Re: Grub installation may get erroneous after a hardware reconfiguration

[Arbiel (gmx)]

Hi

Obviously you are right. The lines which I incriminated do not access 
the drives, and only set the variable. So no matter the device exists or 
not.

I'm just returning from a test after having removed the "set root=" 
lines, and I got the same "no such device" message.

No other explanation then coming from core.img.

I haven't recorded on paper how I exactly installed grub on my external 
device, but a report just produced on my PC by boot-repair indicates :
"Grub2 (v2.00) is installed in the MBR of /dev/sdb and looks at sector 1 
of the same hard drive for core.img. core.img is at this location and 
looks in partition 1 for (,msdos9)/boot/grub."
Even if the phrase "and looks in partition 1" does not seem quite 
correct, the phrase "for (,msdos9)/boot/grub" clearly shows my mistake : 
at installation time I made grub look for another grub.cfg file than the 
one I should have.

How difficult it is to incriminate myself !!

I'm really sorry for the trouble I generated.

Arbiel


Le 19/03/2013 14:56, Vladimir 'φ-coder/phcoder' Serbinenko a écrit :
> 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
> > >
> > >
> > >
> > >
> > > _______________________________________________
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