Port flow capture

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# 1  
Old 05-11-2015
Port flow capture

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

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

Is there an alternate command to achieve this?

Last edited by Don Cragun; 05-11-2015 at 04:01 PM.. Reason: Add missing CODE tags.
# 4  
Old 05-11-2015
Traditionally, you must specify a device. Therefore

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.
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