I'm using Ubuntu 20.04.3 LTS x86_64 and I've been trying to install the newest version of the kernel using:

sudo apt update && sudo apt upgrade

But by the end of the run it always shows the following message:

Adding boot menu entry for UEFI Firmware Settings

/etc/grub.d/35_fwupd: line 5: /usr/share/grub: Is a directory

run-parts: /etc/kernel/postinst.d/zz-update-grub exited with return code 126

dpkg: error processing package linux-image-5.4.0-84-generic (--configure):

 installed linux-image-5.4.0-84-generic package post-installation script subprocess returned error exit st

atus 1

Errors were encountered while processing:

 linux-image-5.4.0-84-generic

E: Sub-process /usr/bin/dpkg returned an error code (1)

The output of uname -r is:

5.4.0-81-generic.

That means that the kernel isn't correctly installed.

Does anybody have an idea of what's going on?

Edit:

By request I'm posting the content of my /etc/grub.d/35_fwupd file:

#! /bin/bash

# SPDX-License-Identifier: LGPL-2.1+

set -e



${pkgdatadir:?}

# shellcheck source=/dev/null

. "$pkgdatadir/grub-mkconfig_lib"



if [ -f /var/lib/fwupd/uefi_capsule.conf ] &&

   ls /sys/firmware/efi/efivars/fwupd-*-0abba7dc-e516-4167-bbf5-4d9d1c739416 1>/dev/null 2>&1; then

      source /var/lib/fwupd/uefi_capsule.conf

      if [ "${EFI_PATH}" != "" ] && [ "${ESP}" != "" ]; then

      echo "Adding Linux Firmware Updater entry" >&2

cat << EOF

menuentry 'Linux Firmware Updater' $menuentry_id_option 'fwupd' {

EOF

      ${grub_probe:?}

      prepare_grub_to_access_device '`${grub_probe} --target=device ${ESP}` | sed -e "s/^/	/"'

cat << EOF

    chainloader ${EFI_PATH}

}

EOF

      fi

fi