apt-get update work, we simply need to edit
/etc/apt/sources.list and update all URLs from
archive.ubuntu.com to point to
old-releases.ubuntu.com, as per the following sed command:
sudo sed -i.bak -r 's/(archive|security).ubuntu.com/old-releases.ubuntu.com/g' /etc/apt/sources.list
sudo apt-get update seems to run without a hitch. Of course if you do this, you’re accepting to use an insecure system, and should do
sudo apt-get install update-manager-core; do-release-upgrade as soon as possible.