Some Repo Public Key Missing

Ubuntu

Example:

Text Only

Err:6 https://apt.releases.hashicorp.com focal InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AA16FCBCA621E701

Fix:

Bash

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys AA16FCBCA621E701