ssh/scp sometimes unable to connect

Ryan Johnson ryan.johnson@cs.utoronto.ca
Fri Jan 20 15:51:00 GMT 2012


On 20/01/2012 8:31 AM, Corinna Vinschen wrote:
> On Jan 19 16:31, Ryan Johnson wrote:
>> Hi all, I just re-ran setup.exe yesterday and now ssh behaves 
>> erratically, often timing out instead of asking for a password:
>>> $ ssh cs.utoroto.ca ssh: connect to host cs.utoroto.ca port 22: 
>>> Connection timed out 
>> I rebased my system after the update and replaced the 13 Nov snapshot 
>> I've been using with the one from 11 Jan, but the problem persists. 
>> This doesn't seem to be fork-related in any obvious way: ssh runs but 
>> then times out on an fcntl syscall (see attached strace.out). 
>> Normally I'd blame the network or the host, but sysadmins for the 
>> machine are unaware of anything that might cause the problem; I can 
>> maintain an open ssh connection to that host (cpu and memory usage 
>> there are both low) and can connect to it from other terminals 
>> windows during the failing attempt, which suggests the problem is on 
>> my side of the network. Even more strangely, changing things (ssh 
>> instead of scp, different user name, different host alias) makes it 
>> work or not (and, of course, sometimes it just works). Running strace 
>> or not doesn't seem to make a difference, though. 
> There's nothing weird in the strace. Your connect call gets a WinSock 
> error 10060, WSAETIMEDOUT, that's all. There were no changes to the 
> connect call since May 2011. At this point, not even the new OpenSSL 
> 0.9.8t should be involved.
Grr. I tried to send a reply yesterday, but apparently the list bounced 
it due to mime type text/html (why , Thunderbird, why???).

It was PEBCAK -- typing 'utoroto.ca' rather than 'utoronto.ca' -- 
compounded by the fact that ssh apparently reports DNS failures as if 
they were merely connection timeouts.

Sorry for the false alarm.
Ryan


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