pfSense ntopng export flows to ELK stack for monitoring

A more detailed step by step tutorial might follow on how to setup ELK stack etc…

For now, I am going to assume you have ntopng installed on a pfSense and already have an ELK stack running and ready to collect data

pfSense & ntopng woes

The experience of running ntopng in pfSense is a neverending problem. Some have no problems, while most just can’t get it to “stay” running properly. Personally, I had 3 different pfSense boxes for testing before deployment, and sometimes they work, sometimes they don’t

kernel pid 00000 (ntopng), uid 0: exited on signal 11 (core dumped)



If you are looking at the Lua.cpp error, stop there. It won’t help, because sometimes this won’t come out at all and ntopng just stops running with a “signal 11”

The quick layman fix/workaround

I am not proficient enough to debug or help solve these ntopng FreeBSD ports, and don’t really want to start now. For a start, let’s have ntopng restart whenever it stops running

The end goal is to have ELK collect flows/data from ntopng. In summary, ntopng can restart multiple times for all I care

What you get from this fix/workaround method:

  • You can still monitor real-time (almost) bandwidth using ntopng, with that usual page not loading (as it has stopped and will be restarted by Service Watchdog). Host duration will be reset as ntopng itself restarts
  • Via ELK, you can graph, filter out specific devices/IPs and its historical data/flows

Service Watchdog

Make use of pfSense’s Services >> Service Watchdog to restart the ntopng service whenever it stops.

This should be pretty forward, just add the ntopng service into the Watchdog. Disable notifications if you know ntopng is going to keep restarting every 15~30mins

Add ntopng export flows option

Right, you will need to add ‘ -F ‘ option to your ntopng service

Example option to ELK stack hosted in device would be:

-F 'es;ntopng;ntopng-%Y.%m.%d;;' -D all

“-D all” is optional. This tells ntopng to dump all hostnames, which will populate SSL and HTTP hostnames in Kibana later

To edit ntopng run options, go to Diagnostics >> Edit File

under “Path to file to be edited”, enter


Click “Load” and you will see the ntopng run options

Proceed to edit the following line:

	/usr/local/bin/ntopng -d /var/db/ntopng -G /var/run/ -s -e -w 0 -W 3000    -i 'xn2' -i 'xn0' --dns-mode '1'  --local-networks ',,' &

Append your ” – F ” config into that line above, it can be anywhere after /usr/local/bin/ntopng , I usually paste the command somewhere in between -W and -i

Once you have done that, your new ntopng command will be the following:

	/usr/local/bin/ntopng -d /var/db/ntopng -G /var/run/ -s -e -w 0 -W 3000 -F 'es;ntopng;ntopng-%Y.%m.%d;;' -D all  -i 'xn2' -i 'xn0' --dns-mode '1'  --local-networks ',,' &

Ensure you are using

' '

to surround the command. Previously I had this command listed in my Evernote which autocorrected it to ” ” or ` `, breaking ntopng. Even WordPress converts it to ‘ ‘, which is also different

Proceed to click on “Save” where you first clicked on the “Load” button

Making it stick

Since ntopng will be restarting most of the time, you will need to ensure that your ntopng will always run with the new ” -F ” option above, and also survive a reboot of pfSense

After adding the new ” -F ” command as above, go to Diagnostics >> Command Prompt

Run the following command under “Execute Shell Command” field

chflags schg /usr/local/etc/rc.d/

and click on “Execute”, you will not see any result.

This command locks the file. It will survive reboots and also enabling/disabling via Diagnostics >> ntopng Settings GUI

To unlock the file

chflags noschg /usr/local/etc/rc.d/

Do remember to unlock the file if you want to uninstall, reinstall, make changes to ntopng

Login to ntopng and check that it has the new options loaded by going to Home Icon >> Runtime Status, you should see the change and flow in Startup Line and Log Trace

Voila, ntopng is successfully sending flows to your ELK stack

Kibana Dashboard & ELK tips, hints & note

Now you have the ability to search, filter out, create custom graphs on historical data. Assuming you have already successfully collected the ntopng flows and enjoying the regret of spending even more time on making visualizations and dashboards.


Note if you are monitoring your local LAN network:

IN_BYTES = Upload

OUT_BYTES = Download

Under Kibana Index fields format, you can change IN_BYTES, OUT_BYTES, to “Bytes” to tell Kibana to show them in Bytes format


Take great care of your hard disk space, as MySQL or ELK indices can be really large if you have large flows.

A 20Mbps/20Mbps Download Upload WAN, 8am – 10pm, with after hours having the least flows

will produce daily indices of sizes around 1~1.5GB. Your indices size will vary accordingly to the usage of your network

Check out ELK’s documentation  on how to delete indices

Minor problems not related to pfSense

ntopng’s elasticsearch flow template (multiple index mapping types) is not supported in the latest ELKv6 stack. The most obvious one would be geographical and IP addresses data not being mapped properly. You can read more about this from ntopng’s blog

ntopng goes Elastic: Introducing ElasticSearch 6 Support

Fix? Run a separate machine/VM, bridge your interfaces, run ntopng 3.5 nightly build and send the new flows to ELK v6

Or you can use ELK v5 which supports multiple index mapping types

Note: I have not tried any of the above

Exporting ntopng Flows to MySQL

The command will be as follows (choose only one, ElasticSearch or MySQL, not both)

-F 'mysql;;ntopng;flows;mysql_username;mysql_db_password'

Other weird notes

After experimenting with exporting flows to MySQL or ELK, it seems that if you were to dump the flows elsewhere, ntopng stops restarting in pfSense. It definitely worked for me, only time will tell. Would appreciate it if anyone care to comment if this method works for them?