Following the instructions from the OwnCloud Desktop client download page, I got the following error trying to install the owncloud-client package:
[SOLUTION]WARNING: The following packages cannot be authenticated!
libqt5keychain1 libowncloudsync0 owncloud-client-l10n owncloud-client
Install these packages without verification? [y/N] n
E: Some packages could not be authenticated
Thanks to a comment posted by FlorianFranzen, I found a fix.
The issue was that apt didn't properly load its sources, because it already had the Release file loaded before and didn't recognize a change.
Therefore, remove (=comment out) the OwnCloud repository line in /etc/apt/sources.list.d/owncloud-client.list:
Code: Select all
deb http://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/ /