[Bug 1835909] Re: grub-probe fails to recognize ext4 partition

[Francis Ginther]

** Tags added: id-5d23848a34b3ca885e55156f

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Title:
  grub-probe fails to recognize ext4 partition

Status in grub2 package in Ubuntu:
  New

Bug description:
  On a recent Bionic Azure image, the command

      grub-probe --device /dev/sda1 --target=fs_uuid

  fails with

      grub-probe: error: not a directory.

  The reason for this seems to be that grub-probe finds the minixfs
  superblock magic 0x138F at offset

      00000410  8f 13 3a 00 00 00 00 00  02 00 00 00 02 00 00 00
  |..:.............|

  then assumes it has found a minixfs-formatted partition and exits with
  an error when it cannot access it, instead of trying other filesystems
  first.

  I don't know what the ext filesystem has stored at that position, and
  whether it is straight-forward to fabricate this manually.

  To reproduce this, you may launch the Azure Bionic image with urn

      Canonical:UbuntuServer:18.04-LTS:18.04.201906271

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