drive <-> device mapping

I have four USB thumb drives, which are marked 1-4 but otherwise identical.
How do I get udev to assign them the same /dev/ entries every time it
notices them?

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You must either use dongles, different makes of drives with different
product ID's (PID) or different VID's (vendor ID's), or use full usb 3.1
devices and ports that are required to have serial numbers...but that is
not exactly followed.
Try looking for the iSerialNumber field in the USB device descriptor.  
If there is one, it is supposed to be unique.
  Other than that, I have no idea.
The bit from the udev rules that kicked me away from trying something
like this:


      Matching sysfs attributes

The match keys introduced so far only provide limited matching
capabilities. Realistically we require much finer control: we want to
identify devices based on advanced properties such as vendor codes,
exact product numbers, serial numbers, storage capacities, number of
partitions, etc.

Many drivers export information like this into sysfs, and udev allows us
to incorporate sysfs-matching into our rules, using the /ATTR/ key with
a slightly different syntax.

Here is an example rule which matches a single attribute from sysfs.
Further detail will be provided later in this document which will aid
you in writing rules based on sysfs attributes.

    SUBSYSTEM=="block", ATTR{size}=="234441648", SYMLINK+="my_disk"



On 2/2/2016 12:31 PM, Eben King wrote:
> I have four USB thumb drives, which are marked 1-4 but otherwise
> identical. How do I get udev to assign them the same /dev/ entries
> every time it notices them?
>

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Have you used udevinfo to list the properties for each?  See any
differences at all between them?  If so, (unless it is just a disk error
rate) then you can use that to write udev rules, right?

On 2/2/2016 12:31 PM, Eben King wrote:
> I have four USB thumb drives, which are marked 1-4 but otherwise
> identical. How do I get udev to assign them the same /dev/ entries
> every time it notices them?
>
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On Tue, 2 Feb 2016, Art Eaton wrote:

> On 2/2/2016 12:31 PM, Eben King wrote:
>> I have four USB thumb drives, which are marked 1-4 but otherwise identical.
>> How do I get udev to assign them the same /dev/ entries every time it
>> notices them?

> Have you used udevinfo to list the properties for each?

Don't appear to have it:

eben@pc:~$ udevinfo -h
udevinfo: command not found
eben@pc:~$ locate udevinfo
eben@pc:~$

Synaptic doesn't have it, but lsusb -v (as root) gave up the goods:

1:  iSerial                 3 P16000160703617A05473776
2:  iSerial                 3 P1600016070361880F9D2F69
3:  iSerial                 3 P16000160703617A170AB796
4:  iSerial                 3 P16000160703617A21EC8E37

> you can use that to write udev rules, right?

I can figure out how.  Probably.

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much more talented than you.  Laughter is the very best medicine,
remember that when your appendix bursts next week.  -- Weird Al
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Looks like iSerial came through for you.  You are lucky I think.

On 2/2/2016 2:24 PM, Eben King wrote: _______________________________________________
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On Tue, 2 Feb 2016, Eben King wrote:

Yup:

ATTRS{serial}=="P16000160703617A05473776",SYMLINK="raid_1"
ATTRS{serial}=="P1600016070361880F9D2F69",SYMLINK="raid_2"
ATTRS{serial}=="P16000160703617A170AB796",SYMLINK="raid_3"
ATTRS{serial}=="P16000160703617A21EC8E37",SYMLINK="raid_4"

If something else pops up with one of those serials it breaks the RAID, but
it's highly unlikely that'll happen.

Odd that it wants ATTRS{serial} and not ATTRS{iSerial}, but I guess it's
going for the (unstated) logical name instead.

--
-eben    [hidden email]    ebmanda.redirectme.net:81
LIBRA:  A big promotion is just around the corner for someone
much more talented than you.  Laughter is the very best medicine,
remember that when your appendix bursts next week.  -- Weird Al
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