Ubuntu End of Life and Upgrades
https://mreschke.com/254/ubuntu-end-of-life-and-upgrades
<p>This topic helps with two things. One is to upgrade an old Ubuntu release to a new release, and by old I mean one that is no longer supported. Keep in mind that if say 9.04 is unsupported, but 9.10 is still supported, you can simply do the <tt>do-release-update</tt>. This doc helps when both 9.04 and 9.10 and above are EOL (end of life). Second is to maintain the use of an old Ubuntu distro even after its repositories stop working. Basically if you don't install the LTS (Long Term Support) release of Ubuntu then your distro is only supported for about a year. After that year all your repositories (using apt-get) fail and cannot be found. <strong>This is because Ubuntu archives the old repositories to a different URL.</strong> You don't actually have to upgrade your old Ubuntu distro, and you can continue to use it and its repos, you just have to switch to the new repo URL's. See below.</p>