netsniff-ng is a free Linux networking toolkit, a Swiss army knife for your daily Linux network plumbing if you will. Its gain of performance is reached by zero-copy mechanisms, so that on packet reception and transmission the kernel does not need to copy packets from kernel space to user space and vice versa.


Security Onion uses netsniff-ng to collect full packet capture in the form of pcap files.


netsniff-ng writes full packet capture in the form of pcap files to:
  • HOSTNAME is your actual hostname
  • INTERFACE is your actual sniffing interface
  • YYYY-MM-DD is the year, month, and date the pcap was recorded


Besides accessing the pcaps in the directory shown above, you can also pivot to full packet capture from Sguil and CapMe.


Check the netsniff-ng.log file in /var/log/nsm/HOSTNAME-INTERFACE/netsniff-ng.log (where HOSTNAME is your actual hostname and INTERFACE is your actual sniffing interface).


If sostat report packet loss in netsniff-ng, you may want to consider one or more of the following options in /etc/nsm/HOSTNAME-INTERFACE/sensor.conf:

  • increase PCAP_RING_SIZE
  • set PCAP_OPTIONS to --mmap to enable memory-mapped IO


Both of these options will cause netsniff-ng to consume more RAM.

Reducing Storage

Full packet capture obviously requires lots of disk space. Trimming your pcaps can allow you to store pcap for longer periods of time. For more information, please see the Trimming PCAPs section.

More Information

For more information about netsniff-ng, please see