[aklug] Re: Friday's meeting

Quoting Tofu45 <rpelz34@acsalaska.net>:

> Mike,
>
> Please take notes of your experience.
> What works! Who had which ideas. Even what was tried that didn't work.
>
> Post on this list to share with those of us who can't make it to Friday.
> Likely someone has or will have udev/usb problems.
>
> Bob Pelz
>

Thanks Bob. I didn't get this until after my "presentation" but here =20
is what I can offer.

First of all, it was one of the most boring presentations I've ever =20
given...I almost fell asleep....

Most of the folks that came in the beginning left after I talked for =20
about 20 minutes or so...we went over the rules of how I supposed that =20
udev worked and then tried to implement some rules to see how close my =20
understanding matched reality....not very.

Thanks to the die-hards that stuck it out we discovered several things =20
(these will be obvious to someone that has used UDEV or is named Art =20
Corliss):

  - the actual mounting of the device isn't completed by udev
  - udev creates a bunch of simlinks to the "device" name...I think =20
they are hardlinks. by-id, by-uuid...looking at the rules and the dev =20
tree you can see what they are.
  - using fstab, we can change the defaults of permissions, ownership =20
and location of mount
  - If there is no label on the device and no entry in fstab, defaults =20
are used, but the current theory is that whatever is automounting that =20
device has that hardcoded...still working on that.
  - If there is a label on the device, it will mount it to the labels =20
name in the media directory
  - the command: udevinfo -q all -n /dev/<device node> will display =20
device info used in the udev rules
  - by using udev, you COULD create a device node call /dev/mynode, =20
then using fstab, mount /dev/mynode to a location with needed =20
permissions and ownership. This device rule would likely be very =20
specific using a serial numbers or some unique identifier.

This last factoid is exactly what I need to accomplish my particular =20
need....so for me this problem is resolved. However, I'm still very =20
curious to see what is automounting this device (it isn't pmount in my =20
case) and if no entry exists in fstab, how it decides where and with =20
what name to use.

Here are some non-udev specific things we learned too:
  - using mkfs.vfat label command will erase the device. Actually =20
everyone in the room believed that it would get erased, but it wasn't =20
definitive until I actually did it to see what would happen.

I'm interested in pursuing this more, so if anyone wants to post their =20
experiences, I sure would love to see what they have found.

Mike B.

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Received on Sat Jan 10 14:28:38 2009