[Bug 1897785] Re: 10_linux_zfs: empty bootmenu if POSIXLY_CORRECT

[Jens Elkner]

FWIW: /usr/sbin/grub-probe is also posixly incorrect, e.g.:

# export POSIXLY_CORRECT=1
# /usr/sbin/grub-probe --device /dev/sda2 --target=partmap
/usr/sbin/grub-probe: error: cannot find a GRUB drive for /dev/sda2.  Check your device.map.

# unset POSIXLY_CORRECT
# /usr/sbin/grub-probe --device /dev/sda2 --target=partmap
gpt


So e.g. if one has POSIXLY_CORRECT set, but not GRUB_TERMINAL (the default in /etc/default/grub), /etc/grub.d/00_header assumes gfxterm and therefore indirectly calls /usr/share/grub/grub-mkconfig_lib:prepare_grub_to_access_device() - which in turn fails, because it calls /usr/sbin/grub-probe w/o unsetting POSIXLY_CORRECT before. Since this aborts grub.cfg generation, a disaster recovery is needed on the next reboot if there is not already an old grub.cfg which is able to boot a kernel ... 

If one sets GRUB_TERMINAL=console ,
mkconfig_lib:prepare_grub_to_access_device() doesn't get invoked and
update-grub and in turn grub-mkconfig -o /boot/grub/grub.cfg generates a
valid/usable  config.

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https://bugs.launchpad.net/bugs/1897785

Title:
  10_linux_zfs: empty bootmenu if POSIXLY_CORRECT

Status in grub2 package in Ubuntu:
  Triaged

Bug description:
  If one has POSIXLY_CORRECT env var set (which is the case for all our
  admin/operator accounts) and one calls /usr/sbin/update-grub or grub-
  mkconfig ... it produces a /boot/grub/grub.cfg with a single entry
  'UEFI Firmware Settings' (fwsetup). So the after a reboot the OS is
  not bootable anymore unless one is able to remember, which kernel
  exactly got installed (because Ubuntu does not link the kernel/ram
  image to generic names like vmlinuz , initrd) and which of the dozens
  of hds and partitions actually contain the kernel/ram image to boot.

  The root cause for this is /etc/grub.d/10_linux_zfs and its mount
  usage:

  Since Linux mount requires arguments given in a posixly incorrect
  "order", a script should always unset POSIXLY_CORRECT, when it is
  going to call mount. Otherwise mount errors out, and because the
  script has 'set -e', the script gets aborted immediately.

  NOTE: 'zfs mount ...' also calls 'mount', so same requirement applies
  to 'zfs {mount|create} ...'

  Env:
  Distributor ID:	Ubuntu
  Description:	Ubuntu 20.04.1 LTS
  Release:	20.04
  Codename:	focal

  Linux box 5.4.0-48-generic #52-Ubuntu SMP Thu Sep 10 10:58:49 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
  with latest updates installed.

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