[Bug 1800722] Re: EFI booting + /boot on LVM == inaccessible boot menu

[Launchpad Bug Tracker]

This bug was fixed in the package grub2 - 2.02-2ubuntu8.10

---------------
grub2 (2.02-2ubuntu8.10) bionic; urgency=medium

  [ Mathieu Trudel-Lapierre ]
  * debian/grub-check-signatures: check kernel signatures against keys known
    in firmware, in case a kernel is signed but not using a key that will pass
    validation, such as when using kernels coming from a PPA. (LP: #1789918)
  * debian/patches/mkconfig_leave_breadcrumbs.patch: make sure grub-mkconfig
    leaves a trace of what files were sourced to help generate the config
    we're building. (LP: #1812863)

  [ Steve Langasek ]
  * debian/patches/quick-boot-lvm.patch: If we don't have writable
    grubenv and we're on EFI, always show the menu.  Closes LP: #1800722.

 -- Mathieu Trudel-Lapierre <cyphermox at ubuntu.com>  Wed, 09 Jan 2019
14:04:09 -0500

** Changed in: grub2 (Ubuntu Bionic)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1800722

Title:
  EFI booting + /boot on LVM == inaccessible boot menu

Status in grub2 package in Ubuntu:
  Fix Released
Status in grub2 source package in Bionic:
  Fix Released
Status in grub2 source package in Cosmic:
  Fix Released

Bug description:
  [Impact]
  This issue makes it impossible for UEFI users to access to boot menu and choose their kernel if /boot is installed on LVM.

  [Test case]
  1) Install Ubuntu on UEFI; put /boot on a LVM LV.
  2) Reboot after the install
  3) Verify that you will get a GRUB menu at boot.

  [Regression potential]
  Give particular attention to boot behavior on different disk setups: failure to show the menu on LVM or other disk setups when holding the SHIFT key, or showing the menu at every boot unnecessarily on other types of disk configurations: /boot on a physical partition, etc.

  ---

  Because EFI does not support instantaneous read of modifier keys (i.e.
  holding down shift at boot), the only way to reliably show a boot menu
  is by letting the system boot, interrupting the boot, and letting the
  menu be displayed because 'recordfail' has been set.

  If /boot/grub is on LVM, recordfail does not work, because grub
  doesn't have write support on LVM, so saveenv doesn't work.  Indeed,
  from the grub.cfg on such a system, the recordfail function is written
  as:

  function recordfail {
    set recordfail=1
    # GRUB lacks write support for lvm, so recordfail support is disabled.
  }

  The interaction of these two limitations means that systems with
  /boot/grub on LVM cannot reliably get a grub menu, ever.

  While I think that in the long term we should always put /boot/grub on
  the ESP (which means it will always be writable by grub), which is in
  fact what we did for Ubuntu Core, in the meantime I believe what we
  need to do here is always show the boot menu if we are booted under
  EFI and we have a non-writable grubenv.

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