Ubuntu – Prevent clock from advancing to a system time after Ubuntu Server build time

clockdatertcservertime

I have an Ubuntu Server 18.04.1 LTS in a lab environment where I need to set the date a couple of years back in time (e.g. 2016-04-22). I can set the older date/time without any issues but the OS always resets the date/time to 2018-01-28 15:58 whenever I power the server back on. How can I prevent this?

I found a log message in /var/log/syslog indicating that the OS is switching to the previous build time: systemd[1]: System time before build time, advancing clock.

Best Answer

Try disabling the systemd-timesyncd service:

sudo systemctl disable systemd-timesyncd

You can check if the service is running using:

sudo service systemd-timesyncd status

You can stop the service manually (one time) using:

sudo service systemd-timesyncd stop

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NTP daemons don't want to do a sudden massive jump in system time. For one, it borks the chronology of entries in your log files, system daemons might freak out, etc. What it does instead is "drift" your system clock into place. If you want to check how far off from "the actual time" you are you can query an ntp server:

ntpdate -q pool.ntp.org

NTP works by adjusting the length of a second on your system by a slight bit so that you slowly get the correct time. It can take a while for the drift to happen if your offset is high. What you can do though is force a hard sync once:

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ntpdate pool.ntp.org
service ntp start

Edit: in response to the comments below.

Set this line up in /etc/default/ntpdate

NTPDATE_USE_NTP_CONF=yes

Best Answer

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