[Bug 1876943] Re: package grub-pc 2.04-1ubuntu26 failed to install/upgrade: installed grub-pc package post-installation script subprocess returned error exit status 1

[Douglas E Engert]

Running VirtualBox 6.1 on Windows 10, I cloned Xubuntu 18.04 VM to new ssd and resized the .vhd which ran gparted to move swap are resizing the root partition. Then upgraded to 20.04. This caused all sorts of problems and I followed: https://askubuntu.com/questions/1231849/how-to-fix-update-problems-ubuntu-20-04
to get a running system. 

I got the following before and continue to get it even after following the above URL: 
  "installed grub-pc package post-installation script subprocess returned error exit status 1"
when anything is installed. 

By modiging /var/lib/dpkg/info/grub-pc.postinst:
-- grub-pc.postinst.dee.orig	2020-09-26 14:04:44.012323484 -0500
+++ grub-pc.postinst	2020-09-26 14:05:50.028324633 -0500
@@ -1,6 +1,8 @@
 #!/bin/bash
 set -e
-
+PS4='Line ${LINENO}: '
+set -x
+set -v
 # Apply a sed expression using extended regular expressions in place to a
 # file, if it exists.  The file is the first argument in order to work
 # neatly with apply_conf_tweaks.

Then running:
sudo dpkg --configure -a
The last few lines are:

Line 677: '[' true = false ']'
Line 680: db_input critical grub-pc/install_devices_empty
Line 66: _db_cmd 'INPUT critical' grub-pc/install_devices_empty
Line 42: _db_internal_IFS=' 	
'
Line 43: IFS=' '
Line 44: printf '%s\n' 'INPUT critical grub-pc/install_devices_empty'
Line 47: IFS='
'
Line 48: read -r _db_internal_line
Line 49: IFS=' 	
'
Line 52: RET='30 question skipped'
Line 53: case ${_db_internal_line%%[ 	]*} in
Line 59: return 30
Line 690: exit 1
rm -f /tmp/grub.ekWa3OkQHZ
Line 1: rm -f /tmp/grub.ekWa3OkQHZ
dpkg: error processing package grub-pc (--configure):
 installed grub-pc package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 grub-pc

-----
This shows problem is with "grub-pc/install_devices_empty"

I can provide other debugging info, or test a fix if that would help.

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https://bugs.launchpad.net/bugs/1876943

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

Status in grub2 package in Ubuntu:
  Confirmed

Bug description:
  this happened on first apt-get install upgrade after fresh Ubuntu
  20.04 install from scratch not any update

  
  lsb_release -rd
  Description:	Ubuntu 20.04 LTS
  Release:	20.04

  
  apt-cache policy  grub2
  grub2:
    Installed: (none)
    Candidate: 2.04-1ubuntu26
    Version table:
       2.04-1ubuntu26 500
          500 http://us.archive.ubuntu.com/ubuntu focal/universe amd64 Packages

  
  uname -m && uname -r && cat /etc/*release
  x86_64
  5.4.0-14-generic
  DISTRIB_ID=Ubuntu
  DISTRIB_RELEASE=20.04
  DISTRIB_CODENAME=focal
  DISTRIB_DESCRIPTION="Ubuntu 20.04 LTS"
  NAME="Ubuntu"
  VERSION="20.04 LTS (Focal Fossa)"
  ID=ubuntu
  ID_LIKE=debian
  PRETTY_NAME="Ubuntu 20.04 LTS"
  VERSION_ID="20.04"

  ProblemType: Package
  DistroRelease: Ubuntu 20.04
  Package: grub-pc 2.04-1ubuntu26
  ProcVersionSignature: Ubuntu 5.4.0-14.17-generic 5.4.18
  Uname: Linux 5.4.0-14-generic x86_64
  NonfreeKernelModules: wl
  ApportVersion: 2.20.11-0ubuntu27
  Architecture: amd64
  CasperMD5CheckResult: skip
  Date: Tue May  5 10:28:31 2020
  ErrorMessage: installed grub-pc package post-installation script subprocess returned error exit status 1
  InstallationDate: Installed on 2020-05-05 (0 days ago)
  InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Alpha amd64 (20200309)
  ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-14-generic root=UUID=2a498b8e-c1b0-4cb8-9440-fccd950ec4ff ro quiet splash vt.handoff=7
  Python3Details: /usr/bin/python3.8, Python 3.8.2, python3-minimal, 3.8.2-0ubuntu2
  PythonDetails: N/A
  RelatedPackageVersions:
   dpkg 1.19.7ubuntu3
   apt  2.0.2
  SourcePackage: grub2
  Title: package grub-pc 2.04-1ubuntu26 failed to install/upgrade: installed grub-pc package post-installation script subprocess returned error exit status 1
  UpgradeStatus: No upgrade log present (probably fresh install)

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