Canonical 4.x to 6.x upgrade docs?

[Artem Kuchin]

>What's the basis for your suspicion?

My memory might play tricks on me, but i think I remember that i tried to upgrade
from 4.1 to 5.3 longtime ago and it did not work. I had to up to 5.0 and the to 5.3.
But that might be just some weird client install (i did not install freebsd on that box
originally). The world just did not compile. I canot provide any more  detail on that,
sorry.

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Regards,
Artem