It is very straight forward to upgrade Ubuntu between releases.The BonsaiFramework recommends that with Servers, staying with LTS versions of Ubuntu and upgrading only when the next LTS version is introduced.
Carefully review the differences in releases. You will often find that most new features are GUI related and do not provide any value to the Server environment.
In this example the server is running 9.10 and at the time, the next available long term support release was at the time is 10.04.
If we were behind multiple releases, for example at 9.04, we would first upgrade to 9.10 and then 10.04 by repeating the upgrade instructions.
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