systemd-timesyncd - the lightweight NTP client · Linux

systemd-timesyncd is the lightweight NTP client that ships with systemd. It is a smaller alternative to chrony, with fewer features but easier setup. It is the default on Ubuntu desktop and increasingly common on minimal Linux installs.

What it does

Acts as an NTP client.
Adjusts the system clock via slewing.
Supports NTS (Network Time Security) for authenticated time.
Persists the RTC across reboots.

What it does NOT do

It does NOT serve NTP to other hosts.
It does NOT support complex source selection.
It does NOT support authentication via shared keys.
It does NOT support reference clocks.

For a server that needs NTP server functionality or complex configuration, chrony is the right choice.

Configure

/etc/systemd/timesyncd.conf:

[Time]
NTP=time.cloudflare.com ntp1.example.com
FallbackNTP=0.pool.ntp.org 1.pool.ntp.org
RootDistanceMaxSec=5
PollIntervalMinSec=32
PollIntervalMaxSec=2048

Apply:

sudo systemctl restart systemd-timesyncd
timedatectl status

Inspect

timedatectl status

Output:

               Local time: Sun 2026-08-09 14:30:00 UTC
           Universal time: Sun 2026-08-09 14:30:00 UTC
                 RTC time: Sun 2026-08-09 14:30:00
                Time zone: UTC (UTC, +0000)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

Key fields:

Local time: in the system time zone.
Universal time: UTC.
System clock synchronized: yes if NTP is syncing successfully.
NTP service: active if systemd-timesyncd is running.
RTC in local TZ: should be no (RTC should be UTC).

timedatectl timesync-status

Output:

       Server: time.cloudflare.com (162.159.200.1)
Poll interval: 32s (min: 32s; max: 34min 8s)
         Leap: normal
      Version: 4
      Stratum: 3
    Reference: 6A0E80A3
    Precision: 1us (-24s)
Root distance: 24ms (max: 5s)
         Offset: -1.234ms
          Delay: 12.345ms
         Jitter: 0.456ms
 Packet count: 1234

Reading this:

Server: current NTP source.
Offset: difference between system clock and server. <10 ms is good.
Delay: round-trip time to the server.
Jitter: variation in delay. <1 ms is good.
Packet count: total packets exchanged.

NTS support

systemd-timesyncd supports NTS (Network Time Security, RFC 8915) for authenticated time. Configure:

[Time]
NTP=time.cloudflare.com
NTS=time.cloudflare.com

time.cloudflare.com supports NTS. Other public servers may not. NTS provides authentication and encryption for NTP queries, protecting against spoofing.

When to use chrony instead

Use chrony when:

The host is an NTP server for the local network.
The host is on a frequently-disconnected network (laptop).
The host needs complex source selection (e.g. GPS reference clock).
Authentication via shared keys is required.
High accuracy (<1 ms) is needed.

Use systemd-timesyncd when:

The host is a desktop or simple server.
Internet NTP is the only source.
Minimal configuration is preferred.

For new production servers, prefer chrony. For desktop and container images, systemd-timesyncd is sufficient.

Diagnose

timedatectl status
timedatectl timesync-status
journalctl -u systemd-timesyncd -n 50

Common issues:

“System clock synchronized: no”: NTP source is unreachable. Check the network and the configured NTP servers.
Large offset (>1 second): the host clock is far off; NTP is slewing it back. Initial sync may take a few minutes.
“NTP service: inactive”: systemd-timesyncd is not running. Enable and start with systemctl enable --now systemd-timesyncd.