Hi there, In the process of setting up webcams (and getting greatly frustrated) I have been using mknod to create device entries. This is something I'm not really familiar with and I have some questions. I am trying things at present and don't really know why I am typing stuff I find in Google! Questions: 1) How are major and minor device numbers assigned? e.g. a webpage will say type "mknod /dev/video0 c 81 0". I understand the syntax but why 81 and 0 for the major and minor numbers? 2) How do these devices you create interact with udev? Permissions and other things seem to disappear after a reboot. Should I be using udev instead of mknod? URLs to articles would be appreciated or just people's comments. I promise to Wiki what I find out as I have been doing for most of my discoveries... Ian
On Fri, Sep 23, 2005 at 10:54:29AM +1200, Ian McDonald wrote:
Hi there,
Questions: 1) How are major and minor device numbers assigned? e.g. a webpage will say type "mknod /dev/video0 c 81 0". I understand the syntax but why 81 and 0 for the major and minor numbers?
Listed in /usr/src/linux/Documentation/devices.txt
2) How do these devices you create interact with udev? Permissions and other things seem to disappear after a reboot. Should I be using udev instead of mknod?
Yes. most distros these days seem to put /dev on a "tmpfs" memory-only mount, so it gets regenerated by udev each boot. You shouldn't need to use mknod manually; udev makes device files for all the detected devices attached to your system if you have kernel support for them. What type of webcams are you having problems with?
URLs to articles would be appreciated or just people's comments. I promise to Wiki what I find out as I have been doing for most of my discoveries...
There are a few articles linked to from www.wlug.org.nz/UDev John
John, Comments in-line On 23/09/05, John R. McPherson <jrm21(a)cs.waikato.ac.nz> wrote:
On Fri, Sep 23, 2005 at 10:54:29AM +1200, Ian McDonald wrote:
Hi there,
Questions: 1) How are major and minor device numbers assigned? e.g. a webpage will say type "mknod /dev/video0 c 81 0". I understand the syntax but why 81 and 0 for the major and minor numbers?
Listed in /usr/src/linux/Documentation/devices.txt
Thanks.
2) How do these devices you create interact with udev? Permissions and other things seem to disappear after a reboot. Should I be using udev instead of mknod?
Yes. most distros these days seem to put /dev on a "tmpfs" memory-only mount, so it gets regenerated by udev each boot. You shouldn't need to use mknod manually; udev makes device files for all the detected devices attached to your system if you have kernel support for them.
OK.
What type of webcams are you having problems with?
A firewire one from OrangeMicro (iBot) and a Dick Smith one which is ov51x based. (NB I haven't tried your code yet mentioned in Wiki as trying to get it working with Video4Linux at present)
URLs to articles would be appreciated or just people's comments. I promise to Wiki what I find out as I have been doing for most of my discoveries...
There are a few articles linked to from www.wlug.org.nz/UDev
Cool. I will add some general comments.
John
Ian
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Ian McDonald -
John R. McPherson