til/system/deleting-a-repository-that-is-not-needed.md

Say you added a repository with sudo add-apt-repository -y ppa:... and you want to delete it maybe because it gives you an error while you are trying to update your system:

E: The repository 'http://ppa.launchpad.net/...' 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.

You will need to find corresponding file in sources.list.d and delete it.

cd /etc/apt/sources.list.d
sudo rm bad-repo.list