Comment 5 for bug 1971036

In older versions of Ubuntu, I believe multiple "unison-VERSION" packages were provided, and the "unison-all" metapackage simply installed all of them for you. In both Ubuntu 20.04.5 and 22.04.1, those version-specific Unison packages seem to be long gone, and only ONE version of Unison is provided. Thus the unison-all package was already effectively useless on 20.04.5, but at some point in the past, it was very useful indeed!

Why were the version-specific Unison binary packages discontinued? They were very useful and user-friendly.

Ubuntu 20.04.5 LTS provides "/usr/bin/unison-2.48.4" from its "unison" package. I tried copying the 20.04.5 /usr/bin/unison-2.48.4 into /usr/local/bin/ on my 22.04.1 machine. Then I specified "servercmd = unison-2.48.4" in my Profile file. This does NOT work, as Unison reports:

Fatal error
Server: Archive file seems damaged (input_value: ill-formed message): throw away archives on both machines and try again

On Ubuntu 20.04.5 (focal), simply copying the old /usr/bin/unison-* binaries from older versions of Ubuntu often worked fine, they would run on 20.04 and work for syncing with older versions of Ubuntu. That apparently no longer works with 22.04.1 (jammy) vs. 20.04.5 (focal).