[OT] LABEL vs UUID [was: Re: Adding a drive]
Steve Morris
samorris at netspace.net.au
Thu Apr 8 10:49:25 UTC 2010
On 08/04/10 13:41, Joe(theWordy)Philbrook wrote:
> It would appear that on Apr 7, Steve Morris did say:
>
>
>> On 06/04/10 08:23, Alan Dacey Sr. wrote:
>>
>>>> On 05/04/10 23:53, Tom H wrote:
>>>>
>>>>> Not using a UUID goes against Ubuntu standard practice (and upcoming
>>>>> Debian standard practice).
>>>>>
>>>>> It should be standard operating procedure for anyone about to embark
>>>>> on any of the above partition changes to make a note of the UUIDs (if
>>>>> she/he does not have this information saved offline) in order to
>>>>> reassign them (a very simple procedure).
>>>>>
> That's true enough Tom. But I for one never did understand why they chose to
> standardize on the NON-human readable UUID when the LABEL method, that Steve was
> suggesting, is just about as persistent.
>
> Of course I'm assuming that anyone who is going to bother manually replacing
> /dev/Xdx# references or UUID ones with LABEL should also be smart enough to make
> sure the LABELs are unique. IE: "xyzProjData01" IS preferable to "DATA" And don't
> get me started about certain distros that like to automatically label their root
> partition as just "/"...
>
>
>>> UUID's are the way to /always/ identify a particular partition. Since they should
>>> not change vey often, it really isn't much of a problem. The only time you may
>>> want to identify them by /dev/sc# is if you have a partition that you test new
>>> distros/releases on (that you want quick access to the data) and gets reformatted
>>> frequently.
>>>
> UUIDs are *_ONE_* way Alan. But LABEL is just about as persistent. Either one
> *_CAN_* be messed with by some root level processes. But as far as I know you can't
> restore the original UUID, when something does actually change it. Whether it was
> due to some resize tool as Steve suggests can happen<below> Or the way it used to
> bite me when I'd restore partition contents from an archival tarball after
> reformatting a corrupted file system. I'd have to find every place I used the old
> UUID (fstab, grub, personal admin scripts,etc... {since I multi-boot that means I
> had to find the references in the other installed Linux file systems as well.
> etc...}) and edit them all! If some errant root level process messes with my
> LABEL I *_CAN_* restore the original LABEL to the partition thus making all that
> editing unnecessary... (See my comment to Steve<below>)
>
>
>>> It also teaches you to make the right size partitions. Especially if you are lazy!
>>>
> Needs sometimes change...
>
>
>> I wasn't suggesting the use of /dev/sc# in fstab, I was suggesting the use of
>> LABEL= to identify the partition, which as far as I have been able to
>> determine is only changeable by a format. The obvious issue with UUID= is the
>> home partition where multi-user usage of applications like mail requires the
>> home partition to be resized because the original size has become too small.
>> This resizing will change the uuid, and depending on the distribution it is
>> done from and the tool used can result in a uuid that is invalid, thereby
>> making the partition unusable.
>>
> In principal I agree with you whole heartedly Steve. But there are two things I'd
> like to point out... Last one first: An invalid partition UUID is only unusable
> while your using UUID methods. Simply replace all the UUID references with LABEL
> ones and the problem is gone.
>
> First one last: Your wrong about needing to reformat a partition to
> assign a partition LABEL. (Unless your talking a swap partition that is...)
>
> Actually I can only speak from experience with ext2& ext3, But
> according to: http://manpages.ubuntu.com/manpages/karmic/man8/e2label.8.html
> e2label can also do ext4 file systems. And then there is "tune2fs -L"...
> Which I'm sure glad of because I know I can actually restore my
> original human readable partition "LABEL"(s) if any of them do get
> trashed. And there are tools out there to deal with several other
> file system types such as: reiserfs, jfs, xfs,& even ntfs...
> At least according to the wiki entry on the subject from Arch Linux:
> http://wiki.archlinux.org/index.php/Persistent_block_device_naming
> Which incidentally makes a fairly strong case for using either LABEL
> like you and I have embraced, OR UUID which I strongly dislike.
>
>
I was speaking about the label only being changeable at format time in
relation to reiserfs, which is what I mainly use. I get this impression
from the documentation for the reiserfs tools package that if I remember
correctly states explicitly that it is only changeable at format time.
The issue I had with uuid was with a swap partition. I was trying to
create 2 swap partitions which I had previously done without any issues,
and the partition manager I was using placed an invalid uuid on the
partition and refused to format it. I tried to place the 2 partitions in
a software raid 0 array but adadm complained that the uuid was invalid
and refused to touch it. If I manually placed an entry in fstab for this
swap partition and specified the uuid that the partition manager
displayed the system refused to use it, and if I used the /dev/sdx
specification the system still refused to use it as a swap partition.
regards,
Steve
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