Re: GRUB only offers a rescue shell

[jmh6]

Hi Pascal,

    Further experiments to try to clone my working Knoppix 6.4.3 hard 
drive.

    The layout is /dev/sda1 - swap /dev/sda2 - OS.

    I used fdisk to get hard disk layout more or less the same using 
another Linux to mount the 'new' harddrive and the working OS image as a 
USB memory stick.

    I dd copied the working image /dev/sda2 to what is eventually to be 
/dev/sda2. It is /dev/sdb2 on the cloning system. It seems to have copied 
OK. I can mount it, etc.

    I tried to use grub-install. I was expecting it to ask me a bunch of 
questions and finally install a good grub including MBR on /dev/sdb. Grub 
would not do that. Or at least I could not figure out how to do it. There 
were no known good grub examples that I found.

    So I took the known good MBR from the running system and dd copied it 
to the 'new' hard drive.

    On boot I see 'GRUB ' on the CRT and then dead. So I assume grub 
'must' be loading some absolute block number from the hard drive of 
assembly code , but doesn't load the right block(s). It would be MOST 
helpful to know exactly what grub was trying to do at this point?? I 
probably could then have just patched the MBR assembly code and have been 
up and running?

    Next attempt. Use CD to install a new version of Knoppix 6.4.3 on the 
'new' hard drive. Worked all OK. Boots OK. So somehow it told Grub and 
friends what to do?? It would be VERY nice to have whatever was done 
really documented.

    As I write this I am using dd to replace the recently install 
/dev/sda2 with the known working /dev/sda2. Maybe grub will 'know' what to 
do. Or maybe things will just happen to be in the right place for grub to 
work??

    If this fails. And I expect it may. The next step is to image copy the 
whole known working /dev/sda image. MBR, swap space, and working image as 
one large image and see if that works? Later I can probably use fdisk to 
make the unused hard disk available as some sort of partition?

    It would be VERY nice to have an easy way to clone a working Linux to 
a new hard drive or memory stick.

    Of course I should write it :).

    Thanks in advance for your time and help,
    John


On Fri, 14 Jul 2017, Pascal Hambourg wrote:

> Le 14/07/2017 ? 06:15, Jordan Uggla a ?crit :
> > On Thu, Jul 13, 2017 at 1:20 PM, Pascal Hambourg <address@hidden> 
> wrote:
> > > Or one could force grub-install to include the part_msdos module in the 
> core
> > > image with the --modules=part_msdos option.
> >
> > One could, and it would work, but basically only by chance due to how
> > cross disk installs are supported in grub. grub-install would still
> > see it as a cross disk install, and would still set it up as such.
> > Because cross disk installs use an embedded config that searches by
> > UUID, and that search happens to still search partitions even when
> > grub-install "knew" that $prefix was not to be found on a partition,
>
> IMO it is a pity that GRUB does not also search by UUID even when the 
> core image and $prefix are on the same disk. It would avoid boot failure 
> when the partition containing $prefix is renumbered (logical partition 
> numbers are not stable when you create or remove another logical partition).
>
> > $prefix would be configured properly but it's an ugly work around that
> > could break if grub's implementation changes. I am firmly of the
> > opinion that the --modules option should never be used, as it is
> > almost exclusively misused and it is easy to break things when using
> > it.
>
> I had to use --modules once on a regular setup because grub-install did 
> not include some required module by itself.
>
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