(non-UEFI, 17.04 fresh install) package shim-signed 1.28+0.9+1474479173.6c180c6-1ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

during upgrading of lubuntu 14.10 on my Asus X200CA laptop to lubuntu 17.04, the grub2 installation part failed. however, on restarting the computer, the laptop booted normally, but got this error automatically after booting. not much of an issue for me, but reporting nonetheless.

ProblemType: Package
DistroRelease: Ubuntu 17.04
Package: shim-signed 1.28+0.9+1474479173.6c180c6-1ubuntu1
ProcVersionSignature: Ubuntu 4.10.0-19.21-generic 4.10.8
Uname: Linux 4.10.0-19-generic x86_64
.proc.sys.kernel.moksbstate_disabled: 0
.sys.firmware.efi.efivars.MokSBStateRT-605dab50-e046-4300-abb6-3dd810dd8b23: Error: [Errno 2] No such file or directory: '/sys/firmware/efi/efivars/MokSBStateRT-605dab50-e046-4300-abb6-3dd810dd8b23'
.sys.firmware.efi.efivars.SecureBoot-8be4df61-93ca-11d2-aa0d-00e098032b8c: Error: [Errno 2] No such file or directory: '/sys/firmware/efi/efivars/SecureBoot-8be4df61-93ca-11d2-aa0d-00e098032b8c'
ApportVersion: 2.20.4-0ubuntu4
AptOrdering:
 shim:amd64: Install
 shim-signed:amd64: Install
 NULL: ConfigurePending
Architecture: amd64
BootEFIContents:
 fw
 fwupx64.efi
Date: Tue Apr 18 13:01:02 2017
Df:
 Filesystem 1K-blocks Used Available Use% Mounted on
 /dev/sda1 151755932 97539348 46484720 68% /
 /dev/sdb1 7545436 1982304 5563132 27% /cdrom
 udev 914884 0 914884 0% /dev
 tmpfs 186192 8192 178000 5% /run
EFIBootMgr: Error: command ['efibootmgr', '-v'] failed with exit code 2: EFI variables are not supported on this system.
ErrorMessage: subprocess installed post-installation script returned error exit status 1
RelatedPackageVersions:
 dpkg 1.18.10ubuntu2
 apt 1.4
SourcePackage: shim-signed
Title: package shim-signed 1.28+0.9+1474479173.6c180c6-1ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)