Introduction
Accurate timekeeping has become a critical component of modern software deployments. Whether it’s making sure logs are recorded in the right order or database updates are applied correctly, out-of-sync time can cause errors, data corruption, and other hard to debug issues.
Ubuntu 18.04 has time synchronization built in and activated by default using systemd’s timesyncd service. In this article we will look at some basic time-related commands, verify that timesyncd is active, and learn how to install an alternate network time service.
Prerequisites
Before starting this tutorial, you will need an Ubuntu 18.04 server with a non-root, sudo-enabled user, as described in this Ubuntu 18.04 server setup tutorial.
Navigating Basic Time Commands
The most basic command for finding out the time on your server is date. Any user can type this command to print out the date and time:
date
Tue Jul 10 14:48:52 UTC 2018
Most often your server will default to the UTC time zone, as highlighted in the above output. UTC is Coordinated Universal Time, the time at zero degrees longitude. Consistently using Universal Time reduces confusion when your infrastructure spans multiple time zones.
If you have different requirements and need to change the time zone, you can use the timedatectl command to do so.
First, list the available time zones:
timedatectl list-timezones
A list of time zones will print to your screen. You can press SPACE to page down, and b to page up. Once you find the correct time zone, make note of it then type q to exit the list.
Now set the time zone with timedatectl set-timezone, making sure to replace the highlighted portion below with the time zone you found in the list. You’ll need to use sudo with timedatectl to make this change:
sudo timedatectl set-timezone America/New_York
You can verify your changes by running date again:
date
Tue Jul 10 10:50:53 EDT 2018
The time zone abbreviation should reflect the newly chosen value.
Now that we know how to check the clock and set time zones, let’s make sure our time is being synchronized properly.
Controlling timesyncd with timedatectl
Until recently, most network time synchronization was handled by the Network Time Protocol daemon or ntpd. This service connects to a pool of other NTP servers that provide it with constant and accurate time updates.
Ubuntu’s default install now uses timesyncd instead of ntpd. timesyncd connects to the same time servers and works in roughly the same way, but is more lightweight and more integrated with systemd and the low level workings of Ubuntu.
We can query the status of timesyncd by running timedatectl with no arguments. You don’t need to use sudo in this case:
timedatectl
Local time: Tue 2018-07-10 10:54:12 EDT
Universal time: Tue 2018-07-10 14:54:12 UTC
RTC time: Tue 2018-07-10 14:54:12
Time zone: America/New_York (EDT, -0400)
System clock synchronized: yes
systemd-timesyncd.service active: yes
RTC in local TZ: no
This prints out the local time, universal time (which may be the same as local time, if you didn’t switch from the UTC time zone), and some network time status information. System clock synchronized: yes indicates that the time has been successfully synced, and systemd-timesyncd.service active: yes means that timesyncd is enabled and running.
If timesyncd isn’t active, turn it on with timedatectl:
sudo timedatectl set-ntp on
Run timedatectl again to confirm the network time status. It may take a minute for the actual sync to happen, but eventually both Network time on: and NTP synchronized: should read yes.
Switching to ntpd
Though timesyncd is fine for most purposes, some applications that are very sensitive to even the slightest perturbations in time may be better served by ntpd, as it uses more sophisticated techniques to constantly and gradually keep the system time on track.
Before installing ntpd, we should turn off timesyncd:
sudo timedatectl set-ntp no
Verify that timesyncd is off:
timedatectl
Look for systemd-timesyncd.service active: no in the output. This means timesyncd has been stopped. We can now install the ntp package with apt:
sudo apt update
sudo apt install ntp
ntpd will be started automatically after install. You can query ntpd for status information to verify that everything is working:
ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
0.ubuntu.pool.n .POOL. 16 p - 64 0 0.000 0.000 0.000
1.ubuntu.pool.n .POOL. 16 p - 64 0 0.000 0.000 0.000
2.ubuntu.pool.n .POOL. 16 p - 64 0 0.000 0.000 0.000
3.ubuntu.pool.n .POOL. 16 p - 64 0 0.000 0.000 0.000
ntp.ubuntu.com .POOL. 16 p - 64 0 0.000 0.000 0.000
+ec2-52-0-56-137 216.239.35.0 2 u 16 64 1 7.872 -2.137 1.485
+66.220.10.2 129.6.15.30 2 u 12 64 1 65.204 3.740 2.686
+block.steinhoff 209.51.161.238 2 u 11 64 1 33.364 1.710 3.586
+eterna.binary.n 216.229.0.50 3 u 11 64 1 35.330 2.821 2.839
+2604:a880:800:1 209.51.161.238 2 u 14 64 1 0.394 0.386 2.462
+ec2-52-6-160-3. 130.207.244.240 2 u 11 64 1 8.150 2.050 3.053
+mx.danb.email 127.67.113.92 2 u 13 64 1 63.868 1.539 2.240
*hydrogen.consta 129.6.15.28 2 u 12 64 1 2.989 1.755 2.563
+ntp-3.jonlight. 127.67.113.92 2 u 10 64 1 64.561 2.122 3.593
+undef.us 45.33.84.208 3 u 12 64 1 33.508 1.631 3.647
+ntp-3.jonlight. 127.67.113.92 2 u 8 64 1 64.253 2.645 3.174
2001:67c:1560:8 145.238.203.14 2 u 22 64 1 71.155 -1.059 0.000
+test.diarizer.c 216.239.35.4 2 u 11 64 1 64.378 4.648 3.244
2001:67c:1560:8 145.238.203.14 2 u 18 64 1 70.744 -0.964 0.000
alphyn.canonica 132.246.11.231 2 u 17 64 1 7.973 -0.170 0.000
+vps5.ctyme.com 216.218.254.202 2 u 10 64 1 65.874 1.902 2.608
ntpq is a query tool for ntpd. The -p flag asks for information about the NTP servers (or peers) ntpd has connected to. Your output will be slightly different, but should list the default Ubuntu pool servers plus a few others. Bear in mind that it can take a few minutes for ntpd to establish connections.
Conclusion
In this article we’ve shown how to view the system time, change time zones, work with Ubuntu’s default timesyncd, and install ntpd. If you have more sophisticated timekeeping needs than what we’ve covered here, you might reference the offical NTP documentation, and also take a look at the NTP Pool Project, a global group of volunteers providing much of the world’s NTP infrastructure.
