[Bug 1893454] [NEW] lvm misdetected: as root=dm-2; should be dm-0 or rhel7-root

[Mustafa Kocaturk]

Public bug reported:

This is a problem that requires editing the grub.cfg after every update
as follows:

diff -r1.2 /boot/grub/grub.cfg
320c320
< 	linux /vmlinuz-0-rescue-094290ad3c25419d9b671b141b6ea616 root=/dev/dm-0
---
> 	linux /vmlinuz-0-rescue-094290ad3c25419d9b671b141b6ea616 root=/dev/dm-2
333c333
< 		linux /vmlinuz-0-rescue-094290ad3c25419d9b671b141b6ea616 root=/dev/dm-0
---
> 		linux /vmlinuz-0-rescue-094290ad3c25419d9b671b141b6ea616 root=/dev/dm-2
345c345
< 		linux /vmlinuz-3.10.0-862.3.2.el7.x86_64 root=/dev/dm-0
---
> 		linux /vmlinuz-3.10.0-862.3.2.el7.x86_64 root=/dev/dm-2

The target kernel expects to find the root filesystem on dm-0, also known as rhel_smt2-root, not on dm-2.
However, Ubuntu kernel numbers the dm-* devices differently, as follows:

mu at mu-HP-Z620-Workstation:~/Desktop Fri Aug 28 11:39:11 1 1 $ sudo dmsetup ls
200828_113958
rhel_smt2-swap	(253:4)
rhel_smt2-root	(253:2)
vgubuntu-root	(253:0)
vgubuntu-swap_1	(253:1)
rhel_smt2-home	(253:3)
mu at mu-HP-Z620-Workstation:~/Desktop Fri Aug 28 11:39:58 1 0 $ ls -l /dev/dm-*
200828_114013
brw-rw---- 1 root disk 253, 0 Aug 28 10:30 /dev/dm-0
brw-rw---- 1 root disk 253, 1 Aug 28 10:30 /dev/dm-1
brw-rw---- 1 root disk 253, 2 Aug 28 10:30 /dev/dm-2
brw-rw---- 1 root disk 253, 3 Aug 28 10:30 /dev/dm-3
brw-rw---- 1 root disk 253, 4 Aug 28 10:30 /dev/dm-4

That is, the dm- minor device numbering differs.

Symptom: The boot menuentry breaks whenever os-update is called,
practically after every new kernel update, and rhel7 becomes unbootable.

Suggested workaround: Use the OS-defined name, rhel_smt2-root, instead
of dm-2 in the root= parameter. Reverse lookup of minor device number in
the first table gives the OS name.

** Affects: os-prober (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1893454

Title:
  lvm misdetected: as root=dm-2; should be dm-0 or rhel7-root

Status in os-prober package in Ubuntu:
  New

Bug description:
  This is a problem that requires editing the grub.cfg after every
  update as follows:

  diff -r1.2 /boot/grub/grub.cfg
  320c320
  < 	linux /vmlinuz-0-rescue-094290ad3c25419d9b671b141b6ea616 root=/dev/dm-0
  ---
  > 	linux /vmlinuz-0-rescue-094290ad3c25419d9b671b141b6ea616 root=/dev/dm-2
  333c333
  < 		linux /vmlinuz-0-rescue-094290ad3c25419d9b671b141b6ea616 root=/dev/dm-0
  ---
  > 		linux /vmlinuz-0-rescue-094290ad3c25419d9b671b141b6ea616 root=/dev/dm-2
  345c345
  < 		linux /vmlinuz-3.10.0-862.3.2.el7.x86_64 root=/dev/dm-0
  ---
  > 		linux /vmlinuz-3.10.0-862.3.2.el7.x86_64 root=/dev/dm-2

  The target kernel expects to find the root filesystem on dm-0, also known as rhel_smt2-root, not on dm-2.
  However, Ubuntu kernel numbers the dm-* devices differently, as follows:

  mu at mu-HP-Z620-Workstation:~/Desktop Fri Aug 28 11:39:11 1 1 $ sudo dmsetup ls
  200828_113958
  rhel_smt2-swap	(253:4)
  rhel_smt2-root	(253:2)
  vgubuntu-root	(253:0)
  vgubuntu-swap_1	(253:1)
  rhel_smt2-home	(253:3)
  mu at mu-HP-Z620-Workstation:~/Desktop Fri Aug 28 11:39:58 1 0 $ ls -l /dev/dm-*
  200828_114013
  brw-rw---- 1 root disk 253, 0 Aug 28 10:30 /dev/dm-0
  brw-rw---- 1 root disk 253, 1 Aug 28 10:30 /dev/dm-1
  brw-rw---- 1 root disk 253, 2 Aug 28 10:30 /dev/dm-2
  brw-rw---- 1 root disk 253, 3 Aug 28 10:30 /dev/dm-3
  brw-rw---- 1 root disk 253, 4 Aug 28 10:30 /dev/dm-4

  That is, the dm- minor device numbering differs.

  Symptom: The boot menuentry breaks whenever os-update is called,
  practically after every new kernel update, and rhel7 becomes
  unbootable.

  Suggested workaround: Use the OS-defined name, rhel_smt2-root, instead
  of dm-2 in the root= parameter. Reverse lookup of minor device number
  in the first table gives the OS name.

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