From the systemd mailing list:
- systemd-timesyncd is a daemon that has been added for synchronizing the system clock across the network. It implements an SNTP client. In contrast to NTP implementations such as chrony or the NTP reference server this only implements a client side, and does not bother with the full NTP complexity, focusing only on querying time from one remote server and synchronizing the local clock to it. Unless you intend to serve NTP to networked clients or want to connect to local hardware clocks this simple NTP client should be more than appropriate for most installations. The daemon runs with minimal privileges, and has been hooked up with networkd to only operate when network connectivity is available. The daemon saves the current clock to disk every time a new NTP sync has been acquired, and uses this to possibly correct the system clock early at bootup, in order to accommodate for systems that lack an RTC such as the Raspberry Pi and embedded devices, and make sure that time monotonically progresses on these systems, even if it is not always correct. To make use of this daemon a new system user and group "systemd-timesync" needs to be created on installation of systemd.
The systemd-timesyncd service is available with. To start and enable it, simply run:
# timedatectl set-ntp true
To check the service status, use
$ timedatectl status
Local time: Thu 2015-07-09 18:21:33 CEST Universal time: Thu 2015-07-09 16:21:33 UTC RTC time: Thu 2015-07-09 16:21:33 Time zone: Europe/Amsterdam (CEST, +0200) Network time on: yes NTP synchronized: yes RTC in local TZ: no
When starting, systemd-timesyncd will read the configuration file from
/etc/systemd/timesyncd.conf, which looks like this:
[Time] #NTP= #FallbackNTP=0.arch.pool.ntp.org 1.arch.pool.ntp.org 2.arch.pool.ntp.org 3.arch.pool.ntp.org
To add time servers or change the provided ones, uncomment the relevant line and list their host name or IP separated by a space. For example, you can use any servers provided by the NTP pool project or use the default Arch ones (also provided by the NTP pool project):
[Time] NTP=0.arch.pool.ntp.org 1.arch.pool.ntp.org 2.arch.pool.ntp.org 3.arch.pool.ntp.org FallbackNTP=0.pool.ntp.org 1.pool.ntp.org 0.fr.pool.ntp.org
Further to the daemon configuration, NTP servers may also be provided via a systemd-networkd configuration with a
NTP= option or, dynamically, via a DHCP server.
The NTP server to be used will be determined using the following rules:
- Any per-interface NTP servers obtained from
systemd-networkd.service(8)configuration or via DHCP take precedence.
- The NTP servers defined in
/etc/systemd/timesyncd.confwill be appended to the per-interface list at runtime and the daemon will contact the servers in turn until one is found that responds.
- If no NTP server information is acquired after completing those steps, the NTP server host names or IP addresses defined in
FallbackNTP=will be used.
/var/lib/systemd/clockwith every synchronization. This location is hard-coded and cannot be changed. This may be problematic for running off read-only root partition or trying to minimize writes to an SD card.