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=== MySQL - The following signatures couldn't be verified because the public key is not available - NO PUBKEY - Ubuntu 20.04 ===

Ошибка при обновлении базы пакетов связанная с MySQL репозиторием:
 # apt update
 W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://repo.mysql.com/apt/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B7B3B788A8D3785C
 W: Failed to fetch http://repo.mysql.com/apt/ubuntu/dists/focal/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B7B3B788A8D3785C
 W: Some index files failed to download. They have been ignored, or old ones used instead.

Решение - это добавить ключи GPG для репозитория MySQL:
 # apt-key adv --keyserver keyserver.ubuntu.com --recv-keys B7B3B788A8D3785C
 # apt update
 # apt upgrade -y