For some time now, I was receiving the following warnings after an otherwise successful run of apt update: plain 1W: http://linux.dropbox.com/ubuntu/dists/disco/Release.gpg: 2Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), 3see the DEPRECATION section in apt-key(8) for details. 4W: http://prerelease.keybase.io/deb/dists/stable/InRelease: 5Key is stored in legacy trusted.