apt update でエラーを吐いた
$ sudo apt update
Hit:1 https://deb.debian.org/debian buster InRelease
Hit:2 https://deb.debian.org/debian-security buster/updates InRelease
Hit:3 https://packages.cloud.google.com/apt cloud-sdk InRelease
Ign:4 https://storage.googleapis.com/cros-packages/84 buster InRelease
Hit:6 https://storage.googleapis.com/cros-packages/84 buster Release
Get:5 https://packagecloud.io/headmelted/codebuilds/debian stretch InRelease [23.4 kB]
Err:5 https://packagecloud.io/headmelted/codebuilds/debian stretch InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0CC3FD642696BFC8
Reading package lists... Done
W: GPG error: https://packagecloud.io/headmelted/codebuilds/debian stretch InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0CC3FD642696BFC8
E: The repository 'https://packagecloud.io/headmelted/codebuilds/debian stretch InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
エラーを見た感じ、証明書の検証が原因のよう
だから、以下のように証明書を追加する
$ sudo apt-get -qO - https://packagecloud.io/headmelted/codebuilds/gpgkey | sudo apt-key add -
OK
証明書管理は、apt-key コマンドで行う
$ apt-key help
Usage: apt-key [--keyring file] [command] [arguments]
Manage apt's list of trusted keys
apt-key add <file> - add the key contained in <file> ('-' for stdin)
apt-key del <keyid> - remove the key <keyid>
apt-key export <keyid> - output the key <keyid>
apt-key exportall - output all trusted keys
apt-key update - update keys using the keyring package
apt-key net-update - update keys using the network
apt-key list - list keys
apt-key finger - list fingerprints
apt-key adv - pass advanced options to gpg (download key)
If no specific keyring file is given the command applies to all keyring files.