[CentOS] ssh_exchange_identification: Connection closed by remote host

Stephen Harris lists at spuddy.org
Sat Sep 15 09:01:38 EDT 2012


On Sat, Sep 15, 2012 at 07:01:03AM +0200, M. Fioretti wrote:
> 
> On Fri, September 14, 2012 11:48 pm, Stephen Harris wrote:
> 
> > 1) What happens if you run "telnet yourhost 22".
> 
> this is what happens (with the proper IP of course):
> 
> >      Trying 1.2.3.4...
> >      Connected to yourhost (1.2.3.4)
> >      Escape character is '^]'.
> >      Connection closed by foreign host.

This is important; it means the remote SSH server never says 'hello'.

> > 2) How quickly does the "closed" occur?
> 
> I'd say 4/5 seconds

This is possibly indicative of resource starvation at the remote end;
the connection is going into the listen queue, then being accepted but
the process then fails.  It might mean "out of memory" (for example)
so the server can't fork() the new sshd process.  If you mean "4 or 5s"
then we might also be seeing swapping delays.

There _are_ other reasons for this type of behaviour (eg firewalls, network)
but that's the most common one that I've seen.

> #####################################################
> [marco at avalon ~]$ ssh -v -p xxx me at example.com

I assume the "xxx" here matches the port you tested with the telnet
test.  Otherwise the telnet test is useless.

-- 

rgds
Stephen


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