Active Directory Linux

Zentyal Upgrade: Signatures couldn’t be verified because the public key is not available: NO_PUBKEY

A few day ago when I was upgrading some of my servers, I notice that Zentyal was showing as being up to date in the dashboard, but there was also an alert in the dashboard that said that the server was missing an security update. When I logged into it over SSH and tried to manually install updated, I encountered the following error message.