slow booting after installation of another Linux

[Christopher Browne]

n Mon, Oct 8, 2012 at 12:25 PM, Kevin Cozens <kevin-4dS5u2o1hCn3fQ9qLvQP4Q at public.gmane.org> wrote:
> D. Hugh Redelmeier wrote:
>>
>> Spoiler:
>> The problem was that I let the new installation reformat the swap
>> partition.  In the process, it gave it a new UUID.  That means that
>> the fstab entries on the old system referred to the partition by a
>> UUID that no longer existed or worked.
>
>
> It is also why I avoid using UUID's in fstab.

I'd not think that the fault of this is the use of UUIDs; the UUID is
just a label constructed with a reasonable expectation of uniqueness.

Is the problem with UUID usage that:
a) They're bad labels?  That seems unlikely; they're not memorable,
but that's not unintentional.

b) The use of a label is bad?  Again, I don't think so.  The emergence
of dynamic disk-like devices, and lots potentially on buses, means
that we can no longer expect particular stability of /dev/sda being
the same device from one bootup to the next.

I suppose it's somewhat nice if one can arrive at labels that are
human interpretable; that's likely to make them easier to organize.
But Linux distributions have to cope with there being humans that
don't even know there's some reason to attach a label.

We have plenty of cases already where people are forced to make up
encodings; adding more isn't an obvious feature.  (A "forced to" case
is with local networks.  What's 192.168.0.1 to you? :-))

I'm being bitten by an edge case on the "UUID/label" thing, lately.  I
have been trying out BTRFS, and, with there being no guarantee that
the disks on the "BTRFS array" will forcibly be /dev/sdc and /dev/sdd,
I'm not able to consistently able to get the BTRFS filesystem to mount
at boot time.

There is a labelling command for BTRFS...
$ btrfs filesystem label /dev/sdc my-favorite-label

is *supposed* to work, but has a strange constraint that seems to make
this useless.

              NOTE: Currently there are the following limitations:
              - the filesystem has to be unmounted
              - the filesystem should not have more than one device.

I merged two disks into the filesystem, so my system 'fails' on the
latter aspect.  Mind you, there's something odd about the failure.
Note it doesn't say what kind of failure will take place under the >1
device condition.

wolfe:~# btrfs filesystem show
Label: '3463deb0-0a63-11e2-b113-0013d4789ffa'  uuid:
396ae2ef-a891-4a8d-8ee7-543bcc069ec9
        Total devices 2 FS bytes used 3.55TB
        devid    2 size 1.82TB used 1.82TB path /dev/sdd
        devid    1 size 1.82TB used 1.82TB path /dev/sdc

Btrfs Btrfs v0.19

It appears as though I have not one, but two labels attached to my
favorite large filesystem.  But if I set up a
UUID=... /brownes/wolfe/btrfs btrfs defaults
entry in /etc/fstab, mount doesn't seem happy about recognizing this.

[Mumble, looking at "man mount"]

Perhaps I should instead look at LABEL=, if I assigned a label...

Heh.  That did the trick!

LABEL=3463deb0-0a63-11e2-b113-0013d4789ffa /brownes/wolfe/btrfs btrfs defaults

--> mount /brownes/wolfe/btrfs
now works as expected...

There's something that's a pain about this; it seems to me as though
we don't need both a LABEL and UUID to label a filesystem.  Rather,
UUID seems like a way to automatically generate a label for those that
don't want to expend though on label generation.
-- 
When confronted by a difficult problem, solve it by reducing it to the
question, "How would the Lone Ranger handle this?"
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