How to Ubuntu Update and Dist Upgrade | Ubuntu 19.10
Ubuntu 20.04 LTS (Focal Fossa) -- Full sources.list · GitHub Ubuntu 20.04 LTS (Focal Fossa) -- Full sources.list - sources.list Ubuntu Sources List Generator - Simply Linux Sources List Generator for Ubuntu, Xubuntu, Kubuntu, Edubuntu, Ubuntu Server and other Ubuntu-based distros. It features the official Canonical one repositories as well as other 3rd party repos. Ubuntu Sources List Generator
See an example of what scripts the Community is using to install the UniFi Network Controller on Ubuntu 16.04 and 18.04 in this Community post. (Method A) Install the following trusted key into /etc/apt/trusted.gpg.d
Jul 20, 2020 · Version: Supported Packages: Start of ESM # of Years: End of Life: Ubuntu 18.04 ESM: To be announced : April 2023 : 5 years : April 2028 : Ubuntu 16.04 ESM: To be announced : April 2021 Apr 30, 2020 · Ubuntu uses the apt package manager to install, update, upgrade and remove packages. Apt stores a list of repositories or software channels in the file. File Location and Name: /etc/apt/sources.list and in any file with the suffix.list under the directory
Ubuntu Software will then check your software sources for new updates. Most repositories provide a signing key to be able to verify downloaded packages. So in addition to the steps above, you should follow possible instructions on how to download and install the signing key (GPG key).
Ubuntu Manpage: sources.list - List of configured APT data