[Bug 1848797] Re: After upgrading to 19.10, boot screen shows: "Error: symbol 'grub_file_filters' not found."

[Telman Asadov]

*** This bug is a duplicate of bug 1891680 ***
    https://bugs.launchpad.net/bugs/1891680

Because of Bionic 18.04 EOL (https://ubuntu.com/blog/ubuntu-18-04-eol-
for-devices) this issue with "Error: symbol 'grub_file_filters' not
found." become actual this days.

In my experience, in Azure VM after upgrading process to 20.04 it may fail.
Reason for that, boot mode (UEFI Mode or legacy BIOS mode). It's very important point.

If your previous machine in Generation 1 and you upgrade to 20.04 LTS, it switch to UEFI boot mode.
And as documented in (https://learn.microsoft.com/en-us/troubleshoot/azure/virtual-machines/chroot-environment-linux) at 3rd point, it's important create Rescue VM in same generation and make rescue operations to switch back to Legacy BIOS mode.

Generation 1 Ubuntu 20.04 come with UEFI mode, but Generation 2 Ubuntu 20.04 come with legacy mode.
So, If your previous machine was in Generation 1, create Rescue Linux VM in in Generation 1, and do operation as #31 @Ronzo described.

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https://bugs.launchpad.net/bugs/1848797

Title:
  After upgrading to 19.10, boot screen shows: "Error: symbol
  'grub_file_filters' not found."

Status in grub2 package in Ubuntu:
  Confirmed
Status in grub2 source package in Eoan:
  Confirmed

Bug description:
  After upgrading to 19.10 the boot screen shows the following error:

  Error: symbol 'grub_file_filters' not found.
  Entering rescue mode...

  I could fix it after i booted Ubuntu 19.10 live and used the chroot
  repair method as described here
  https://wiki.ubuntuusers.de/GRUB_2/Reparatur/#chroot-Methode (german)

  Workaround
  ----------
  From https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1848797/comments/18
  "In any case, right now the best thing to do to repair is to boot from a Live image (USB or CD-ROM), and follow the steps in https://help.ubuntu.com/community/Grub2/Installing#via_ChRoot to repair GRUB by hand, or reinstall."

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