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# systemd-timesyncd

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From ArchWiki

Related articles

- systemd-networkd
- systemd
- System time

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 every 60 seconds), 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.

## Configuration

When starting, systemd-timesyncd will read the configuration file from `/etc/systemd/timesyncd.conf`, which looks like this:

    /etc/systemd/timesyncd.conf

    [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. Alternatively, you can use a configuration snippet in `/etc/systemd/timesyncd.conf.d/*.conf`, see timesyncd.conf(5).

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):

    /etc/systemd/timesyncd.conf or /etc/systemd/timesyncd.conf.d/local.conf

    [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

To verify your configuration:

    $ timedatectl show-timesync --all

    LinkNTPServers=
    SystemNTPServers=
    FallbackNTPServers=0.arch.pool.ntp.org 1.arch.pool.ntp.org 2.arch.pool.ntp.org 3.arch.pool.ntp.org
    ServerName=0.arch.pool.ntp.org
    ServerAddress=103.47.76.177
    RootDistanceMaxUSec=5s
    PollIntervalMinUSec=32s
    PollIntervalMaxUSec=34min 8s
    PollIntervalUSec=1min 4s
    NTPMessage={ Leap=0, Version=4, Mode=4, Stratum=2, Precision=-21, RootDelay=177.398ms, RootDispersion=142.196ms, Reference=C342F10A, OriginateTimestamp=Mon 2018-07-16 13:53:43 +08, ReceiveTimestamp=Mon 2018-07-16 13:53:43 +08, TransmitTimestamp=Mon 2018-07-16 13:53:43 +08, DestinationTimestamp=Mon 2018-07-16 13:53:43 +08, Ignored=no PacketCount=1, Jitter=0 }
    Frequency=22520548

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.conf` will 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.

Note:

- The service writes to a local file `/var/lib/systemd/timesync/clock` with every synchronization and every 60 seconds. This location is hard-coded and cannot be changed.
- This writing may be problematic for running off read-only root partition or trying to minimize writes to an SD card.
- The number of writes can be minimized with a configuration like `PollIntervalMinSec=1d` and `SaveIntervalSec=infinity`.

## Usage

### Enable and start

To enable and start it, simply run:

    # timedatectl set-ntp true

Alternatively (e.g. when running in chroot), start/enable `systemd-timesyncd.service`.

### Check service

The synchronization process might be noticeably slow. This is expected, one should wait a while before determining there is a problem. 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)
    System clock synchronized: yes
                  NTP service: active
              RTC in local TZ: no

### Check verbose

To see verbose service information, use:

    $ timedatectl timesync-status

           Server: 103.47.76.177 (0.arch.pool.ntp.org)
    Poll interval: 2min 8s (min: 32s; max 34min 8s)
             Leap: normal
          Version: 4
          Stratum: 2
        Reference: C342F10A
        Precision: 1us (-21)
    Root distance: 231.856ms (max: 5s)
           Offset: -19.428ms
            Delay: 36.717ms
           Jitter: 7.343ms
     Packet count: 2
        Frequency: +267.747ppm

### View non default config

To see the non default configuration options set and files from which those options are being derived, use:

    $ systemd-analyze cat-config systemd/timesyncd.conf --tldr

    # /etc/systemd/timesyncd.conf
    [Time]

    # /etc/systemd/timesyncd.conf.d/local.conf
    [Time]
    NTP=0.nl.pool.ntp.org 1.nl.pool.ntp.org 2.nl.pool.ntp.org 3.nl.pool.ntp.org
    RootDistanceMaxSec=0.1
    PollIntervalMinSec=1d
    PollIntervalMaxSec=4w
    SaveIntervalSec=infinity

### View log

To view the last 24 hours of logged events, use:

    # journalctl -u systemd-timesyncd --no-hostname --since "1 day ago"

    Jan 19 15:14:20 systemd[1]: Stopping Network Time Synchronization...
    Jan 19 15:14:20 systemd[1]: systemd-timesyncd.service: Deactivated successfully.
    Jan 19 15:14:20 systemd[1]: Stopped Network Time Synchronization.
    Jan 19 15:14:20 systemd[1]: Starting Network Time Synchronization...
    Jan 19 15:14:20 systemd[1]: Started Network Time Synchronization.
    Jan 19 15:14:20 systemd-timesyncd[1023]: Contacted time server 178.215.228.24:123 (0.nl.pool.ntp.org).
    Jan 19 15:14:20 systemd-timesyncd[1023]: Initial clock synchronization to Fri 2024-01-19 15:14:20.393865 CET.

## See also

- Forum: systemd-timesyncd is not syncing time
- Forum: Using systemd-timesync instead of NTP
- Source code of timesyncd
- systemd-timesyncd(8)
- timesyncd.conf(5)

Category:

- Network Time Protocol