UUID
Michael Havens
bmike1 at gmail.com
Tue Dec 30 23:33:06 MST 2014
James, I'm so sorry I didn't inspect grub.cfg more closely. You said that
grub.cfg maps the logical addresses to the UUID. Is the logical address the
'efi=hd0,msdos1' and/or the 'ahci0,msdos1'? (I am guessing
that hd0,msdos1/ahci0,msdos1 is sda1) (more to my mail after the output of
the following cat)
(from my os)
cat /boot/grub/grub.cfg
menuentry 'Linux Mint 17.1 MATE 64-bit, 3.13.0-37-generic (/dev/sda1)'
--class ubuntu --class gnu-linux --class gnu --class os {
recordfail
gfxmode $linux_gfx_mode
insmod gzio
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1
--hint-efi=hd0,msdos1
--hint-baremetal=ahci0,msdos1 f35e1797-4cdb-4930-a740-b424afbf61c7
else
search --no-floppy --fs-uuid --set=root
f35e1797-4cdb-4930-a740-b424afbf61c7
fi
linux /boot/vmlinuz-3.13.0-37-generic
root=UUID=f35e1797-4cdb-4930-a740-b424afbf61c7 ro quiet splash $vt_handoff
initrd /boot/initrd.img-3.13.0-37-generic
}
All of this is intriguing however it still leaves my question unanswered. I
believed that UUIDs would allow a partition to be placed anywhere on the
disk and things would continue as normal. I now believe that to not be the
case. What is the ultimate purpose of a UUID?
:-)~MIKE~(-:
On Tue, Dec 30, 2014 at 10:42 PM, James Mcphee <jmcphe at gmail.com> wrote:
> 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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>>
>>
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>
>
>
> --
> James McPhee
> jmcphe at gmail.com
>
> ---------------------------------------------------
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>
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