[Bug 1065196] Re: update-grub sets wrong kernel root for linux dual boot systems

[Daniel Lago]

It also affects me, using Ubuntu server with other 10 GNU/Linux OSes.

Its a very dark long shot, but I think that the problem can maybe be in
/etc/grub.d/10_linux file, the LINUX_ROOT_DEVICE var behavior is to
being set only on first time (the second time and forward it appears do
not change).

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Title:
  update-grub sets wrong kernel root for linux dual boot systems

Status in “grub2” package in Ubuntu:
  Confirmed

Bug description:
  Installing two versions of linux to separate partitions confuses
  "update-grub". It detects the two linux operating systems and creates
  two menu entries , but it generates a grub.cfg file that makes both
  kernels point their root directory to the same partition.

  Steps to reproduce:

  1. Create three partitions on your hard disk:
  - /dev/sda1: boot partition (mount point: /boot in both linuxes)
  - /dev/sda2: root partition of first linux OS (e.g., Ubuntu precise)
  - /dev/sda3: root partition of alternative linux OS (e.g., for beta testing -- that's what I am trying to do)

  2. Boot into your first linux OS

  3. execute "sudo update-grub"
  update grub detects both linuxes:
  - linux on /dev/sda2 (e.g., precise)
  - linux on /dev/sda3 (e.g., quantal beta)
  it generates grub.cfg which is stored to the shared boot partition, /dev/sda1

  4. open /boot/grub/grub.cfg. Observe that the UUIDs for the kernel
  root partitions are identical on both entries! They both point to
  /dev/sda2, i.e., the partition update-grub was called from.

  To clarify things, this is how the generated grub.cfg looks in
  principle:

  [...]
  menuentry '<name of first linux OS (on /dev/sda2)>' [...] {
          [...]
          set root='(hd0,msdos1)'                # <- this is the boot partition, /dev/sda1
          search --no-floppy --fs-uuid --set=root <UUID of /dev/sda1>
          linux   /vmlinuz-x.x.x root=UUID=<UUID of /dev/sda2> [...]
          initrd [....]
  }
  menuentry '<name of second linux OS (on /dev/sda3)>' [...] {
          [...]
          set root='(hd0,msdos1)'                # <- this is the boot partition, /dev/sda1
          search --no-floppy --fs-uuid --set=root <UUID-of-/dev/sda1>
          linux   /vmlinuz-y.y.y root=UUID=<UUID of /dev/sda2 (!!!)> [...]
          initrd [....]
  }
  [...]

  Note that the "linux" line in the second entry is wrong: it points the
  kernel's root directory to /dev/sda2, but it should point to
  /dev/sda3.

  Essentially this means that both entries will boot the same OS, i.e.,
  the first linux on /dev/sda2. The only difference is that the two
  entries will be running different kernels on the same OS.
  Specifically, none of the entries will really boot the second OS on
  /dev/sda3.

  ProblemType: Bug
  DistroRelease: Ubuntu 12.04
  Package: grub (not installed)
  ProcVersionSignature: Ubuntu 3.2.0-31.50-generic 3.2.28
  Uname: Linux 3.2.0-31-generic x86_64
  NonfreeKernelModules: nvidia
  ApportVersion: 2.0.1-0ubuntu13
  Architecture: amd64
  Date: Wed Oct 10 18:31:38 2012
  EcryptfsInUse: Yes
  InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
  SourcePackage: grub
  UpgradeStatus: Upgraded to precise on 2012-04-28 (165 days ago)

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