(non-UEFI) package shim-signed 1.32~16.04.1+0.9+1474479173.6c180c6-1ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

[s-sebast]

I was upgrading my OS (14.04 LTS to 16.04 LTS) with an USB key and a message appeared, I don't remember exactly which one. So I restarted my computer and the 16.04 LTS version seemed installed.

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: shim-signed 1.32~16.04.1+0.9+1474479173.6c180c6-1ubuntu1
ProcVersionSignature: Ubuntu 4.10.0-28.32~16.04.2-generic 4.10.17
Uname: Linux 4.10.0-28-generic x86_64
.proc.sys.kernel.moksbstate_disabled: 0
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
BootEFIContents:
 fw
 fwupx64.efi
Date: Wed Aug 2 19:01:31 2017
Df:
 Sys. de fichiers blocs de 1K Utilisé Disponible Uti% Monté sur
 /dev/sda5 182502748 76830604 96378468 45% /
 /dev/sdg1 15405000 2566248 12838752 17% /cdrom
 udev 8177688 0 8177688 0% /dev
 tmpfs 1638656 9544 1629112 1% /run
EFIBootMgr: Error: command ['efibootmgr', '-v'] failed with exit code 2: efibootmgr: EFI variables are not supported on this system.
EFITables:

ErrorMessage: subprocess installed post-installation script returned error exit status 1
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1.1
 apt 1.2.19
SourcePackage: shim-signed
Title: package shim-signed 1.32~16.04.1+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)