If you have, for whatever reason, destroyed your local /etc/apt/sources.list file which Ubuntu uses for packages updates, here is a useful site which can regenerate it:

https://repogen.simplylinux.ch/

My recommendation is to enter

  • country
  • release (get it with “lsb_release -a” command)
  • tick the first 12 checkboxes

Copy the result to your local file and run “apt-get update”.

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