Hey,
the traceback shows this error happens not for files you already have installed, but for scripts that are downloaded from the Univention update servers during the upgrade. These scripts are supposed to verify certain conditions are met prior to the upgrade. They also upgrade certain packages first before the rest in order to ensure the upgrade doesn’t run into known dependency problems.
In your case it’s likely the 4.2 pre-upgrade script for which this happens.
The downloaded scripts are then stored in a temporary directory beneath /tmp, made executable and then executed. Something seems to go wrong with that process.
You can try to enable debugging messages for the updater. Unfortunately this cannot be done simply through a UCR variable, it seems. So please edit the following file in a text editor: /usr/share/univention-updater/univention-updater Look for def main(). In that function you should find a call to ud.init(LOGNAME, 0, 0). Directly after this call insert the following lines:
ud.set_level(ud.NETWORK, ud.ALL)
ud.set_level(ud.PROCESS, ud.ALL)
Make sure that the lines are indented exactly as deep as the existing call to ud.init as depth of indentation is relevant in Python.
Then re-run the updater. The /var/log/updater.log should now contain a lot more messages about trying to retrieve files and trying to run scripts. Please post that output here.
m.