Olá. Eu tive esse problema quando eu executar o comando apt-get update recebo o seguinte adicionado ao final do mesmo:
rr:15 http://ppa.launchpad.net/gnome3-team/gnome3/ubuntu artful Release
404 Not Found
Hit:16 https://dl.yarnpkg.com/debian stable InRelease
Reading package lists... Done
E: The repository 'cdrom://Ubuntu 17.10 _Artful Aardvark_ - Release amd64 (20171018) artful Release' does not have a Release file.
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.
E: The repository 'http://ppa.launchpad.net/gnome3-team/gnome3/ubuntu artful Release' does not have a Release file.
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.