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List:       grub-help
Subject:    Re: grub2 fails to detect partitions if it was installed into file
From:       Pascal Hambourg <pascal () plouf ! fr ! eu ! org>
Date:       2018-07-18 22:02:28
Message-ID: 4e0bf252-4bb5-e0ce-c556-a4cce8e6a959 () plouf ! fr ! eu ! org
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Le 18/07/2018 à 13:20, Sergey Naumov a écrit  :
> 
> I just had to use "losetup --partscan" instead of mounting the main
> partition manually, as with my method there is no information about
> partition size. Anyway, thanks a lot for part_msdos, it helped!

Using losetup -o like you did previously, the loop device end was the 
end of the whole image file instead of the end of the partition. You 
should have set the right size in losetup with the option --sizelimit or 
in mkfs.ext4. Otherwise the filesystem extended to the end of the image 
file, beyond the partition boundaries.

Regarding the need to force inclusion of part_msdos in the GRUB core 
image, it seems that grub-install does not detect that loop0p1 is a 
partition of loop0, so it does not consider that this driver is useful.

> 2018-07-18 12:26 GMT+03:00 Sergey Naumov <sknaumov@gmail.com>:
> 
>> Thanks, Pascal, that helped a bit.
>>
>> But now there is another problem:
>> error: attempt to read or write outside of partition.
>>
>> So grub see partition and its content, it can even load some modules from
>> (hd0,msdos1)/boot/grub/i386-pc.
>>
>> But when I'm trying to load some other modules, like "normal", I see this
>> error:
>> grub rescue> ls
>> (hd0) (hd0,msdos2) (hd0,msdos1)
>> grub rescue> ls (hd0,msdos1)/boot/grub
>> ./ ../ gfxblacklist.txt unicode.pf2 i386-pc/ locale/ fonts/ grubenv
>> grub.cfg
>> grub rescue> set root=(hd0,msdos1)
>> grub rescue> set prefix=(hd0,msdos1)/boot/grub
>> grub rescue> insmod normal
>> error: attempt to read or write outside of partition.
>>
>> What is also interesting, if I use --modules=part_msdos,ext2 instead of
>> --modules=part_msdos, then grub tries to load a system, but neither
>> succeeds nor emits rescue shell - it just hangs.
>>
>> As to your question - I used "losetup -o 1M -f image.img" to create loop
>> device that I can format with mkfs.ext4.
>>
>> Thanks,
>> Sergey.
>>
>>
>> 2018-07-17 21:12 GMT+03:00 Pascal Hambourg <pascal@plouf.fr.eu.org>:
>>
>>> Hello,
>>>
>>> Le 17/07/2018 à 18:09, Sergey Naumov a écrit :
>>>
>>>>
>>>> I'm trying to prepare an image that I can dd into disk or boot using PXE,
>>>> so I install basic system + kernel + grub-pc into directory, then create
>>>> an
>>>> image file, partition it using sfdisk, mount main partiton (ext4), copy
>>>> content of the rootfs into it, and then run grub-install and update-grub
>>>> under chroot.
>>>>
>>>> Everything seems OK, grub.cfg detected kernel and initramfs installed
>>>> into
>>>> created image, but when I try to boot this image either on real system or
>>>> using kvm, grub2 can't find device partitions. What could be a reason of
>>>> it?
>>>>
>>>> I posted the question with more detailed explanation here:
>>>> https://serverfault.com/questions/922319/grub2-fails-to-dete
>>>> ct-partitions-if-it-was-installed-into-file
>>>>
>>>
>>> You really could have copied all the relevant information in your post to
>>> the list, so subscribers do not have to fetch them on the web.
>>>
>>> How did you make the ext4 partition in the image appear as a block device
>>> so that it can be mounted ?
>>>
>>> AFAIK, GRUB looking for the filesystem containing /boot/grub by UUID
>>> means that grub-install believes that it is on a different drive from the
>>> boot+core image. So maybe grub-install did not care to embed the MSDOS
>>> partition table driver into the core image. You can try to force it with
>>>
>>> grub-install --modules=part_msdos <other parameters>
>>>
>>
>>
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