[Bug 1899372] Re: update-grub 10_linux_zfs fails when /usr is a separate filesystem

[Shayne Underwood]

I have resolved the issue in my case. This is a server and besides
Ubuntu I also have TrueNAS installed to another disk as a backup to get
to my files if for some reason I can't get in. What I have discovered is
that anytime the disk containing TrueNAS is connected the GRUB scripts
for ZFS take a dump and leave the "/etc/grub.d/10_linux_zfs: 404: .:
cannot open /tmp/zfsmnt.dCD7rF/etc/os-release: No such file " error. I
initially thought that maybe grub-customizer had botched it so I backed
up my home and reinstalled the OS leaving out grub-customizer and
manually editing my GRUB. I was having a black screen GRUB issue before
enabling console mode and when I updated GRUB I noticed the script took
a dump again so I thought to eject the disk with TrueNAS and try to
update GRUB again so I'm not left in an unbootable state and it solved
the issue. So now I have just disabled the port for my TrueNAS backup
inside the BIOS and all seems well. The reason that rpool was missing in
the grub.cfg is because it was adding the entries under linux instead of
linux_zfs scripts. If anybody else has this issue pay attention to the
scripts in /etc/grub.d/ to find out where your entries are being
generated and disable or remove any other ZFS / Solaris type disks that
may be conflicting. Other than that I'm not sure how else to leave the
TrueNAS drive enabled and not have GRUB take a dump but in my case it is
no big deal considering it is just a backup OS that I can leave
disabled.

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https://bugs.launchpad.net/bugs/1899372

Title:
  update-grub 10_linux_zfs fails when /usr is a separate filesystem

Status in grub2 package in Ubuntu:
  Incomplete
Status in grubzfs-testsuite package in Ubuntu:
  Confirmed

Bug description:
  Description:    Ubuntu 20.04.1 LTS
  Release:        20.04
  grub-common: 2.04-1ubuntu26.4

  I expect grub-update to create grub.cfg with Linux entries for ZFS.
  Instead I am left with an empty list and an unbootable OS.

  The output from update-grub:
  Sourcing file `/etc/default/grub'
  Sourcing file `/etc/default/grub.d/init-select.cfg'
  Sourcing file `/etc/default/grub.d/kdump-tools.cfg'
  Generating grub configuration file ...
  /etc/grub.d/10_linux_zfs: 404: .: Can't open /tmp/zfsmnt.stGSQC/etc/os-release
  Found memtest86+ image: /memtest86+.elf
  Found memtest86+ image: /memtest86+.bin
  done

  This is failing because I have a separate ZFS filesystem for /usr.
  The 10_linux_zfs script is gathering information from /etc/os-release
  which is a symlink to ../usr/lib/os-release.

  The first issue I see in 10_linux_zfs is under function get_dataset_info() at line 382:
  mount -o noatime,zfsutil -t zfs "${base_dataset}" "${mntdir}"

  Since /usr is under a separate filesystem, the symlink would be broken
  and the script fails.  This should mount /usr as well if it is a
  separate filesystem.

  The next issue I see is when the script iterates the zsys snapshots at line 514:
  for snapshot_dataset in $(zfs list -H -o name -t snapshot "${dataset}"); do
      boot_list="${boot_list}$(get_dataset_info ${snapshot_dataset} ${mntdir})\n"
  done

  You would get a similar error message about os-release.
  /etc/grub.d/10_linux_zfs: 410: .: Can't open /.zfs/snapshot/autozsys_oiimb5/etc/os-release

  Again, the script should consider reading the /usr snapshot as well if
  it is a separate filesystem.

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