Caution about Unison upgrade from "backports"

[Paul Johnson]

In Fedora, the version of unison is newer than the version in Hardy,
and so those 2 systems could not communicate with each other through
Unison.  All of the other systems that I sync with are Ubuntu Hardy,
so I was able to synchronize with them.

I did some checking and found a new version of unison is available in
Hardy backports.  I upgraded to unison-2.27.57-1~hardy1.

The problem, which I should have anticipated, but did not, was that
the unison database storage format has changed between the Hardy
version and the backport version.  As a result, the archives created
by unison in Hardy (before upgrading) are not compatible with the
archives created after upgrading. After upgrading, unison says "you
have not synchronized these directories before, so we are going to
scan as if this is the first use of unison." or something like that.
IT rescans the directories, and you have some troubles. For example,
if you had intentionally deleted something in one system, it will find
that file is missing, and propose to copy it back over from the other.
 Any little differences in permissions will have to be dealt with.

Here's what one ought to do.  Run unison for all profiles & systems
that still work with the old version before installing the new
version.  If you do that, then when the new unison runs, it will still
say "ah, you have new directories" but it will scan and find they are
the same and you will start on good footing.

-- 
Paul E. Johnson
Professor, Political Science
1541 Lilac Lane, Room 504
University of Kansas