I tried to install a music player called Cantata, and it looks like it is no longer current, now every morning when doing its round of updates I get the message "The repository 'http://ppa.launchpad.net/ubuntuhandbook1/cantata/ubuntu bionic Release' does not have a Release file. W: Updating from such a repository can't be done securely, and is therefore disabled by default." What do I do? What is the command line to remove the repository? Thanks! Fred
Okay, I used this link: https://www.2daygeek.com/how-to-remove-delete-ppas-on-ubuntu-debian-linux-mint-elementary-os/
Method 3 worked fine for me.