Adrian  writes:
> Adrian  writes
>>>Are you familiar with strace? At this point that’s definitely the tool
>>>I’d reach for.
>>>
>>>  [1] https://tools.ietf.org/html/rfc4253#section-11.1
>>>
>>
>>I've heard of it, but I haven't (yet) had a reason to use it.
>>
>
> Following another failure overnight, I've tried strace.
>
[....]

You need to trace the ssh processes, on both hosts, not (just)
rsync. Locally you could use ‘strace -tt -f’ to follow trace subprocesses
as
well. Remotely the easiest way is probably to attach the trace after
things have started, with ‘strace -f -tt -p PID’.

Attaching after things start means we don’t quite get the complete
picture but since we’re looking for hints as to why things stop (or not)
that may not matter.

(-tt asks for timestamps, which makes it easier to match up events
across the two hosts, assuming they both have correctly set clocks.)

--
https://www.greenend.org.uk/rjk/

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