I'm using tcpdump for a rotating network traffic capture, and Moloch as a nice viewer for the data. The problem is that tcpdump appends a number to the end of the filename, while Moloch only uses files that end in .pcap.

Is there a way to set up tcpdump to create filenames ending in .pcap?

Using a date format string doesn't work because I need the filenames to repeat (after every 20 files or so).

sudo tcpdump -i eth0 -s 0 -W 4 -G 15 -C 1 -w ./dump.pcap

  • 1
    Seems like it would be super easy to modify tcpdump to put the number before the .pcap. Maybe even offer it as a pull request to the core maintainers. @guyharris
    – Spiff
    Jul 4, 2018 at 21:07

1 Answer 1


I figure tcpdumps "postrotate-command" can be used for this. tcpdump [...] -z <command> will call the command after each capture with the current filename, hence I presume you should be able to rename files with it, if you do the renaming in a small shell script:

-z postrotate-command Used in conjunction with the -C or -G options, this will make tcpdump run " postrotate-command file " where file is the save- file being closed after each rotation. For example, specifying -z gzip or -z bzip2 will compress each savefile using gzip or bzip2.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.