UUID

[James Mcphee]

/boot/grub/device.map keeps things mapped by logical location and uuid.  if
you created a new partition, even if it had the same UUID, it would have a
different logical address.

On Tue, Dec 30, 2014 at 7:41 PM, Michael Havens <bmike1 at gmail.com> wrote:

> better yet could someone come explain it to us:
>
> http://www.bleepingcomputer.com/forums/t/561405/new-partition-scheme/page-2#entry3582631
>
> :-)~MIKE~(-:
>
> On Tue, Dec 30, 2014 at 7:38 PM, Michael Havens <bmike1 at gmail.com> wrote:
>
>> I'm part of another discussion in which we are talking about UUIDs.
>> This is what one of the participants said:
>>
>> As pointed out earlier by bmike1 in response to my comment about GRUB2
>> not being able to find the OS if you move the partitions, by default on
>> Linux Mint GRUB2 will use UUIDs *(the id tag for your partitions)* instead
>> of partition numbers*(eg: sda1, sda2, etc)*, so I was incorrect when I
>> said GRUB2 won't be able to find the boot partition. Linux Mint's fstab *(a
>> config file read at boot to tell Mint which partitions should be
>> automatically mounted)* also uses UUIDs by default so no issues there.
>> Therefore I do not see any reason why moving your installation would be an
>> issue *(keep reading)*, so I decided to test it in a virtual machine. I
>> installed Linux Mint 17.1 - Cinnamon 64bit *(I've been wanting to try
>> Linux Mint for a while. I've been downloading a little bit of the ISO each
>> day)* with a partition layout similar to yours *(http://i.imgur.com/3qg0bSv.png
>> <http://i.imgur.com/3qg0bSv.png> )*. I wasn't able to move the extended
>> partition using Gparted, or create a new one. In the end I just created 3
>> new primary partitions and cloned the Linux Mint logical partitions to them
>> using dd *(dd is a sector based cloning tool that comes pre-installed on
>> most Linux operating systems. I used it because this way the new partitions
>> will have the same UUIDS as the Linux Mint ones did. This is important
>> since GRUB2 is using UUIDS to identify the boot partition and because the
>> fstab uses UUIDs to identify your swap partition)*. Then I deleted the
>> old partitions *( http://i.imgur.com/hDBT5ns.png
>> <http://i.imgur.com/hDBT5ns.png> )*. The result was that GRUB2 was
>> unable boot Linux Mint because it couldn't find the boot partition *(I
>> don't know why this is, but if I had to take a guess it would be that GRUB2
>> was probably storing part of itself on the extended partition's VBR which
>> no longer exists because I deleted the extended partition)*. So GRUB2
>> needed to be repaired. Using a Linux Mint Live-cd, I ran "sudo
>> add-apt-repository ppa:yannubuntu/boot-repair"*(this adds a third party
>> repo that has boot-repair in it, because it's not available in the default
>> Linux Mint repos)*, "sudo apt-get update" *(to update apts package list)*,
>> "sudo apt-get install boot-repair" *(to download and install
>> boot-repair)*, and then I ran boot-repair with its default settings *(be
>> warned by default boot-repair uploads information about your computer
>> online, you can disable this)*. This successfully fixed GRUB2, and I was
>> able to boot Linux Mint again *(http://i.imgur.com/ZJhXRbe.png
>> <http://i.imgur.com/ZJhXRbe.png> )*.
>>
>> I then said:
>>
>> I think I know why it needed repairing. The reason is that you created
>> new partitions (new UUIDs) and deleted the old partitions (the existing
>> UUIDs).
>>
>> to which he responded:
>>
>> The partitions were cloned with dd so that they would have the same
>> UUIDs. I also used "sudo blkid" to verify the uuids of the new primary
>> partitions matched before deleting the original logical partitions.
>>
>> He and I both remarked between the first and last quote that we thought
>> the UUID of the partition would of had it recognized regardless of what we
>> did with other partitions on the drive. Could someone kindly explain to us
>> wherein the difficulties lie?
>> :-)~MIKE~(-:
>>
>
>
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-- 
James McPhee
jmcphe at gmail.com
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