If you get an error message like this $ sudo apt update ... Err:2 https://apt.releases.hashicorp.com focal InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AA16FCBCA621E701 ... W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://apt.releases.hashicorp.com focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AA16FCBCA621E701 W: Failed to fetch https://apt.releases.hashicorp.com/dists/focal/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AA16FCBCA621E701 you have to install the new gpg public key according to the official installation instructions: https://www.hashicorp.com/official-packaging-guide In my case (Ubuntu 20.04) this did work: wget -O- https://apt.releases.hashicorp.com/gpg | gpg --dearmor | sudo tee /usr/share/keyrings/hashicorp-archive-keyring.gpg I don't know how to verify for sure (100 %) if this new key is not compromised (eg. by a hacked web site) since there is no other reliable channel to find the expected fingerprint (hints welcome :-)