How To Set Up Time Synchronization on Debian 10

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 difficult issues to debug.

Debian 10 has time synchronization built in and activated by default using the standard ntpd time server, provided by the ntp package. In this article we will look at some basic time-related commands, verify that ntpd is active and connected to peers, and learn how to activate the alternate systemd-timesyncd network time service.

Prerequisites

Before starting this tutorial, you will need a Debian 10 server with a non-root, sudo-enabled user, as described in this Debian 10 server setup tutorial.

Step 1 — 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

Output
Wed 31 Jul 2019 06:03:19 PM UTC

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

Output
Wed 31 Jul 2019 02:08:43 PM EDT

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.

Step 2 — Checking the Status of ntpd

By default, Debian 10 runs the standard ntpd server to keep your system time synchronized with a pool of external time servers. We can check that it’s running with the systemctl command:

sudo systemctl status ntp

Output
● ntp.service - Network Time Service
   Loaded: loaded (/lib/systemd/system/ntp.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2019-07-31 13:57:08 EDT; 17min ago
     Docs: man:ntpd(8)
 Main PID: 429 (ntpd)
    Tasks: 2 (limit: 1168)
   Memory: 2.1M
   CGroup: /system.slice/ntp.service
           └─429 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -u 106:112
. . .

The active (running) status indicates that ntpd started up properly. To get more information about the status of ntpd we can use the ntpq command:

ntpq -p

Output
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 0.debian.pool.n .POOL.          16 p    -   64    0    0.000    0.000   0.000
 1.debian.pool.n .POOL.          16 p    -   64    0    0.000    0.000   0.000
 2.debian.pool.n .POOL.          16 p    -   64    0    0.000    0.000   0.000
 3.debian.pool.n .POOL.          16 p    -   64    0    0.000    0.000   0.000
+208.67.72.50    152.2.133.55     2 u   12   64  377   39.381    1.696   0.674
+198.46.223.227  204.9.54.119     2 u    6   64  377   22.671    3.536   1.818
-zinc.frizzen.ne 108.61.56.35     3 u   43   64  377   12.012    1.268   2.553
-pyramid.latt.ne 204.123.2.72     2 u   11   64  377   69.922    2.858   0.604
+nu.binary.net   128.252.19.1     2 u   10   64  377   35.362    3.148   0.587
#107.155.79.108  129.7.1.66       2 u   65   64  377   42.380    1.638   1.014
+t1.time.bf1.yah 98.139.133.62    2 u    6   64  377   11.233    3.305   1.118
*sombrero.spider 129.6.15.30      2 u   47   64  377    1.304    2.941   0.889
+hydrogen.consta 209.51.161.238   2 u   45   64  377    1.830    2.280   1.026
-4.53.160.75     142.66.101.13    2 u   42   64  377   29.077    2.997   0.789
#horp-bsd01.horp 146.186.222.14   2 u   39   64  377   16.165    4.189   0.717
-ntpool1.603.new 204.9.54.119     2 u   46   64  377   27.914    3.717   0.939

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

Step 3 — Switching to systemd-timesyncd

It is possible to use systemd’s built-in timesyncd component to replace ntpd. timesyncd is a lighter-weight alternative to ntpd that is more integrated with systemd. Note, however, that it doesn’t support running as a time server, and it is slightly less sophisticated in the techniques it uses to keep your system time in sync. If you are running complex real-time distributed systems, you may want to stick with ntpd.

To use timesyncd, we must first uninstall ntpd:

sudo apt purge ntp

Then, start up the timesyncd service:

sudo systemctl start systemd-timesyncd

Finally, check the status of the service to make sure it’s running:

sudo systemctl status systemd-timesyncd

Output
● systemd-timesyncd.service - Network Time Synchronization
   Loaded: loaded (/lib/systemd/system/systemd-timesyncd.service; enabled; vendor preset: enabled)
  Drop-In: /usr/lib/systemd/system/systemd-timesyncd.service.d
           └─disable-with-time-daemon.conf
   Active: active (running) since Wed 2019-07-31 14:21:37 EDT; 6s ago
     Docs: man:systemd-timesyncd.service(8)
 Main PID: 1681 (systemd-timesyn)
   Status: "Synchronized to time server for the first time 96.245.170.99:123 (0.debian.pool.ntp.org)."
    Tasks: 2 (limit: 1168)
   Memory: 1.3M
   CGroup: /system.slice/systemd-timesyncd.service
           └─1681 /lib/systemd/systemd-timesyncd

We can use timedatectl to print out systemd’s current understanding of the time:

timedatectl

Output
               Local time: Wed 2019-07-31 14:22:15 EDT
           Universal time: Wed 2019-07-31 18:22:15 UTC
                 RTC time: n/a
                Time zone: America/New_York (EDT, -0400)
System clock synchronized: yes
              NTP service: active
          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 means that the time has been successfully synced, and NTP service: active means that timesyncd is enabled and running.

Conclusion

In this article we’ve shown how to view the system time, change time zones, work with ntpd, and switch to systemd’s timesyncd service. If you have more sophisticated timekeeping needs than what we’ve covered here, you might refer to 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.