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Label multimeanings : doc bug?

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  Label multimeanings : doc bug? Rusi Mody <rustompmody@gmail.com> - 2019-02-27 07:20 +0100
    Re: Label multimeanings : doc bug? Reco <recoverym4n@enotuniq.net> - 2019-02-27 07:40 +0100
      Re: Label multimeanings : doc bug? Rusi Mody <rustompmody@gmail.com> - 2019-02-27 08:30 +0100
      Re: Label multimeanings : doc bug? Rusi Mody <rustompmody@gmail.com> - 2019-02-27 08:30 +0100
        Re: Label multimeanings : doc bug? Reco <recoverym4n@enotuniq.net> - 2019-02-27 10:00 +0100
          Re: Label multimeanings : doc bug? Richard Hector <richard@walnut.gen.nz> - 2019-02-27 19:00 +0100
            Re: Label multimeanings : doc bug? Pascal Hambourg <pascal@plouf.fr.eu.org> - 2019-02-27 21:30 +0100
      Re: Label multimeanings : doc bug? Andy Smith <andy@strugglers.net> - 2019-02-28 04:40 +0100

#205771 — Label multimeanings : doc bug?

Ref: This stackexchange post: 
https://unix.stackexchange.com/q/503241/323121 

Context: Theres this guy who's really struggling with disk partitioning LVM etc concepts.  That point is not directly relevant to this question. 

My answer on that post tries to clarify that 'label' can mean 3 things at least; 
and that just in the context of disks, partitions etc. Quite confusing!! 

My question: In his parted output he has 

Error: /dev/mapper/lubuntu--vg-home: unrecognised disk label 

In which sense is this 'label' used?? 

Is it the Open/Free-BSD sense? Or the partition label sense? 

And if the first should it not be (something like) partition table?

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#205772

	Hi.

On Tue, Feb 26, 2019 at 10:02:24PM -0800, Rusi Mody wrote:
> My question: In his parted output he has 
> 
> Error: /dev/mapper/lubuntu--vg-home: unrecognised disk label 
> 
> In which sense is this 'label' used?? 

In this context, a disklabel is a "partition table type", like "msdos"
or "gpt" or "sun".
Running parted on a logical volume is definitely not the best of ideas.

Reco

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#205774

And the space between "disk" and "label" hardly helps any! 

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#205775

Reco wrote:
Running parted on a logical volume is definitely not the best of ideas

Sure! 

My point was however that for a tool (eg gparted) where label already has the LABEL= sense this other (disklabel) terminology, more common in the BSD world, seems to be an avoidable confusion.

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#205776

	Hi.

On Tue, Feb 26, 2019 at 11:12:43PM -0800, Rusi Mody wrote:
> Reco wrote:
> Running parted on a logical volume is definitely not the best of ideas
> 
> Sure! 
> 
> My point was however that for a tool (eg gparted) where label already has the LABEL= sense this other (disklabel) terminology, more common in the BSD world, seems to be an avoidable confusion.

I see nothing to be confused about.
A disklabel, as they call it in parted(8) applies to a disk device. Or a LUN.

A LABEL= is a filesystem attribute, it's impossible to have one without a filesystem.

Reco

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#205786

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On 27/02/19 9:57 PM, Reco wrote:
> 	Hi.
> 
> On Tue, Feb 26, 2019 at 11:12:43PM -0800, Rusi Mody wrote:
>> Reco wrote:
>> Running parted on a logical volume is definitely not the best of ideas
>>
>> Sure! 
>>
>> My point was however that for a tool (eg gparted) where label already has the LABEL= sense this other (disklabel) terminology, more common in the BSD world, seems to be an avoidable confusion.
> 
> I see nothing to be confused about.
> A disklabel, as they call it in parted(8) applies to a disk device. Or a LUN.
> 
> A LABEL= is a filesystem attribute, it's impossible to have one without a filesystem.

It appears that GPT also supports a partition label, separate from any
filesystem label, and different from a BSD disklabel.

Richard

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#205789

Le 27/02/2019 à 18:53, Richard Hector a écrit :
> On 27/02/19 9:57 PM, Reco wrote:
>>
>> A disklabel, as they call it in parted(8) applies to a disk device. Or a LUN.

Or any other partitionable block device, such as a software RAID array 
or a loop device.

>> A LABEL= is a filesystem attribute, it's impossible to have one without a filesystem.

A swap area can have a LABEL but is not a filesystem.

> It appears that GPT also supports a partition label, separate from any
> filesystem label, and different from a BSD disklabel.

In blkid terminology this is called PARTLABEL (along with PARTUUID) to 
distinguish them from filesystem LABEL/UUID.

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#205794

Hello,

On Wed, Feb 27, 2019 at 09:37:58AM +0300, Reco wrote:
> Running parted on a logical volume is definitely not the best of ideas.

As an aside, I do this all the time and it works fine.

The logical volumes are exported to virtual machines as their main disk,
so they may appear as /dev/vgname/lvname on the host which when
partitioned and presented to a guest will show as /dev/xvda{1,2,…}.

If I want to later manipulate the partition table from outside the
guest I may run parted on the /dev/vgname/lvname.

Similar is expected to work on disk image files.

Direct access in the host to the partitions on such a thing as block
devices can be enabled by using kpartx (or fiddling with offsets in
losetup, but life is too short!).

Cheers,
Andy

-- 
https://bitfolk.com/ -- No-nonsense VPS hosting

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