Situation

An error appeared while running sudo apt-get update. The original error message is as follows.

오류:6 https://cli-assets.heroku.com/apt ./ InRelease
  다음 서명들은 공개키가 없기 때문에 인증할 수 없습니다: NO_PUBKEY 0000000000000
받기:5 https://packages.cloudfoundry.org/debian stable InRelease [2,679 B]

Solution

The solution is as follows.

$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys [오류원문의 공개키 복붙]

Cause

-Upon installing Ubuntu and using it for the first time, or running apt-get update for the first time, the process may fail to proceed because of a public key.

What is GPG? It is OpenPGP from GNU Privacy Guard (GnuPG).

It is a tool that provides digital encryption and signing services using the OpenPGP standard. In a public-key system, each user has a key pair consisting of a private key and a public key. A user’s private key is kept secret and therefore never needs to be disclosed. A public key can be given to anyone with whom the user wishes to communicate. In other words, it is a software package used to verify the authenticity of distribution files.

The exact details are not particularly important; simply make the authentication request according to the guide below, and it will be applied without requiring any additional authentication.

Original source) https://oopaque.tistory.com/98