ssh sbwait indfinite timeout on SMP machines

Robert Watson rwatson at
Thu Feb 24 14:30:37 GMT 2005

On Thu, 24 Feb 2005, Dental-on-line wrote:

> We are using two SMP machines (Dell 1750) with 5.3_p2 RELENG and have
> timeout problems with SSH.
> This problem happens ONLY on SMP machines not uniprocessor ones. 

Could you try the following things:

- Boot the box with the debug.mpsafenet=0 tunable set in loader.conf and
  see if the problem recurs?

- Update to 5-STABLE and try with and without debug.mpsafenet=0?  A number
  of TCP locking changes have been made there, and one may help.

Does it happen for every SSH session, or only some? 


Robert N M Watson

> This problem is reproductible using the following steps:
> Connect to the host and when asked for the password type Ctrl-C. On a 
> uniprocessor machine you will have a CLOSE-WAIT timeout that timeouts 
> :-) after one or two minutes. Not so on an SMP machine, the CLOSE-WAIT 
> state lasts forever.
> The problem is if you have more than 10 sessions that fail in the same 
> situation your host ssh daemon is no more usable and you must kill it.
> Thanks,
> Cyril Elkaim
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