[PLUG] ssh problem...

Larry Brigman larry.brigman at gmail.com
Thu Jul 3 17:21:23 UTC 2008


On Thu, Jul 3, 2008 at 9:34 AM, chris (fool) mccraw <gently at gmail.com> wrote:
> On 7/2/08, robinson-west user <plug_1 at robinson-west.com> wrote:
>
>>     Another symptom of the problem is that an ssh session to this
>>  machine will often times lock up when I run a command like cat on a
>>  large file.  The wired equivalent that would cause this would be
>>  unplugging the network line.  Tried pinging to test the link,
>>  0% packet loss even if I ping 200 times.  Well, ls can lock the
>>  session up also.  In a couple of days, I'll up the onboard ram
>>  by a factor of 4.
>>
>>      I guess the question is, how do I get more information about
>>  this problem?
>
> same way you debug any other problem of unknown origin and nature:
> try to isolate the failure case.
>
> since you have something that will trigger it, try seeing if you can
> find the exact length of output that will trigger it every time, and
> if removing one byte will always save you--is the problem consistent?
> try making the file you cat contain different characters--are all
> spaces ok?  maybe it's a control character that hangs up the
> connection.  does using ssh with -v to connect give you any more
> information during the disconnection?  do any other connection types
> (telnet, web) also hang?
>
> this is sounding to me more and more like corrupted network packets,
> which could come from bad cabling, cards, ram, switch (if any), cable
> location (someone once told me that running net cables alongside power
> cables would lead to interference).  does moving the machines to be
> physically adjacent, directly corrected with a different cable, help
> at all?
This is especially true if you are not running the correct cable type
for the network speed of the link.

>
> i'd also fire up tcpdump and see if there's anything obvious about the
> failing packets--especially if you can reproduce the failure exactly
> with something that's not ssh so you can read the plaintext contents
> and see if any bits are flipped.
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