package grub-pc 2.04-1ubuntu26.4 failed to install/upgrade: installed grub-pc package post-installation script subprocess returned error exit status 1

[Stanislav Sokolov]

Upgrade from 18.04. After this error the upgrade halted and the machine needed to be restarted with a live USB stick (as it would not boot into the semi-upgraded system), I then chrooted into the system and followed the instructions here https://ostechnix.com/how-to-fix-broken-ubuntu-os-without-reinstalling-it/ to be able to boot into 20.04

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: grub-pc 2.04-1ubuntu26.4
ProcVersionSignature: Ubuntu 5.4.0-48.52-generic 5.4.60
Uname: Linux 5.4.0-48-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.9
Architecture: amd64
CasperMD5CheckResult: skip
Date: Mon Oct 12 23:03:35 2020
DuplicateSignature:
 package:grub-pc:2.04-1ubuntu26.4
 Setting up grub-pc (2.04-1ubuntu26.4) ...
 dpkg: error processing package grub-pc (--configure):
  installed grub-pc package post-installation script subprocess returned error exit status 1
ErrorMessage: installed grub-pc package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2019-07-07 (463 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-48-generic root=UUID=75277517-eb28-4f84-b3cb-8ab29620ed1c ro quiet splash vt.handoff=7
Python3Details: /usr/bin/python3.8, Python 3.8.5, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: /usr/bin/python2.7, Python 2.7.18, python-is-python2, 2.7.17-4
RelatedPackageVersions:
 dpkg 1.19.7ubuntu3
 apt 2.0.2ubuntu0.1
SourcePackage: grub2
Title: package grub-pc 2.04-1ubuntu26.4 failed to install/upgrade: installed grub-pc package post-installation script subprocess returned error exit status 1
UpgradeStatus: Upgraded to focal on 2020-10-12 (0 days ago)

[Julian Andres Klode (juliank)]

Thanks for your bug report. We believe this is a duplicate of bug 1896608.