:: [DNG] Fwd: For all you automounter…
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Author: Jim Murphy
To: dng
Subject: [DNG] Fwd: For all you automounter programmers
Sorry for forward everyone, forgot to send to list.

---------- Forwarded message ----------
From: Jim Murphy <srlinuxadmin@???>
Date: Tue, May 3, 2016 at 7:06 AM
Subject: Re: [DNG] For all you automounter programmers
To: Didier Kryn <kryn@???>

On Tue, May 3, 2016 at 4:04 AM, Didier Kryn <kryn@???> wrote:
> Le 02/05/2016 14:12, fsmithred a écrit :
>> No support for file system labels at this time. If someone can tell me a
>> reliable way for unprivileged user to get the labels, I'll add it. Feel
>> free to use these scripts as they are or as motivation to create something
>> better.
>> -fsr
>> On 04/28/2016 01:52 PM, fsmithred wrote:
>>> On 04/27/2016 08:28 PM, fsmithred wrote:
>>>> You could get the label from lsblk, do 'pmount label' and it will be
>>>> mounted at /media/label. Every time you plug in a thumb drive labeled
>>>> backup, it'll go to the same place. If you unmount the drive,
>>>> /media/label
>>>> will no longer exist, so you could even have the backup script check to
>>>> make sure it's there.
>>>> -fsr
>>> Correction - Only root can get the label from lsblk. User can get the
>>> label from '/sbin/blkid -s LABEL', but only after root has run blkid at
>>> least once. Other than that, I've now got a script that will handle the
>>> labels... sometimes.
>>> -fsr
> kryn@apcnb98:~$ /sbin/blkid /dev/sda5
> /dev/sda5: LABEL="/" UUID="d91acaa3-5fdc-49e9-9f2b-ba7f3efb33f9"
> UUID_SUB="6a0c80cd-5dc6-4135-8018-575686e7e11e" TYPE="btrfs"
> kryn@apcnb98:~$ /sbin/blkid /dev/sda6
> /dev/sda6: LABEL="/usr" UUID="05f9f811-b8b1-445f-ac8c-9537a202a9f9"
> UUID_SUB="52b8e1b8-7080-4696-94e1-8f7580005871" TYPE="btrfs"
>     Didier

Problem, blkid uses a cache that is only updated when root runs blkid.
Any changes are not automatically updated. A user only sees the cache.

The issues is, fsr is trying to do everything as a "user" so tools like
lsblk and blkid don't work for this case. For blkid, the cache will not
be up to date when say a flash-drive is add/or removed.