Problem: Upgrade to 4.3-1 fails with a GPG Key Error

repository
apt
problem

#1

Problem

The upgrade to UCS 4.3-1 fails and you see messages like this in the file /var/log/univention/updater.log:

W: GPG-Fehler: https://updates.software-univention.de/3.2/maintained/component transition/all/ Release: Die folgenden Signaturen waren ungültig: EXPKEYSIG 1DD67AFB2CBDA4B0 Univention Corporate Server 3.x Archive Key <packages@univention.de>

Solution

Disable the outdated repository and clean local cached data:

ucr set repository/online/component/transition=disabled
apt clean
apt update

#2