What is the correct output of cat /etc/apt/sources.list?
Solution 1:
Here is a simple example of a standard /etc/apt/sources.list file for Ubuntu 12.04:
deb http://archive.ubuntu.com/ubuntu precise main universe restricted multiverse
deb http://archive.ubuntu.com/ubuntu precise-updates universe main multiverse restricted
deb http://archive.ubuntu.com/ubuntu precise-backports universe main multiverse restricted
deb http://archive.ubuntu.com/ubuntu precise-security universe main multiverse restricted
The easiest way to edit the sources.list file is from the terminal in nano editor using the following command:
sudo nano /etc/apt/sources.list
The instructions for using nano are always displayed at the bottom of the page. Use the keyboard combination Ctrl + O and after that press Enter to save the file to its current location. Use the keyboard combination Ctrl + X to exit nano.
Make sure to run this command after changing sources.list to refresh the list of available software.
sudo apt update
A standard sources.list file for Ubuntu 16.04 looks like this:
deb http://archive.ubuntu.com/ubuntu/ xenial main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ xenial-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu xenial-security main restricted universe multiverse
deb http://archive.canonical.com/ubuntu xenial partner
A standard sources.list file for Ubuntu 18.04 looks like this:
deb http://archive.ubuntu.com/ubuntu/ bionic main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu bionic-security main restricted universe multiverse
deb http://archive.canonical.com/ubuntu bionic partner
A standard sources.list file for Ubuntu 20.04 looks like this:
deb http://archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu focal-security main restricted universe multiverse
deb http://archive.canonical.com/ubuntu focal partner
Solution 2:
I know it is quite late to answer this question but since (being a newbie), I spent more than 24 hours due to this issue, I found this link quite helpful. It contains all default content for the ubuntu files: https://repogen.simplylinux.ch/
Actually this site takes information from the user about their distro of linux and the names of files they want and then provides the default content of files as output which we can copy and use.