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I'm running gkrellm which shows that some process on my Debian Linux system is writing approx 500KB/s to eth0. I'd like to find out which process it is. I know a little bit about netstat, but it shows a gazillion open TCP connections and I can't seem to make it produce any information about traffic.

Does anybody know how I can get a list of processes that are actually using the eth0 interface so that I can track down the offender?

FOLLOWUP: The Debian Linux distribution contains a nethogs package which solves this problem definitively. Related tools that are not quite on the mark include iftop, netstat, and lsof.

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up vote 11 down vote accepted

I prefer nethogs. It's a small ncurses-based console program that displays per-process network traffic status in a convenient way.

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netstat -ptu will give you the owning process ids (along with standard netstat info) for all tcp and udp conections. (Normal users will not be able to id all processes.)

If something is sending out a fair amount of constant traffic you should see it on Recv-Q or Send-Q columns 2 and 3 respectively.

sudo watch -n .1 'netstat -tup | grep -E "^[t,u]cp[6]{0,1}" | sort -nr -k2'

sudo watch -n .1 'netstat -tup | grep -E "^[t,u]cp[6]{0,1}" | sort -nr -k3'

If you suspect that that process is being triggered by another process ps axf.

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(Not that the -u flag in necessary if you know that you are looking for TCP connections.) – andol Sep 29 '11 at 6:24

A more manual operation if you are looking for just a process sending/receiving data would be to run the lsof command. This will list all open files for each process which will include network connections as they are file descriptors to the o.s.

Not sure if this is what you are looking for.

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Install iftop (simple text-based) or ntop (graphical).

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iftop only display bandwidth usage on an interface. – quanta Sep 29 '11 at 2:41
It shows much more than that. By default, it breaks it down by host. – David Schwartz Sep 29 '11 at 2:42
Can it list all processes that are using an interface? If so, could you please show us the command and options? – quanta Sep 29 '11 at 2:48
Not directly. But once you find the host, you can find the process, for example with netstat -pn. – David Schwartz Sep 29 '11 at 2:49

Use tcpdump to sniff some packets on this interface:

# tcpdump -vv -s0 -i eth0 -c 100 -w /tmp/eth0.pcap

Copy to client and open with Wireshark to see what happens.

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Not the easiest way to get simple stats but anything even slightly more complicated and wireshark will shine! – Silverfire Oct 19 '11 at 5:57

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