tcpdump inside a shell script captures nothing
linux, tcpdump
Solution
Don't use `kill -9`. Not only is it almost always the wrong thing to do, it might be causing the problem here, by having buffered data be discarded rather than written to disk. Use plain old kill, or `kill -2`.
Another option is to add in the `-U` option to flush the output buffer after every packet.
Problem
I want to start a TCP program and capture the related packets, my shell script `cap.sh` is as below: ``` sudo tcpdump -i eth0 -w mypcap & sleep 3 ./tcp_receiver sleep 2 x=`ps -ef|grep "tcpdump"|grep -v "grep"|awk '{print $2}'` sudo kill -9 $x ``` I run `cap.sh` ``` sudo ./cap.sh ``` so actually in this shell, I can run `sudo` without password and the host just a virtual slice on a remote machine (PLanetlab node) although I can see the process `tcpdump` from `ps -ef` it captures nothing I see the `mypcap` file is 0 bytes after the `cap.sh` finishes what are potential reasons? and how to make the tcpdump in a shell script capture the packets? thanks!