A testing PPA Usage sudo apt-key adv --fetch-keys https://rkraats.github.io/ppa/KEY.gpg sudo apt update sudo apt install linuxptp Sources https://assafmo.github.io/2019/05/02/ppa-repo-hosted-on-github.html https://pmateusz.github.io/linux/2017/06/30/linux-secure-apt-repository.html