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From: Geoff Clements on 20 Apr 2010 13:51
Bruce Richardson wrote:

> Dave Gibson <dave+news002(a)gibson-hrd.abelgratis.co.uk.invalid> wrote:
>>
>> Plug the devices in and use '/lib/udev/vol_id --uuid' to determine the
>> UUID of each filesystem on the devices:
>>
>
> Surprised nobody has yet mentioned udevinfo, which will give plenty of
> contextual information to choose from. Try something like
>
> udevinfo --query=all --name=sdb1
>
> And you'll see many things you could use in a rule.
>
>

or on debian testing:

udevadm info --query=all --name=sdb1

--
Geoff
From: Geoff Clements on 19 Apr 2010 13:48
R. Georgeson wrote:

> I want to plug a camera and a USB external disc into a laptop and download
> from one to t'other. ATM it sees whichever is plugged in first as sdb and
> the second as sdc. What I'd like is to have eg the camera as sdc1 and the
> USB disc as sdbn whether or not the other is connected so I can set up the
> fstab and the symlinks to make it all easy.
>
> I started looking at udev and it's rules, seemed a likely place to start,
> but didn't understand it much, actually to be honest, at all.
>

If you want particular device names then udev rules are the way to go, have
a look at:
http://reactivated.net/writing_udev_rules.html

But usually just setting up the correct mount point is good enough. Most
modern distros will mount the USB disk under:
/media/<label>
where <label> is the filesystem label of the disk.

Assuming they are vfat filesystems (they usually are but not always) you can
read/set the filesystem label with the dosfslabel command as root.

--
Geoff
From: alexd on 19 Apr 2010 14:43
On 19/04/10 16:48, R. Georgeson wrote:
> I want to plug a camera and a USB external disc into a laptop and download
> from one to t'other. ATM it sees whichever is plugged in first as sdb and
> the second as sdc. What I'd like is to have eg the camera as sdc1 and the
> USB disc as sdbn whether or not the other is connected so I can set up the
> fstab and the symlinks to make it all easy.
>
> I started looking at udev and it's rules, seemed a likely place to start,
> but didn't understand it much, actually to be honest, at all.

Yeah, I had a go at that once well for a similar scenario and couldn't
get anywhere with it. I wanted to kick off a mount + rsync + unmount
backup script when a suitably-labelled drive was plugged in. Gave up in
the end and now cron does it instead. I just couldn't get udev to do
anything upon a device plug in event.

Have a look in /dev/disk/by-*

You will find each mass storage device has one or more unique handles
you can mount it by, possibly including as mentioned elsethread, a
label. You can set labels on extN filesystems with e2label.

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From: Dave Gibson on 19 Apr 2010 15:23
R. Georgeson <rmg(a)nospam.zen.uk> wrote:
> I want to plug a camera and a USB external disc into a laptop and download
> from one to t'other. ATM it sees whichever is plugged in first as sdb and
> the second as sdc. What I'd like is to have eg the camera as sdc1 and the
> USB disc as sdbn whether or not the other is connected so I can set up the
> fstab and the symlinks to make it all easy.
>
> I started looking at udev and it's rules, seemed a likely place to start,
> but didn't understand it much, actually to be honest, at all.

Plug the devices in and use '/lib/udev/vol_id --uuid' to determine the
UUID of each filesystem on the devices:

# /lib/udev/vol_id --uuid /dev/sdb1
aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa
# /lib/udev/vol_id --uuid /dev/sdb2
bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb
# /lib/udev/vol_id --uuid /dev/sdc1
XXXX-XXXX

Add entries to /etc/fstab specifying those uuids in the first field
instead of the device names:

UUID=aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa /media/u1 auto noauto,user 0 0
UUID=bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb /media/u2 auto noauto,user 0 0
UUID=XXXX-XXXX /media/cam auto noauto,user 0 0

Use the mount-point names when mounting and umounting the filesystems.

Reformatting a filesystem will change its uuid so /etc/fstab will need
to be updated.
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