote "Writing udev rules") a link to your post here in case he'd like to include it in his list of examples.

windisch · 09-25-2008, 01:23 PM

I'll try to do my best.

The pages that helped me figure this out were:

http://liquidat.wordpress.com/2008/0...or-udev-rules/
and
http://ubuntuforums.org/showthread.php?p=5698771

In my situation I did an lsusb and got this output:

Code:

Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 003: ID 046d:08b2 Logitech, Inc. QuickCam Pro 4000
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 004: ID 03f0:020c Hewlett-Packard Multimedia Keyboard
Bus 002 Device 003: ID 03f0:010c Hewlett-Packard Multimedia Keyboard Hub
Bus 002 Device 002: ID 045e:0039 Microsoft Corp. IntelliMouse Optical
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub

Now that I found my ID for my Logitech Webcam, I created a udev rule at

Code:

/etc/udev/rules.d/25-name-video-devices.rules

Which contained:

Code:

SUBSYSTEM=="video4linux", BUS=="usb", SYSFS{idVendor}=="046d", SYSFS{idProduct}=="08b2", NAME="video5"

I pulled the Webcam out and back in and it went straight to /dev/video5! No more MythTV Conflicts!

tredegar · 09-25-2008, 07:37 PM

Quote:

No more MythTV Conflicts!

Good.
You got it working.
But better:
You did your own research, followed simple advice (I just pointed you at udev), but you not only found the solution on your own but then explained how, and gave good links, so others will hopefully find their solution from this thread, hopefully without having to ask anything further at all.

If your two capture cards ever start swapping their /dev/names you will now know what to do to lock them into their right places.

Happy MythTV (I gave up on that a few years ago, maybe it's time for another try. Linux gets better by the month

)

Congratulations, and thanks for the follow-up.
Have fun with linux.