This series is written by a representative of the latter group, which is comprised mostly of what might be called "productivity users" (perhaps "tinkerly productivity users?"). Though my lack of training precludes me from writing code or improving anyone else's, I can, nonetheless, try and figure out creative ways of utilizing open source programs. And again, because of my lack of expertise, though I may be capable of deploying open source programs in creative ways, my modest technical acumen hinders me from utilizing those programs in what may be the most optimal ways. The open-source character, then, of this series, consists in my presentation to the community of open source users and programmers of my own crude and halting attempts at accomplishing computing tasks, in the hope that those who are more knowledgeable than me can offer advice, alternatives, and corrections. The desired end result is the discovery, through a communal process, of optimal and/or alternate ways of accomplishing the sorts of tasks that I and other open source productivity users need to perform.

Saturday, March 8, 2014

Miscellaneous Saturday quickies: udev rules and you

PREFACE: "udev is a device manager for the Linux kernel. Primarily, it manages device nodes in /dev. It is the successor of devfs and hotplug, which means that it handles the /dev directory and all user space actions when adding/removing devices, including firmware loading." (Wikipedia entry for udev) Those wanting a better orientation to udev may wish to do some further reading of material found at some of the links provided in this entry.
I felt a great sense of triumph when, oh, 5 or 6 years ago, I managed to create a udev rule that would make a scanner I was trying to use be identified in a certain way to the system. In the wake of that project I was also able to craft some udev rules for some external hard drives I was using. Since then, I've learned, however, that computer tech is a quickly moving target; the things I took such great pains to learn and apply back then, as I now know, might be of little use to me in just a few short years.

Case in point: fast forward to yesterday, when, after a Mythtv/Mythbuntu upgrade, one of the capture cards I'd written a udev rule for was no longer being properly identified to the system. The reason being, of course, that some changes had been made to udev conventions and the old trick I'd used to identify that card to the system was no longer working.

So I had to rewrite the rule. It turns out some parts of the routine for identifying and naming devices have been a bit simplified. The new incantation I needed to run to find out details about the catpure card which I could incorporate into the udev rule goes like this:



(where sdb is replaced by the device name of the hardware you're querying--in my case, video0)

That bit was lifted from a 2009 entry from a blog located here. He references an even older web page as a source for his information, one I'd used in my first attempts 5 or 6 years ago, and which looks to be pretty outdated now. That page is called "recativated" and can be found here.

In any case, an even simpler rendition of the incanation above is offered in the "comments" section of that blog, as follows:



Both gave the results I needed and helped me resolve the issue of the card being identified and labelled as I wanted it to be. Maybe this information will be useful to you as well--at least so long as you find and try to apply it before the next big change comes to udev, or udev gets superseeded by some other, "better" utility.
Posted by at 4:23 PM
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