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 16.04 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.
Before starting this tutorial, you will need an Ubuntu 16.04 server with a non-root, sudo-enabled user, as described in this Ubuntu 16.04 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:
Wed Apr 26 17:44:38 UTC 2017
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
timedatectlcommand 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
timedatectl to make this change:
- sudo timedatectl set-timezone America/New_York
You can verify your changes by running
Wed Apr 26 13:55:45 EDT 2017
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 server 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:
Local time: Wed 2017-04-26 17:20:07 UTC Universal time: Wed 2017-04-26 17:20:07 UTC RTC time: Wed 2017-04-26 17:20:07 Time zone: Etc/UTC (UTC, +0000) Network time on: yes NTP synchronized: 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.
Network time on: yes means that timesyncd is enabled, and
NTP synchronized: yes indicates that the time has been successfully synced.
If timesyncd isn’t enabled, turn it on with timedatectl:
- sudo timedatectl set-ntp on
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
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:
Network time on: no in the output. This means
timesyncd has been stopped. We can now install the
ntp package with
- sudo apt-get install ntp
ntpd will be started automatically after install. You can query ntpd for status information to verify that everything is working:
- sudo 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 -makaki.miuku.ne 188.8.131.52 2 u 45 64 3 248.007 -0.489 1.137 -184.108.40.206 220.127.116.11 3 u 43 64 3 90.551 4.316 0.550 +static-ip-85-25 18.104.22.168 2 u 42 64 3 80.044 -2.829 0.900 +zepto.mcl.gg 22.214.171.124 2 u 40 64 3 83.331 -0.385 0.391
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.
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.