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Inexplicable EOF
Hi All,

I'm seeing something which I would not believe could happen had I not
seen it for myself.  It's intermittent and thus not easily repeatable.

On client, I ran: "ssh -i cert -x -T -oBatchMode=yes example.com
batchjob" and ssh exited cleanly, immediately, and displaying no
output.  When I saw it, I repeated the command, with the same results, a
few times.

On example.com, cert.pub is installed in .ssh/authorized_keys. Batchjob
is executable and in PATH, and starts (after #! /bin/sh) with "echo
"`date`: $0 $*" >> /tmp/log".  Nothing appeared /tmp/log for those
occassions when client's ssh exited cleanly, immediately and without
displaying output.  Nothing appeared in /var/log/syslog to indicate that
something was awry.

The one clue that I can think of, if it is a clue, is that I have two
DNS A records published for example.com, one for the primary instance
and the other for a hot-backup.  Both are virtual servers hosted on
different Linux servers.  The primary is running and the hot-backup is
not.  DRBD is used to keep the hot-backup synchronised with the
primary.  The idea is that I can switch server roles without needing to
reconfigure client.  My experience is that openssh tries all A records
in sequence until it connects and that this is a viable strategy.

I feel that openssh would print something if it was unable to get a
connection, and, that having got a connection, example.com would print
something to /tmp/log.  For ssh to cleanly exit with nothing output and
nothing logged stumps me.

Example.com is x64 architecture running Ubuntu 16.04.5.  It's reasonably
up-to-date except for openssh-server, which is 1:7.2p2-4ubuntu2.4.

Client is Raspberry Pi 3B+ running Raspbian 9.4.  Openssh-client is
1:7.4p1-10+deb9u3.

Both machines have plenty of free memory.

It's uncommon for me to reach out for ideas, but I'm reaching out now. 
Any ideas?

Thanks in advance.

David

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Re: Inexplicable EOF [ In reply to ]
Use "ssh -vvv ..." for more debugging output, or even "strace -fttTs200 ssh ..." for a local trace; if that doesn't help, I suggest strace on the server side as well.
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