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Old 02-04-2010, 03:44 AM   #1
Frank85
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tcp_probe doesn't work - need help


Hello,

I'm using ubuntu 9.10 with kernel 2.6.33.
I want to plot the cwnd of some tcp connections over the time.

So I activate the module (as root) with:
modprobe tcp_probe
and after that I did:
cat /proc/net/tcpprobe > test.log &

And than I do a little bit surfing or other things, which use tcp - but the file test.log is empty.

Has somebody an idea or an suggestion?

Regards
Frank
 
Old 02-06-2010, 10:17 PM   #2
noden
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I dont really know what cwnd is but here is a wild guess.

Doesnt cat /proc/net/tcpprobe > test.log & exit emediately after execution? Within a second or so? While tcpprobe is still empty?
Shouldnt you loop that command or use something else?
Or maybe use >> instead of > to append instead of replace so the usefull content is not overwritten with "nothing"?
Maybe you could use the tail command instead of cat?

I dont know. I hope it is somewhat usefull.
 
Old 02-08-2010, 02:54 AM   #3
Frank85
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Quote:
Originally Posted by noden View Post
I dont really know what cwnd is but here is a wild guess.

Doesnt cat /proc/net/tcpprobe > test.log & exit emediately after execution? Within a second or so? While tcpprobe is still empty?
No, cat will be still running in background. I did a test and after the test I kill the process. The test duration is different from 1s to 30-60s.
The problem is, I don't know why it is empty, that's my problem.

Quote:
Originally Posted by noden View Post
Shouldnt you loop that command or use something else?
Or maybe use >> instead of > to append instead of replace so the usefull content is not overwritten with "nothing"?
Maybe you could use the tail command instead of cat?

I dont know. I hope it is somewhat usefull.
The tail command doesn't work. My command is correct! append ">>" changes nothing.
 
Old 02-08-2010, 06:39 AM   #4
gratuitous_arp
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The cat command you used will not continually write new changes to a file, as noden pointed out.

The tailf command, or tail -f is probably the easiest way to do what you want.

Code:
(tail)> touch logfile.log
(tail)> tail -f logfile.log >> changes.txt &
(tail)> cat changes.txt 
(tail)> echo new line >> logfile.log 
(tail)> cat changes.txt 
new line
(tail)> cat logfile.log 
new line
 
Old 02-10-2010, 01:12 AM   #5
Frank85
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Quote:
Originally Posted by gratuitous_arp View Post
The cat command you used will not continually write new changes to a file, as noden pointed out.

The tailf command, or tail -f is probably the easiest way to do what you want.
I know, what you say. But if it is not continually I have at least one line in the file or not?
But my file is empty.
I tried the tail -f /proc/net/tcpprobe but I never see only one line, if I make TCP connections.

So need another idea...

Regards
 
Old 02-15-2010, 08:24 AM   #6
gratuitous_arp
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I see what you're trying to do now. There seems to be some reliability issues with tcpprobe. I would try tcpdump instead.
 
Old 02-16-2010, 01:50 AM   #7
Frank85
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Quote:
Originally Posted by gratuitous_arp View Post
I would try tcpdump instead.
The problem is, that tcpdump doesn't log the local cwnd value, which I want to plot.
Tcpdump analyzes only the packages not the local buffer.

So your hint with tcpdump doesn't help me.
 
  


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