Re: Unison 2.9.20 and OpenSSH-4.1p1-2: hangs as server.

[Andrew Schulman <andrex at alumni dot utexas dot net>]

> after just a few bytes of network traffic (far 
> less than the full 400kb), it hangs.  Runs of "ps -ef" confirm that the 
> unison-2.9.20 processes are still running on both machines, but there is 
> no network traffic, and no CPU usage.
> 
> Attempts to run Unison on directories with lots of changed files, such 
> that Unison has multiple connections running, crash at the same point 
> with uncaught exceptions or "broken pipe" errors instead of hanging.  (I 
> can reproduce those if they'd be useful, but they seemed just random and 
> cryptic, and they weren't consistent if I changed the files, so I didn't 
> save them.)

Brooks, I do remember seeing a lot of reports about 6 months or so
ago, that Unison was hanging.  My recollection is dim but I think it
had to do with some bad combination of versions of cygwin.dll and
Unison.  Are you using the latest cygwin.dll on your servers?

Invoking unison with -debug will provide a lot of output, which may or
may not be useful.  At least you can see what was the last thing
Unison was doing before it hung, and that may ring a bell somewhere.
Also, exceptions and broken pipes are obvious errors that may lead
more easily to a solution if you report the details.

On balance though, I recommend that you upgrade to a recent (or at
least more recent) version of Unison if you can.  2.9.20 is getting
pretty old now.  It's still provided in Cygwin in order to allow
maximum version compatibility with other hosts, but there are a ton of
bug fixes and many new features in later versions.

Several more recent versions of Unison are available in Cygwin.  On
FreeBSD I don't know, but even if you have to fetch and build a more
recent version yourself, this is usually easy as long as you have
OCaml installed.  Of course all of your hosts have to be running the
same version of Unison, since different versions won't talk to each
other; or with versions 2.13.x and later, only the first two version
numbers (e.g. 2.13) have to match.

Good luck,
Andrew.


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