package unattended-upgrades 0.90ubuntu0.9 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

[Flavio del Valle Aldasoro]

failed to upload proprietary packages during installation

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: unattended-upgrades 0.90ubuntu0.9
ProcVersionSignature: Ubuntu 4.4.0-139.165-generic 4.4.160
Uname: Linux 4.4.0-139-generic i686
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: i386
Date: Sat Nov 3 11:17:28 2018
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationDate: Installed on 2015-12-01 (1067 days ago)
InstallationMedia: Xubuntu 14.04.3 LTS "Trusty Tahr" - Beta i386 (20150805)
PackageArchitecture: all
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1.5
 apt 1.2.29
SourcePackage: unattended-upgrades
Title: package unattended-upgrades 0.90ubuntu0.9 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: Upgraded to xenial on 2018-11-03 (0 days ago)

[Balint Reczey (rbalint)]

The bug here is that debconf can't connect to the X server to ask the user about replacing u-u's configuration file.
While this is not a bug in unattended-upgrades, u-u 1.8 will include a fix to avoid triggering the debconf question when the configuration file is intact:
https://github.com/mvo5/unattended-upgrades/pull/152