The sys admin's daily grind: Ntpd
Borrowed Time
The Network Time Protocol keeps Charly up to date at all times. To put all of this punctuality in the service of the common good, he even exports the time signal.
If the clock on my personal laptop is a few seconds fast or slow, this is not dramatic. On a server, however, it's different. Logfiles should – at least – be synchronized to the exact second; otherwise, troubleshooting becomes a pain. The software that handles this synchronization is, of course, the NTP daemon (ntpd
) [1]. As a special hardware time source, you could use a suitable DCF 77 or GPS receiver, for example. If you don't have one of those, you could ask some other time servers – you need to poll several to compute the time from the running time differences of the UDP packets on the network.
The NTP configuration in the /etc/ntp.conf
file on my Ubuntu lab machine lists five time servers:
server ntps1-0.cs.tu-berlin.de iburst server ptbtime1.ptb.de iburst server ntp1.fau.de iburst server ntp.probe-networks.de iburst # Use Ubuntu's ntp server as a fallback. server ntp.ubuntu.com
The iburst
("initial burst") keyword speeds up synchronization on the first connection. A list of public time servers is available online [2].
Borrowed Time
Just to check, I entered ntpq-p
at the command line; this returned a list of all the time servers that my daemon contacted (Figure 1). The first column shows how reliable the time sources are: An asterisk (*
) denotes the current reference server. A plus sign means that the time from this server is used to compute the mean value. Servers with a minus sign have recently supplied times with too large of a deviation – if this problem were to exist permanently, I would need to delete them from the configuration.
Sharing Free Time
Furthermore, nothing prevents me from providing my time server to others. The expected traffic is minimal, and the safety risks are also minimal if this setup is configured correctly. Specifically, in /etc/ntp.conf
, I need to stipulate that external NTP clients can retrieve time information but not configure anything. The following lines do the trick:
restrict -4 default kod notrap nomodifynopeer noquery restrict -6 default kod notrap nomodifynopeer noquery
If you do not use IPv6, you can leave out the second line, of course.
How do other users learn about my time server? The best way is to add it to a popular time network like pool.ntp.org [3]. A working ntpd is the only prerequisite for time servers; you can complete a web form for the actual entries. The more people to join, the less the load per server, and most importantly: We all have more free time (Figure 2).
Infos
- NTP daemon: http://www.eecis.udel.edu/~mills/ntp/html/ntpd.html
- List of public time servers: http://support.ntp.org/bin/view/Servers/WebHome#Browsing_the_Lists
- Time server network ntp.org: http://www.pool.ntp.org/en/join.html
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
Red Hat Adds New Deployment Option for Enterprise Linux Platforms
Red Hat has re-imagined enterprise Linux for an AI future with Image Mode.
-
OSJH and LPI Release 2024 Open Source Pros Job Survey Results
See what open source professionals look for in a new role.
-
Proton 9.0-1 Released to Improve Gaming with Steam
The latest release of Proton 9 adds several improvements and fixes an issue that has been problematic for Linux users.
-
So Long Neofetch and Thanks for the Info
Today is a day that every Linux user who enjoys bragging about their system(s) will mourn, as Neofetch has come to an end.
-
Ubuntu 24.04 Comes with a “Flaw"
If you're thinking you might want to upgrade from your current Ubuntu release to the latest, there's something you might want to consider before doing so.
-
Canonical Releases Ubuntu 24.04
After a brief pause because of the XZ vulnerability, Ubuntu 24.04 is now available for install.
-
Linux Servers Targeted by Akira Ransomware
A group of bad actors who have already extorted $42 million have their sights set on the Linux platform.
-
TUXEDO Computers Unveils Linux Laptop Featuring AMD Ryzen CPU
This latest release is the first laptop to include the new CPU from Ryzen and Linux preinstalled.
-
XZ Gets the All-Clear
The back door xz vulnerability has been officially reverted for Fedora 40 and versions 38 and 39 were never affected.
-
Canonical Collaborates with Qualcomm on New Venture
This new joint effort is geared toward bringing Ubuntu and Ubuntu Core to Qualcomm-powered devices.