Hello. In case you're using our 5.x upstream repositories for Debian or Ubuntu, as originally suggested on https://www.knot-resolver.cz/download/ <https://www.knot-resolver.cz/download/> you'll be running into an expired signing key since yesterday.  As we haven't updated in time again, manual action is needed on every machine, I'm afraid. Let's take this as an opportunity to migrate to our newer repositories that should work better.  You may already know them e.g. from version 6.x or Knot DNS.  Setup is described at https://pkg.labs.nic.cz/doc/?project=knot-resolver <https://pkg.labs.nic.cz/doc/?project=knot-resolver> You may want to also uninstall the original helper package by: apt purge knot-resolver-release Thanks for bearing with this inconvenience. --Vladimir