Highly accurate system time
On Time for All Time
After the idea of procuring an atomic clock failed to thrill the other members of Charly's household, our intrepid columnist simply decided to tap into the timekeeping of a GPS satellite. In doing so, he ensured the kind of punctuality at home that only large data centers actually need. Precisely.
The network time protocol (NTP) is one of the easiest server-based services to configure. The ntp.conf
file requires minimal configuration; just one line with a source from which to tell the time.
pool de.pool.ntp.org iburst
You usually specify more than one source. The NTP daemon (ntpd) queries it cyclically and tries to compute running time differences caused by network latency. My local NTP service runs on a Raspberry Pi (Rasp Pi), otherwise employed full-time in driving the garden irrigation system, and has a time imprecision of 30 to 40msec.
This may be almost indecently accurate for my always slightly chaotic household, but logging with millisecond accuracy is a genuine requirement for data centers. How far can I take this newly inspired punctuality madness?
First of all, I need to reduce the stratum. A highly accurate time source that makes its time signal available to the public is a stratum-0 device. A server that requests the time from it, and distributes the results, is a stratum-1 server, and so on.
The obvious idea of buying an atomic clock strangely failed to meet approval in our family council. This prompted me to provide my Rasp Pi with a GPS receiver – any GPS satellite is a stratum-0 time source. The GPS daemon, included in the scope of most distributions, provides the time signal to the NTP server via a virtual interface. I then added two lines to the ntp.conf
file to introduce the NTP daemon to the address:
server 127.127.28.0 minpoll4 noselect fudge 127.127.28.0 time1 0.0 refid GPS
That's better; however, you can achieve even more precision, because transporting the data through the serial interface can still produce slight variations. You can compute these yourself: GPS satellites do not just transmit the time, but also a pulse per second (PPS) signal. These are short, high-precision pulses output every second.
A small tool named rpi_gpio_ntp
[1] by programmer Folkert van Heusden makes the PPS signal accessible to the time server. Again, a virtual IP is used for this, which I entered in my ntp.conf
:
server 127.127.28.1 minpoll 4 prefer fudge 127.127.28.1 refid UPPS
This was amazingly successful. My Munin graph in Figure 1, which shows the fluctuations of the time signal, flattens out to a smooth line after firing up the GPS-PPS combination – not bad for a stratum-1 time server.
Time To Go Time
Ntpd is currently dying out on clients in the wake of systemd, replace by timesyncd. Although timesyncd is leaner, it does not propagate to the clients. I configured it in my /etc/systemd/timesyncd.conf
file so that it primarily uses my irrigation Rasp Pi and only turns into Internet time servers in an emergency:
NTP=gpspi FallBackNTP=de.pool.ntp.org 0.pool.ntp.org 1.pool.ntp.org
If the day ever comes when I have accumulated enough hardware to require high-precision logging, now I'm prepared.
Infos
- rpi_gpio_ntp: https://vanheusden.com/time/rpi_gpio_ntp/
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Direct Download
Read full article as PDF:
Price $2.95
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Find SysAdmin Jobs
News
-
The Next Major Release of Elementary OS Has Arrived
It's been over a year since the developers of elementary OS released version 6.1 (Jólnir) but they've finally made their latest release (Horus) available with a renewed focus on the user.
-
KDE Plasma 5.27 Beta Is Ready for Testing
The latest beta iteration of the KDE Plasma desktop is now available and includes some important additions and fixes.
-
Netrunner OS 23 Is Now Available
The latest version of this Linux distribution is now based on Debian Bullseye and is ready for installation and finally hits the KDE 5.20 branch of the desktop.
-
New Linux Distribution Built for Gamers
With a Gnome desktop that offers different layouts and a custom kernel, PikaOS is a great option for gamers of all types.
-
System76 Beefs Up Popular Pangolin Laptop
The darling of open-source-powered laptops and desktops will soon drop a new AMD Ryzen 7-powered version of their popular Pangolin laptop.
-
Nobara Project Is a Modified Version of Fedora with User-Friendly Fixes
If you're looking for a version of Fedora that includes third-party and proprietary packages, look no further than the Nobara Project.
-
Gnome 44 Now Has a Release Date
Gnome 44 will be officially released on March 22, 2023.
-
Nitrux 2.6 Available with Kernel 6.1 and a Major Change
The developers of Nitrux have officially released version 2.6 of their Linux distribution with plenty of new features to excite users.
-
Vanilla OS Initial Release Is Now Available
A stock GNOME experience with on-demand immutability finally sees its first production release.
-
Critical Linux Vulnerability Found to Impact SMB Servers
A Linux vulnerability with a CVSS score of 10 has been found to affect SMB servers and can lead to remote code execution.