[Bug 1926528] Re: random failure of grub-installer, working after several retries

[christopheg]

For those using preseed and having the same problem, a workaround is to
fix grub-installer in partman/early_command.

The following line in preseed.cfg will do the trick:

d-i partman/early_command string \
  sed -i "s/initial_proc_contents=\"$(ls $ROOT/proc)\".*/set +e ; & ; set -e/" /usr/bin/grub-installer ;

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https://bugs.launchpad.net/bugs/1926528

Title:
  random failure of grub-installer, working after several retries

Status in grub-installer:
  New
Status in grub-installer package in Ubuntu:
  New

Bug description:
  I prepared an unattended install usb key for focal base on netboot.iso
  "http://archive.ubuntu.com/ubuntu/dists/focal/main/installer-amd64/current/legacy-images/netboot/mini.iso"

  I'm modifying it to install a preseed to create user account, auto
  partitioning and such things.

  On some machines the unattended install stops when executing the step
  "Install the GRUB boot loader on a hard disk".

  The problem was rather bizarre because if I retried to execute several
  times the Install Grub step it eventually worked.

  As the installation logs were not saying much, I eventually edited
  grub-installer on the boot key to enable the commented 'set +x' at the
  beginning of the script.

  Is the content the content of syslog relevant to this bug, both for a
  breaking boot loader installation and a working one.

  I was able to dig out and find where the bug is coming from. Actually
  the origin of the bug is rather funny.

  grub-installer script enables break on error with a 'set -e' at
  beginning of the script.

  A few lines below the script do:

     initial_proc_contents="$(ls $ROOT/proc)"

  But in the failing cases ls command is returning an exit code of 1
  instead of 0 and stops the script.

  I checked by doing a direct ls /target/proc ; echo $? from the shell.
  And I actually get 1 most of the time and eventually 0 when I get
  lucky (which would lead to grub installing correctly). My
  understanding of that the underlying cause is that some process
  terminated while ls was running and thus the pid of that process
  disappeard from the /proc directory in the middle of the command.

  After find that I was also able to check the bug disappears when
  modifying grub-installer (just did 'set +e' just before the ls and
  reenabled 'set -e' just after it, but there may be a better way to fix
  that).

  After that change the grub installation step works every time and if I
  remove that change it starts again to break randomly.

  Hopefully this report will help to fix that behavior in grub-installer
  as I don't know how to prepackage package it in my key.

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