Understanding Linux repositories and its setup for troubleshooting

To view and configure the repositories on an Ubuntu device, you can follow these steps:

Viewing the Configured Repositories

The repositories configured in an Ubuntu system are typically listed in the `/etc/apt/sources.list` file and in any files within the `/etc/apt/sources.list.d/` directory.

1.View the main sources list file:

   Open a terminal and run:

   cat /etc/apt/sources.list

2. We can also verify the below as well to check if there is any additional repo link

 ls /etc/apt/sources.list.d/

On the test device, I could not find any additional repo url configured

Setting the Repositories to Default

If you want to reset your repositories to the default configuration, you can replace the contents of `/etc/apt/sources.list` with the default repository configuration for your specific version of Ubuntu. Here is how you can do it:

sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup (below screenshot shows the backed-up)

2. Replace the sources list with default repositories:

   Edit the sources list file with a text editor. You can use `nano`

   sudo nano /etc/apt/sources.list

Replace its contents with the default repositories. Below are the default repositories for Ubuntu 20.04 LTS (Focal Fossa) as an example:

   deb http://archive.ubuntu.com/ubuntu focal main restricted

   deb http://archive.ubuntu.com/ubuntu focal-updates main restricted

   deb http://archive.ubuntu.com/ubuntu focal universe

   deb http://archive.ubuntu.com/ubuntu focal-updates universe

   deb http://archive.ubuntu.com/ubuntu focal multiverse

   deb http://archive.ubuntu.com/ubuntu focal-updates multiverse

   deb http://archive.ubuntu.com/ubuntu focal-backports main restricted universe multiverse

   deb http://security.ubuntu.com/ubuntu focal-security main restricted

   deb http://security.ubuntu.com/ubuntu focal-security universe

   deb http://security.ubuntu.com/ubuntu focal-security multiverse

3. Save and exit the editor.

4. Update the package list:

   Finally, update the package list to apply the changes:

   sudo apt update

apt list –upgradable – provides more information on which are the packages that can be updated to which version