GNU bug report logs - #10363
/etc/mtab -> /proc/mounts symlink affects df(1) output for /

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From: Jim Meyering <jim <at> meyering.net>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: 10363 <at> debbugs.gnu.org, coreutils <at> gnu.org
Subject: bug#10363: df vs. long-named /dev/disk/by-uuid/... file system device names
Date: Fri, 30 Dec 2011 15:00:20 +0100

Pádraig Brady wrote:

> On 12/29/2011 02:09 PM, Jim Meyering wrote:
>> On systems with recent kernel/tools, a symlink from /etc/mtab to
>> /proc/mounts, and a by-UUID mount (i.e., soon, nearly everyone),
>> you will see something like the following when running "df -hT":
>>
>>   Filesystem Type Size Used Avail Use% Mounted on
>>   rootfs rootfs 11G 1.9G 8.0G 19% /
>>   /dev/disk/by-uuid/828fc648-9f30-43d8-a0b1-f7096a2edb66 ext4 11G
>> 1.9G 8.0G 19% /
>
> Ouch.
>
> BTW, this is the first mail I've gotten about 10363?

The first message I received had these headers:

    X-Debbugs-Original-Cc: 653073 <at> bugs.debian.org, bug-coreutils <at> gnu.org
    From: jidanni <at> jidanni.org
    References: <20111224164832.GT5437 <at> codelibre.net>
    Date: Sun, 25 Dec 2011 08:40:42 +0800
    Message-ID: <874nwpzdo5.fsf_-_ <at> jidanni.org>
    Cc: 653073 <at> bugs.debian.org, 10363 <at> debbugs.gnu.org
    X-BeenThere: bug-coreutils <at> gnu.org

> I guess this is the right thing to do.
> I.E. have higher level paths in /proc/mounts, allowing
> tools that require lower level paths to traverse the links
> and pick the appropriate one.
>
> The highest level path needs to be available to do this,
> so I suppose this is appropriate in /proc/mounts,
> even though it might not be the most appropriate for
> human consumption, as can be seen above.
>
> The patch looks good.
> I guess "9" is the only questionable bit.
> On my Fedora 16 system I have in /proc/mounts:
>
>   /dev/mapper/vg_tp1-lv_root ...... /
>
> That's a fairly informative name, whereas the links further

Good point.
I've just posted a revision that replaces only /dev/disk/by-uuid/... symlinks.

> resolve to a fairly generic:
>
>   /dev/dm-2
>
> Hmm, I was contemplating using the old wrap limit of 19,
> but apart from not handling the above, using a width
> is inconsistent.  Perhaps it's better to always resolve?

I'd rather keep this minimal, since it changes the default.
Dereferencing all device symlinks seems like a job for a new option,
assuming there's sufficient justification.

> I.E. always print the base device.  It seems that one
> can work back from this anyway:
>
> $ findmnt --source /dev/dm-2
> TARGET SOURCE                     FSTYPE OPTIONS
> /      /dev/mapper/vg_tp1-lv_root ext4   rw,relatime,...

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