Eric on 10 Jul 2006 14:01:52 -0000


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[PLUG] perplexing file transfer problem


I've encountered a file transfer problem that is quite perplexing - 
and I'm at a loss to identify the cause.  Part of the problem is 
that it's random and it's complex (a number of variables are 
involved) and therefore hard to narrow down to a single failure
point.

The basic scenario is this: I have a shell script that uses curl 
commands to retrieve multiple files from two ftp servers.  The 
host for this is a rented box that I do not have root or physical 
access to.  I do not have root or physical access to the ftp 
server either for that matter... I'm just a user/developer 
tryin' to bring the data home :-)

The script ran on a shared box for several months but was moved to 
it's own box with a new IP on Thursday.  On Friday the random 
failures began.. some initial portion of the file would download at 
normal speed then the rate would drop to zero bytes per second and 
stay there.  If the script is re-run it may download that file just 
fine only to fail on the next download.  Also, the size of the 
initial download appears random too - one was 292 kB, the next was 1.9 
Meg... etc.  There is a log fragment at the bottom of this email 
showing the relevant part (the output of the curl command).  

Other factors I've considered:

   The transfer randomly fails if we use ftp from the command line too
     - it's not just curl

   For security reasons, the ftp server must have the IP of the 
      requestor on file - and it does.  Otherwise, we could not 
      even log it.

   The failure can be from either of the ftp servers - although they
      are on the same domain they are separate host names.

Now if anybody has seen something similar or has any ideas on how to 
further troubleshoot this I'd be very grateful.  Keep in mind that it's
been working like clockwork since March or April so it's not the 
programmer's fault :-D

Thanks.
Eric

Our host:

# uname -a
Linux host.xxxxxxxxx.com 2.6.9-34.EL #1 Wed Mar 8 00:07:35 CST 2006 
  i686 athlon i386 GNU/Linux

Log fragment showing how it fails:

-----
curl -n $DATAURL1 > $DATAFILE1
 retrieving BR_20060710_013000__dat_full_.zip
 % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
 0 24.1M    0  1460    0     0   1283      0  5:29:00  0:00:01  5:28:59  1283
 0 24.1M    0  168k    0     0   106k      0  0:03:53  0:00:01  0:03:52  371k
 2 24.1M    2  684k    0     0   264k      0  0:01:33  0:00:02  0:01:31  470k
 4 24.1M    4 1166k    0     0   319k      0  0:01:17  0:00:03  0:01:14  462k
 4 24.1M    4 1199k    0     0   219k      0  0:01:52  0:00:05  0:01:47  277k
 4 24.1M    4 1199k    0     0   185k      0  0:02:13  0:00:06  0:02:07  225k
 4 24.1M    4 1199k    0     0   160k      0  0:02:33  0:00:07  0:02:26  175k
 4 24.1M    4 1199k    0     0   141k      0  0:02:54  0:00:08  0:02:46 89742
 4 24.1M    4 1199k    0     0   126k      0  0:03:15  0:00:09  0:03:06  5781
 4 24.1M    4 1199k    0     0   114k      0  0:03:35  0:00:10  0:03:25     0
 4 24.1M    4 1199k    0     0   104k      0  0:03:56  0:00:11  0:03:45     0
 4 24.1M    4 1199k    0     0  98511      0  0:04:17  0:00:12  0:04:05     0
 4 24.1M    4 1199k    0     0  91188      0  0:04:37  0:00:13  0:04:24     0
 4 24.1M    4 1199k    0     0  84879      0  0:04:58  0:00:14  0:04:44     0
 .
 .   [five hours later we see.... Current Speed is stuck at zero]
 .
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:03:55 99:56:12     0
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:03:56 99:56:11     0
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:03:57 99:56:10     0
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:03:58 99:56:09     0
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:03:59 99:56:08     0
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:04:00 99:56:07     0
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:04:01 99:56:06     0
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:04:02 99:56:05     0
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:04:03 99:56:04     0
 4 24.1M    4 1199k    0     0     67      0   4d 09h  5:04:04 99:56:03     0



-- 
------------------------------------------------------------------------
#  Eric A Lucas
#  ------------
#   "Oh, I have slipped the surly bond of earth
#    and danced the skies on laughter-silvered wings... 
#        -- John Gillespie Magee Jr.
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