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Old 08-14-2008, 03:50 AM
Smoot Carl-Mitchell
 
Default UUIDs on drives (was Hibernate on batery low)

On Thu, 2008-08-14 at 12:23 +0930, Brian Astill wrote:
> On Thursday 14 August 2008 09:47:49 Rashkae wrote:
> > I've never seen any problems
> > reported with the use of UUID that doesn't amount to old school
> > gurus not wanting to learn something different.
>
> That's incorrect - unless you haven't been looking!
> If there is a key to unravel the info implicit in /dev/hdb3
> (Primary partition on the Slave drive) from its UUID, would
> someone please publish it.
>
> Also, would someone please tell me how to construct a UUID for a
> partition I have just created - short of rebooting and seeing if
> I can identify it from fstab, assuming the partition is mounted.

You can display the UUID with the blkid program:

sudo blkid /dev/sda1
>
> Why is a simple 8-digit code sufficient to uniquely identify a
> vfat partition, eg "UUID=3FF4-3BE7 /media/hda1 vfat"
> whereas a Linux partition needs something HUGE
> UUID=d757b47c-5808-4271-a247-9df9072826de /media/hdb1 ext2

UUIDs are suppose to be universally unique. Generating a random 16 byte
number is probably sufficient to make a UUID universally unique. The
probability of a duplicate is 1 chance in 2**128 which is very unlikely.
4 bytes is not going to be universally unique. I am not sure why vfat
partitions only have 4 byte UUIDs.

--
Smoot Carl-Mitchell
System/Network Architect
smoot@tic.com
+1 480 922 7313
cell: +1 602 421 9005

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Old 08-14-2008, 04:18 AM
Rashkae
 
Default UUIDs on drives (was Hibernate on batery low)

Brian Astill wrote:
> On Thursday 14 August 2008 09:47:49 Rashkae wrote:
>> I've never seen any problems
>> reported with the use of UUID that doesn't amount to old school
>> gurus not wanting to learn something different.
>
> That's incorrect - unless you haven't been looking!
> If there is a key to unravel the info implicit in /dev/hdb3
> (Primary partition on the Slave drive) from its UUID, would
> someone please publish it.

huh?


>
> Also, would someone please tell me how to construct a UUID for a
> partition I have just created - short of rebooting and seeing if
> I can identify it from fstab, assuming the partition is mounted.
>

create a file system,, they all get a fresh new UUID. you can
change/create a new UUID with the filesystem utilities if you want.
(like tune2fs, I believe, for ext3)


> Why is a simple 8-digit code sufficient to uniquely identify a
> vfat partition, eg "UUID=3FF4-3BE7 /media/hda1 vfat"
> whereas a Linux partition needs something HUGE
> UUID=d757b47c-5808-4271-a247-9df9072826de /media/hdb1 ext2
>

More bits = less chance accidentally duplicating a UUID from random
creation.


> I could go on, but please notice that change does not always
> involve progress.
>


Plonk? Not yet, as I understand your frustration. Though I greatly
disagree with your opinion, in this instance.. I deal with system that
have several hard drives on multiple controllers.. I assure you, this
change is not only progress,, it's outright necessity.

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Old 08-14-2008, 04:20 AM
Rashkae
 
Default UUIDs on drives (was Hibernate on batery low)

Smoot Carl-Mitchell wrote:

>
> UUIDs are suppose to be universally unique. Generating a random 16 byte
> number is probably sufficient to make a UUID universally unique. The
> probability of a duplicate is 1 chance in 2**128 which is very unlikely.
> 4 bytes is not going to be universally unique. I am not sure why vfat
> partitions only have 4 byte UUIDs.
>

Has to be said, sorry.

Four bytes should be enough memory for anyone.

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Old 08-14-2008, 06:07 AM
Mario Vukelic
 
Default UUIDs on drives (was Hibernate on batery low)

On Thu, 2008-08-14 at 12:23 +0930, Brian Astill wrote:
> Also, would someone please tell me how to construct a UUID for a
> partition I have just created

https://help.ubuntu.com/community/UsingUUID


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Old 08-14-2008, 01:06 PM
Derek Broughton
 
Default UUIDs on drives (was Hibernate on batery low)

Brian Astill wrote:

> On Thursday 14 August 2008 09:47:49 Rashkae wrote:
>> I've never seen any problems
>> reported with the use of UUID that doesn't amount to old school
>> gurus not wanting to learn something different.
>
> That's incorrect - unless you haven't been looking!

I've been looking, and completely agree with Rashkae.

> If there is a key to unravel the info implicit in /dev/hdb3
> (Primary partition on the Slave drive) from its UUID, would
> someone please publish it.

There is no "info" implicit in the UUID - it's just a nearly unique
identifier.

>
> Also, would someone please tell me how to construct a UUID for a
> partition I have just created - short of rebooting and seeing if
> I can identify it from fstab, assuming the partition is mounted.

While it's strictly just a bit string in the superblock - and so writeable
if you know what you're doing - a UUID is generally created by mkfs
automatically. So you _don't_ construct a UUID, you construct an fstab
entry from the known UUID.

> Why is a simple 8-digit code sufficient to uniquely identify a
> vfat partition, eg "UUID=3FF4-3BE7 /media/hda1 vfat"

It's not. The intent is to be "nearly" unique.

> whereas a Linux partition needs something HUGE
> UUID=d757b47c-5808-4271-a247-9df9072826de /media/hdb1 ext2
>
> I could go on, but please notice that change does not always
> involve progress.

You haven't shown us anything to disabuse us of the notion that your only
problem is not wanting to learn something different. UUID was not
introduced to initiate progress - it was introduced to _deal_ with
progress.
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