UUID

Tue Dec 30 22:42:17 MST 2014

Welp, I went and installed a linux mint vm and see that grub.cfg has the
root pointed at hd0 and a big fat UUID.  Gotta love it.  The lesson here is
if you're playing with your partitions, rerun the grub stuffs.

On Tue, Dec 30, 2014 at 9:38 PM, Michael Havens <bmike1 at gmail.com> wrote:

> so then why did his virtual machine not look at the partitions as UUIDs
> but rather as /dev/sd?? ?
>
> :-)~MIKE~(-:
>
> On Tue, Dec 30, 2014 at 9:29 PM, James Mcphee <jmcphe at gmail.com> wrote:
>
>> Hrmph, I guess you don't need one these days.  I'm working off an old
>> system that's been upgraded since the bronze age.
>>
>> https://www.gnu.org/software/grub/manual/html_node/Device-map.html
>>
>> On Tue, Dec 30, 2014 at 9:13 PM, Michael Havens <bmike1 at gmail.com> wrote:
>>
>>> I suppose not..... so where are UUID and  logical addresses kept?
>>>
>>> :-)~MIKE~(-:
>>>
>>> On Tue, Dec 30, 2014 at 9:04 PM, Michael Havens <bmike1 at gmail.com>
>>> wrote:
>>>
>>>> well I thought to myself that I should investigate the file before
>>>> asking any questions but:
>>>>
>>>>  cat /boot/grub/device.map
>>>> cat: /boot/grub/device.map: No such file or directory
>>>>
>>>> I then reasoned that I would play the <tab><tab> game and see what the
>>>> files were in /boot/grub .
>>>>
>>>> grub.cfg  grubenv
>>>>
>>>> so I suppose it is grub.cfg?
>>>>
>>>> :-)~MIKE~(-:
>>>>
>>>> On Tue, Dec 30, 2014 at 8:27 PM, James Mcphee <jmcphe at gmail.com> wrote:
>>>>
>>>>> /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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>>>>>
>>>>
>>>>
>>>
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>>
>>
>> --
>> James McPhee
>> jmcphe at gmail.com
>>
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-- 
James McPhee
jmcphe at gmail.com
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