On Tue, 02 Jun 2020 17:43:58 +0100, Richard Kettlewell
 wrote:

> 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’.

I agree, but strace might not be the easiest solution.
I use something like:
 rsync --rsh="ssh -o IdentitiesOnly=yes -o IdentityAgent=none -i $KEYFILE"
to customize the way rsync uses ssh.

It's worth a try to use --rsh="ssh -vvv" to get insight in what happens to ssh.

--
Regards,
Kees Nuyt

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