When I open Ubuntu Software, it shows me that there are some updates which have to be done. But after clicking them for several times, the installation process just doesn't work. I also tried to restart.
If I use the Software Updater it tells me this message:
If I click OK, the update ends. If I click settings all options are checked:
This whole update process was really not user friendly developed. Do you know what can be done else? I also tried the terminal sudo apt update sudo apt upgrade, there are still undone updates in the Software Center and the Software Updater!
The output of the terminal is:
W: GPG error: http://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY
E: The repository 'http://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 Release' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
PS: Who has marked this as duplicate? The so called duplicate is about why is Ubuntu Software showing these updates? Should I install them? My question is about how to install them? I can't install them because it doesnt work!
SOLUTION:
For me the terminal, the software-center etc failed, but Synaptic Package Manger worked! Even if it makes no sense at all, because all these apps do the same thing. I hope Ubuntu could explain this to me.
I'd let go of the GUI first.
Open a terminal, e.g. by pressing
CRTL+ALT+Tand then run