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Re: Grub installation may get erroneous after a hardware reconfiguration

From: Vladimir 'φ-coder/phcoder' Serbinenko
Subject: Re: Grub installation may get erroneous after a hardware reconfiguration
Date: Tue, 19 Mar 2013 14:56:41 +0100
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On 19.03.2013 10:14, Arbiel (gmx) wrote:

> Hi
> Enclosed are two numbered files, generated on my own PC.
> blkid.numbered, for displaying uuids
> grub.cfg.numbered, generated when I installed a Ubuntu distribution on
> an external device dedicated to get the internal drive of another PC
> used at a place without Internet connection.
> At the other place, grub stopped running when it got at line 62, because
> it did not find any 'hd1,msdos5' device, as device hd1 at installation
> time had got device hd0 at running time. So the only result of this line
> 62 is to have had grub fail.

The set root command only changes variable. Unless the variable is used
no disk is accessed at all.

> You can see on line 12 of the blkid listing that line 64 would have
> properly set root. You can also see that without lines 62 and 129, I
> would have been able to start the configuration and then run
> grub-mkconfig to adapt grub.cfg at the new configuration.
> So here is the reason why I asked for discontinuing the generation of
> those "set root=" instructions whose only result is to have grub fail.
> As long as I am concerned, I am quite able to suppress those lines by
> myself.

Did you try doing so? The thing is that in that I've just done a test in
VM and setting root in shell to something non-existant and then
executing search works as expected

> The only real issue is to consider whether or not other people
> may act as I do and install a system in a place on a given configuration
> and used it at another place in another configuration.
> Le 19/03/2013 07:50, Vladimir 'φ-coder/phcoder' Serbinenko a écrit :
>> Keep list CC'ed
>> On 18.03.2013 23:50, Arbiel (gmx) wrote:
>>> Hi
>>> Le 14/03/2013 18:59, Vladimir 'φ-coder/phcoder' Serbinenko a écrit :
>>>> On 14.03.2013 16:26, Arbiel (gmx) wrote:
>>>>> Hi
>>>>> The grub installation procedure should make no assumption regarding
>>>>> the
>>>>> eventual runtime configuration concerning device and file references.
>>>>> 1) grub.cfg file contains "set root=.." instructions which refer to
>>>>> partitions which are present at installation time, but could be absent
>>>>> at runtime. These instructions may cause grub to stop booting,
>>>>> displaying a message "No such device", and are of no use as they are
>>>>> followed by "seach --set=root ... " instructions which set root
>>>>> according to the runtime configuration.
>>>>> Please, remove these "set root=.." instructions.
>>>> As long as search has found the right device, the value of root is
>>>> overridden. If it didn't work the problem is somewhere else. The
>>>> usefulness of these lines is for bw-compatibility mainly.
>>> The issue is not with the "search" instructions which, as you say,
>>> overwrite the value set by the preceding "set root=(hd....)"
>>> instructions. The issue is with these "set root=(hd,...) instructions
>>> which can refer to an inexistant device,
>> Not a problem since no file is referenced without explicit drive between
>> these instructions
>>> because the running
>>> configuration is not what the installation configuration was. In that
>>> case, grub displays a "No such device" message and stops the booting
>>> procedure.
>> If you see any such problem, it's caused by a bug somewhere else, not
>> the set root statement. You write a lot about how to fix an issue you
>> haven't even really shown to exist. Please provide a replication
>> instructions with VM and recent bzr checkout
>>>>> 2) grub now embeds a little file to properly set the root variable
>>>>> when
>>>>> core.img and grub/grub.cfg do not reside on the same partition. Such a
>>>>> file should also be embedded even when both core.img and grub/grub.cfg
>>>>> reside on the same partition, as the reference to this partition
>>>>> may get
>>>>> illegal at runtime. No one knows whether or not the destination drive
>>>>> has been ported away to another configuration, where its address
>>>>> differs
>>>>> from what it was at installation time.
>>>> Only the partition number is stored, not the drive. And partition
>>>> number
>>>> doesn't change on disk move
>>>>> Please always embed a file to properly set root, prefix and
>>>>> config_directory.
>>> A recent boot-repair report showed the embedding of a 2 line grub shell
>>> file to properly set the root variable to a device refered to by its
>>> UUID. However, the inclusion may have been the result of the use
>>> gub-mkimage command inside the installation procedure. So, the issue may
>>> be to be reported to Ubiquity, the software responsible for Ubuntu
>>> distributions installation. So forget about my request.
>> UUIDs are used for cross-disk installation. Partition numbers on
>> single-disk ones. In any case neither changes after swapping disks
>> _______________________________________________
>> Bug-grub mailing list
>> address@hidden
>> https://lists.gnu.org/mailman/listinfo/bug-grub

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