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Port flow capture

 
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Homework and Emergencies Emergency UNIX and Linux Support Port flow capture
# 1  
Port flow capture

I am trying to get an output using the command
Code:
 tcpdump -w /tmp/syn.pcap 'tcp[tcpflags] & (tcp-syn) != 0'

But I am getting the error:
Code:
tcpdump: no suitable device found

Is there an alternate command to achieve this?

Last edited by Don Cragun; 05-11-2015 at 05:01 PM.. Reason: Add missing CODE tags.
# 2  
Are you root?
# 3  
Yes I am root.
# 4  
Traditionally, you must specify a device. Therefore

Code:
tcpdump -i eth0 -w /tmp/syn.pcap 'tcp[tcpflags] & (tcp-syn) != 0'

But that assumes you want it from eth0. Maybe you want it from wlan0. But maybe your system currently has no interfaces that are up. That would explain why you're not seeing any tcp packets and are resorting to tcpdump in the first place.

Also, the output will be to that file so you won't know it's working right away. Try it without -w... until you get some output.
# 5  
tcpdump: BIOCVERSION: Invalid argument is the output I get

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