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I'm trying to use netcat to catch kernel printing (netconsole) using nc -l -u -p 6666.

But when I use this utility in Ubuntu, it immediately exits.

Trying to figure out why, I see that in the manual page it is described that -l & -p can't be used together.

The next time I tried to execute it as following.

This time I started to get some reply but then it exits.

$ nc -l -u 6666
netconsole: local port 6665
netconsole: local IP 0.0.0.0
netconsole: interface 'eth0'
netconsole: remote port 6666
netconsole: remote IP 10.0.0.1
netconsole: remote ethernet address ff:ff:ff:ff:ff:ff
netconsole: local IP 10.0.0.2

Then I get back host prompt, as if netcat existed without printing anything more.

Can someone help me figure out what I'm doing wrong ?

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2 Answers 2

up vote 0 down vote accepted

@ransh, you're using OpenBSD Netcat, which has a different syntax. I suggest you to change to netcat-traditional:

sudo update-alternatives -config nc

Select the option /bin/nc.traditional. Verify and new version:

nc -h
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You can use -l and -p yes. Try:

sudo nc -u -v -l -p 6666

Use -u if you're looking for UDP packages.

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Hi Wiliiam, I just tried it now in ubuntu 10.04 but I get the description of nc arguments (as if it contain some error argument). I copy pase exactly what you wrote above. Note that in manual page it is said not to use -l & - together. –  ransh Aug 5 at 17:56
    
So strange. I tested my command before post the answer. I'm using Debian Wheezy. Can you update your nc package? Can you verify your nc version, please? –  Willian Paixao Aug 5 at 18:01
    
I updated it now, but still it is the same result. How can I get the version ? –  ransh Aug 5 at 18:05
    
from man page: -l Used to specify that nc should listen for an incoming connection rather than initiate a connection to a remote host. It is an error to use this option in conjunction with the -p, -s, or -z options. Additionally, any timeouts specified with the -w option are ignored. –  ransh Aug 5 at 18:05
    
The version is written in the very first line of help output: nc -h. –  Willian Paixao Aug 5 at 18:15

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