Could not delete variable: Interrupted system call (package shim-signed 1.34.9+13-0ubuntu2 failed to install/upgrade: installed shim-signed package post-installation script subprocess returned error exit status 1)

reported while upgrading from 17.10 to 18.04

ProblemType: Package
DistroRelease: Ubuntu 18.04
Package: shim-signed 1.34.9+13-0ubuntu2
ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
Uname: Linux 4.15.0-20-generic x86_64
.proc.sys.kernel.moksbstate_disabled: Error: [Errno 2] No such file or directory: '/proc/sys/kernel/moksbstate_disabled'
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
Date: Sun May 13 20:39:06 2018
EFITables:
 May 13 20:58:00 satish kernel: efi: EFI v2.40 by INSYDE Corp.
 May 13 20:58:00 satish kernel: efi: ACPI 2.0=0x7887e014 ESRT=0x77f67618 SMBIOS=0x780f5000
 May 13 20:58:00 satish kernel: secureboot: Secure boot could not be determined (mode 0)
 May 13 20:58:00 satish kernel: esrt: Reserving ESRT space from 0x0000000077f67618 to 0x0000000077f67650.
ErrorMessage: installed shim-signed package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2016-05-26 (716 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
Python3Details: /usr/bin/python3.6, Python 3.6.5, python3-minimal, 3.6.5-3
PythonDetails: /root/Error: command ['which', 'python'] failed with exit code 1:, Error: [Errno 2] No such file or directory: "/root/Error: command ['which', 'python'] failed with exit code 1:": "/root/Error: command ['which', 'python'] failed with exit code 1:", unpackaged
RelatedPackageVersions:
 dpkg 1.19.0.5ubuntu2
 apt 1.6.1
SecureBoot: 6 0 0 0 0
SourcePackage: shim-signed
Title: package shim-signed 1.34.9+13-0ubuntu2 failed to install/upgrade: installed shim-signed package post-installation script subprocess returned error exit status 1
UpgradeStatus: Upgraded to bionic on 2018-05-13 (0 days ago)