On Mon, 8 Oct 2007 14:01:32 +0100 Denys Vlasenko <[email protected]> wrote: > On Sunday 07 October 2007 17:47, Malte Schröder wrote: > > Hello, > > I am encountering some strange data corruption when transferring > > data from one of my PCs that I use as a file-server. > > > > on the server: > > FILE=<large file>; | cut -d" " -f1 | nc -lp5000 -q0; while nc > > -lp5000 -q0 < $FILE; do : ; done > > $ cat z > FILE=z; | cut -d" " -f1 | nc -lp5000 -q0; while nc -lp5000 -q0 < $FILE; do : ; done Sorry, there is a copy'n'paste error in my post, correct line would be: FILE=z ; sha1sum $FILE | cut -d" " -f1 | nc -lp5000 -q0; while nc -lp5000 -q0 < $FILE; do : ;done > > $ sh z > z: line 1: syntax error near unexpected token `|' > z: line 1: `FILE=z; | cut -d" " -f1 | nc -lp5000 -q0; while nc -lp5000 -q0 < $FILE; do : ; done' > > > on the client: > > H=<server>; SUM=$(nc -q0 $H 5000);sleep 1s; while nc -q0 $H 5000 | > > sha1sum | (grep -v $SUM || echo -n .); do sleep 1s ;done > > > > (output looks somewhat like this: > > ..............6dd5fb1ce29d270acdfbb02d00921bf75d141773 - > > ... > > ) > > > > I would expect the sha1sum to be the same in every pass (assuming the > > source file does not change). But every few passes (with no apparent > > pattern) there is a different sum returned. I first noticed this when > > transferring large files (backups) with with SMB and NFS(v3 and v4) but > > to rule that out I tried netcat in the way noted above. > > Does it happen over loopback? I just tried a few times and yes, it also happens on loopback, but much less frequently. Now I am really confused ... > > tcpdump / tcpflow may help seeing whether there is some corruption > (TCP checksumming should have catched that, but worth looking into). > Basically, you wait for "wrong" checksum to appear, then > you stop script and look into tcpdump/tcpflow logs. > -- > vda >
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