[Tfug] scp transfers stalling

[Brian Murphy]

Check the NIC duplex. (ethtool eth0)  This often happens when the switch
is hard set for full duplex and the NIC auto-negotiates at half.

Brian


Quoting John Gruenenfelder <johng at as.arizona.edu>:
> Hello all,
>
> I've got a problem with scp file transfers stalling and never recovering.
> It's happening on only one of three Debian systems I use, though, and I can't
> seem to figure out the cause.
>
> The machine with the problem is running Debian/testing using openssh
> 4.7p1-12.  For the working machines, one is Debian/unstable with 5.1p1-2 and
> the other is Debian/stabe with whatever version of openssh it currently has
> (it has the Debian key-bug fixes, but I can't access it right now).
>
> The stalls seem to occur only in one direction: when I copy data *from* the
> machine to mine over the Internet.  It does not seem to happen when I scp
> files to the machine.  The stalls usually, but not always, occur early in the
> transfer of a particular file.  The stalls are not constant, though.  If you
> repeat your scp command again and again, eventually it will work.  
> Stalls seem
> to happen roughly 50% of the time.  I really wish scp could resume
> transfers...
>
> The main difference between these three machines in their Net connectivity.
> The stalling machine is at the UA and therefore has loads of bandwidth.  For
> the working machines, one is my cable broadband with *very* low upload speed
> (no more than 320 kbit) and the other is on a DakotaCom DSL link with
> reasonable upload speed (still nowhere near UA speeds).
>
> I'm not doing anything tricky with the network or SSH settings; it's all
> pretty standard.  My first thought was that it was the poor router 
> the machine
> plugged into.  There were other problems with it and I was hoping this was
> another one of them.  However, the router has been replaced by a nice WRT54GL
> (though not yet with non-Linksys firmware) and while it fixed the other
> issues, it did not fix the stalling.
>
> It's also not the link from UA to me or the network on my end as this same
> stalling problem is happening to other users connecting from varied networks.
>
> I'm running out of ideas and things to test.  Having scp be more 
> verbose gives
> little extra output and shows nothing useful in regards to this issue.  At
> first the problem seemed to be linked to the Debian key-bug fixes, 
> but further
> checking revealed that it actually began shortly before that problem was
> fixed.
>
> Other protocols seem to have no problems.  For example, if I'm having 
> too much
> trouble with scp, I can just stuff the file into ~/public_html and grab it
> with wget and have no issues at all.
>
> Possibly related to this scp stalling is that my SSH sessions to this machine
> occasionally stop responding and never come back.  They need to be axed with
> the tilde-period combo.  Especially annoying when you're typing an email.
> This problem, though, occurs much less frequently than the scp stalls and
> usually only happens after I've let an SSH session sit idle for a while.
> Perhaps it has something to do with data volume?
>
> Does anybody have ideas as to what might be causing this?  My boss really
> wants some answers and I need to give them to him.  :)
>
>
> --
> --John Gruenenfelder    Research Assistant, UMass Amherst student
>                         Systems Manager, MKS Imaging Technology, LLC.
> Try Weasel Reader for PalmOS  --  http://weaselreader.org
> "This is the most fun I've had without being drenched in the blood
> of my enemies!"
>         --Sam of Sam & Max
>
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The opinions or statements expressed herein are my own and should not be
taken as a position, opinion, or endorsement of the University of
Arizona.