Recently we needed to process the results of a
tcpdump command using the GUI version of
WireShark on machine that did not have a window manager installed. That device was an embedded device, for which it did not make sense to even consider installing a window manager on it. So, in order to process the results of the
tcpdump command we decided to use another machine that had a full working window manager installed and was able to operate the GUI version of
For our solution to work some requirements were expected to be met by the embedded device (a.k.a. remote machine).
tcpdumpwas installed on the remote machine
ssh serverwas installed on the remote machine and allowed us to connect to it remotely
- there was a user that had remote ssh rights on the remote machine that also had the rights to execute
tcpdumpon the needed interfaces
Synopsis of our solution:
Just execute the following on the machine with the GUI (a.k.a. local machine)
mkfifo /tmp/board; wireshark -k -i /tmp/board & ssh [email protected] "tcpdump -s 0 -U -n -w - -i lo not port 22" > /tmp/board;
Explanation of our solution:
Following are the steps that we performed on the local machine to
pipe the results of
tcpdump on the remote machine on the
wireshark on the local machine.
- First we created a
named pipeas follows:
You can name your
pipeanyway you like and place it in any folder you wish. We used
pipeis a temporary construct that we do not care to preserve across time/restarts.
- Then we started
wiresharkfrom a terminal so that we could pass as capture interface the
named pipewe just created using the
-i /tmp/boardparameter. The
wiresharkto start the capture session immediately.
wireshark -k -i /tmp/board &
Since this operation was going to execute for a long time, we sent it to the background to release the terminal for further use by placing the
&symbol at the end of the command.
- Finally, we started
sshon a board and redirected its output to our
ssh [email protected] "tcpdump -s 0 -U -n -w - -i lo not port 22" > /tmp/board;
The parameters we used on
tcpdumphave the following effects:
tcpdumpto set the snapshot length of data from each packet to the default value of
-woption is not specified, make the printed packet output
packet-buffered. Which means that it will print the description of the contents of each packet without waiting for the output buffer to get full.
-nDoes not convert host addresses to names. This can be used to avoid DNS lookups.
-w -Write the raw packets to
Standard Outputrather than parsing them.
-i loDefines which interface to listen on. We wanted the loopback interface to listen to everything.
not port 22Since we used
sshto start this command, we do not want to listen to the data that we produce as well and flood the inputs.