在 ubuntu 下 apt update 顯示 error message:
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 467B942D3A79BD29 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 467B942D3A79BD29 W: Some index files failed to download. They have been ignored, or old ones used instead.
這個問題，重開機還是會一直遇到，每次下 apt update 就會顯示。解法是服用下面的指令，還有每一台電腦顯示的 key 會不一樣，要修改為你的環境裡遇顯示的 key 值。
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 467B942D3A79BD29
詳解：
https://itsfoss.com/solve-gpg-error-signatures-verified-ubuntu/
GPG error: The following signatures couldn’t be verified
The error tells you that your system cannot identify a certain GPG public key (PUBKEY). What you need to do is to fetch this public key in the system.