[Bug 1421877] Re: boot fails with lvm root device in /dev/mapper not found after update of libc-bin

[Phillip Susi]

Yes, LVM snapshots are not really usable for this purpose; you need
btrfs to do that.  By not really usable I mean it is impractical to have
more than one snapshot, or to have the snapshot live for very long.
Personally I just tar or dump my root fs to back it up then if things go
wrong, just restore it.

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Title:
  boot fails with lvm root device in /dev/mapper not found after update
  of libc-bin

Status in grub2 package in Ubuntu:
  Opinion

Bug description:
  System:  Ubuntu 14.04 64 bits
  I have run a packages update/upgrade with synaptic. (Note that I had proposed-update repo enabled).
  Among other things a new kernel was installed and libc-bin was updated both likely from proposed-update since I didn't see them in my other box which doesn't use this source  (see attached dpkg.log for full list of recently installed packages. The culprit is probably at the end of that list).

  After the upgrade, I rebooted the system.

  I got the initramfs prompt with an error message saying that it gave up waiting for root devive /dev/mapper/sysvg-lvroot1
  I could not find the mapper entry under /dev but I could find /dev/sysvg/lvroot1 and mount it alright from the busybox prompt.

  Tried booting with 2 previous kernels to no avail: same problem with
  root device even though previous kernels worked fine.

  I booted from live usb, chrooted my ubuntu, merged my 10 days old
  sysvg-lvroot1 lvm snapshot, deleted last kernel from /boot (from last
  update)  and forced reinstalled previous kernel. Then I could boot
  alright and I have disabled proposed-update.

  The problem was with all kernels, hence the culprit is likely grub.cfg
  which is updated at each kernel update.  Between my previous snapshots
  and today failed boot something must have changed on my system which
  has resulted in the grub-mkconfig (or whatever tool is called to write
  grub.cfg when kernel is updated) producing a wrong config.

  Here is a filtered (I have removed what I think is irrelevant, the
  full list is in attachment) list of the packages last installed:

  bsdutils libblkid1 libc-bin libmount1 libuuid1 linux-generic linux-
  headers-3.13.0-46 linux-headers-3.13.0-46-generic linux-headers-
  generic linux-image-3.13.0-46-generic linux-image-
  extra-3.13.0-46-generic linux-image-generic linux-libc-dev mount
  ureadahead util-linux uuid-runtime

  I would say that blkid, uuid and mount are suspicious.
  --- 
  ApportVersion: 2.14.1-0ubuntu3.6
  Architecture: amd64
  DistroRelease: Ubuntu 14.04
  InstallationDate: Installed on 2014-03-24 (326 days ago)
  InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140323)
  Package: grub2 (not installed)
  ProcVersionSignature: Ubuntu 3.13.0-45.74-generic 3.13.11-ckt13
  Tags:  trusty
  Uname: Linux 3.13.0-45-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups:
   
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