Configure Offline NTP Time Sync on Ubuntu/Debian with systemd-timesyncd

Ubuntu's default time synchronization server is ntp.ubuntu.com, while Debian uses 0.debian.pool.ntp.org; each Linux distribution provides its own official NTP servers. In China these servers may have high latency, but the impact on clock synchronization is minimal.

In environments without internet access, such as corporate intranets or cloud subnets, you must configure time synchronization yourself.

This article shows how to set up time synchronization without building your own NTP server.

Installation

systemd-timesyncd is usually pre‑installed. If it is missing, install it manually: sudo apt install systemd-timesyncd The package conflicts with the traditional ntp package, so only one can be installed at a time.

Configuration

Edit /etc/systemd/timesyncd.conf and set the NTP servers to ones reachable from within China, for example:

[Time]
NTP=ntp7.aliyun.com
NTP=ntp6.aliyun.com

After saving the file, restart the service for the changes to take effect:

sudo systemctl restart systemd-timesyncd.service

If the systemd-timesyncd.service unit is missing, you can restore it with:

sudo dpkg-reconfigure systemd-timesyncd

Verify Synchronization

Use timedatectl status to view detailed synchronization information, for example:

Local time: Tue 2020-09-22 20:06:05 CST
Universal time: Tue 2020-09-22 12:06:05 UTC
RTC time: Tue 2020-09-22 12:06:05
Time zone: Asia/Shanghai (CST, +0800)
System clock synchronized: yes
NTP service: active

Domestic NTP Server List

Some Alibaba Cloud NTP servers that can be used (choose the best with ping):

ntp1.aliyun.com
ntp2.aliyun.com
ntp3.aliyun.com
ntp4.aliyun.com
ntp5.aliyun.com
ntp6.aliyun.com
ntp7.aliyun.com