Synchronization

Introduction

Accurate timekeeping is integral to modern software deployments. Without it, you may encounter data corruption, errors, and other issues that are difficult to debug. Time synchronization can help ensure your logs are being recorded in the correct order, and that database updates are appropriately applied.

Fortunately, Ubuntu 20.04 has time synchronization built-in and activated by default using systemd’s timesyncd service. In this article, you will practice some general time-related commands, verify that timesyncd is active, and install an alternate network time service.

Prerequisites

Before starting this tutorial, you will need an Ubuntu 20.04 server with a non-root, sudo-enabled user and a firewall, as described in this Ubuntu 20.04 server setup tutorial.

Navigating Basic Time Commands

To view the time on your server, you will use the command date. Any user can run this command to print out the date and time:

Typically, your server will generate an output with the default UTC time zone.

Output
Thu Aug 5 15:55:20 UTC 2021

UTC is Coordinated Universal Time, the time at zero degrees longitude. While this may not reflect your current time zone, using Universal Time prevents confusion when your infrastructure spans multiple time zones.

If you want to change your time zone, however, you can use the timedatectl command.

First, run this command to generate a list of 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.

Next, you can set the time zone with timedatectl set-timezone by replacing the highlighted portion 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:

Output
Thu Aug 5 11:56:01 EDT 2021

The time zone abbreviation will reflect the newly chosen value.

Now that you’ve practiced checking the clock and setting time zones, you can confirm that your time is being synchronized properly in the next section.

Controlling timesyncd with timedatectl

Previously, 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.

But now with Ubuntu’s default install, you can use timesyncd instead of ntpd. timesyncd works similarly by connecting to the same time servers, but is llightweight and more closely integrated with systemd on Ubuntu.

You can query the status of timesyncd by running timedatectl with no arguments. You don’t need to use sudo in this case:

Output
                     Local time: Thu 2021-08-05 11:56:40 EDT
           Universal time: Thu 2021-08-05 15:56:40 UTC
                 RTC time: Thu 2021-08-05 15:56:41
                Time zone: America/New_York (EDT, -0400)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

This command 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 reflects that the time is successfully synced, and NTP service: active means that timesyncd is up and running.

If your output shows that NTP service isn’t active, turn it on with timedatectl:

sudo timedatectl set-ntp on

After this, run timedatectl again to confirm the network time status. It may take a minute for the sync to happen, but eventually System clock synchronized: will read yes and NTP service: will show as active.

Switching to ntpd

timesyncd will work in most circumstances. There are instances, however, when an application may be sensitive to any disturbance with time. In this case, ntpd is an alternative network time service you can use. ntpd uses sophisticated techniques to constantly and gradually keep the system time on track.

Before installing ntpd, you need to turn off timesyncd in order to prevent the two services from conflicting with one another. You can do this by disabling network time synchronization with the following command:

sudo timedatectl set-ntp no

Verify that time synchronization is disabled:

Check that your output reads NTP service: inactive. This means timesyncd has stopped. Now you’re ready to install the ntp package with apt.

First, run apt update to refresh your local package index:

Then, run apt install ntp to install this package:

ntpd will begin automatically after your installation completes. You can verify that everything is working correctly by querying ntpd for status information:

Output
           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
+t1.time.bf1.yah 129.6.15.28      2 u   16   64    1   61.766  -20.068   1.964
+puppet.kenyonra 80.72.67.48      3 u   16   64    1    2.622  -18.407   2.407
*ntp3.your.org   .GPS.            1 u   15   64    1   50.303  -17.499   2.708
+time.cloudflare 10.4.1.175       3 u   15   64    1    1.488  -18.295   2.670
+mis.wci.com     216.218.254.202  2 u   15   64    1   21.527  -18.377   2.414
+ipv4.ntp1.rbaum 69.89.207.99     2 u   12   64    1   49.741  -17.897   3.417
+time.cloudflare 10.4.1.175       3 u   15   64    1    1.039  -16.692   3.378
+108.61.73.243   129.6.15.29      2 u   14   64    1   70.060  -16.993   3.363
+ny-time.gofile. 129.6.15.28      2 u   21   64    1   75.349  -18.333   2.763
 golem.canonical 17.253.34.123    2 u   28   64    1  134.482  -21.655   0.000
 ntp3.junkemailf 216.218.254.202  2 u   19   64    1    2.632  -16.330   4.387
 clock.xmission. .XMIS.           1 u   18   64    1   24.927  -16.712   3.415
 alphyn.canonica 142.3.100.2      2 u   26   64    1   73.612  -19.371   0.000
 strongbad.voice 192.5.41.209     2 u   17   64    1   70.766  -18.159   3.481
 chilipepper.can 17.253.34.123    2 u   25   64    1  134.982  -19.848   0.000
 pugot.canonical 145.238.203.14   2 u   28   64    1  135.694  -21.075   0.000

ntpq is a query tool for ntpd. The -p flag requests information about the NTP servers (or peers) ntpd is connected to. Your output will be slightly different but will list the default Ubuntu pool servers plus a few others. Remember, it can take a few minutes for ntpd to establish connections.

Conclusion

In this article, you’ve successfully viewed the system time, changed time zones, worked with Ubuntu’s default timesyncd service, and installed ntpd. If you have advanced timekeeping needs, you can reference the official 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.