And the Time Is …

Charly's Column – ntpviz

Article from Issue 228/2019

The Network Time Protocol allows admins to keep time on their computers. Due to the way the system works, this timekeeping is only moderately successful. Charly uses the ntpviz statistics tool to visualize time fluctuation.

I recently browsed the NTPsec repository [1], a heavily reworked fork of the well-known Network Time Protocol daemon, ntpd. The newcomer is looking to ditch legacy ballast and finally provide protection against Man-in-the-Middle attacks. NTPsec is not the topic today, but I would like to talk about a small tool that I found while browsing: ntpviz. Among other things, the program visualizes the extent to which the time queried by the NTP server deviates from the local time (offset) and how strongly it fluctuates (jitter).

To get started, I cloned the Github repository and started the installation:

cd /usr/local
git clone --depth 1
cd ntpsec
./waf configure --refclock=all && ./waf build && ./waf install

Then I created the directory where the statistics data will be stored:

mkdir /var/log/ntpstats

What's missing is /etc/ntp.conf from Listing 1. Now I can start the NTP daemon. With the parameter -N it runs with increased priority – this improves the accuracy:

ntpd -c /etc/ntp.conf -N

Listing 1



Now, I have a day off – after all, ntpd has to collect enough statistics. Typing

ntpviz @day/optionfile

was supposed to start the visualization, but it blew up in my face the first time I tried it. It turns out that Gnuplot has to be installed – a fact that slipped by me when checking the dependencies. After installing Gnuplot everything runs like clockwork: The www/day subdirectory contains an HTML file with various graphs (Figure 1).

Figure 1: Jitter statistics of four NTP servers queried over a period of 12 hours.

The Author

Charly Kühnast manages Unix systems in the data center in the Lower Rhine region of Germany. His responsibilities include ensuring the security and availability of firewalls and the DMZ.

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