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SYSTEMD-T....SERVICE(8) systemd-timesyncd.service SYSTEMD-T....SERVICE(8)
systemd-timesyncd.service, systemd-timesyncd - Network Time
Synchronization
systemd-timesyncd.service
/usr/lib/systemd/systemd-timesyncd
systemd-timesyncd.service is a system service that may be used to
synchronize the local system clock with a remote Network Time
Protocol (NTP) server. It also saves the local time to disk every
time the clock has been synchronized and uses this to possibly
advance the system realtime clock on subsequent reboots to ensure
it (roughly) monotonically advances even if the system lacks a
battery-buffered RTC chip.
The systemd-timesyncd.service service implements SNTP only. This
minimalistic service will step the system clock for large offsets
or slowly adjust it for smaller deltas. Complex use cases that
require full NTP support (and where SNTP is not sufficient) are
not covered by systemd-timesyncd.service.
The NTP servers contacted are determined from the global settings
in timesyncd.conf(5), the per-link static settings in .network
files, and the per-link dynamic settings received over DHCP. See
systemd.network(5) for further details.
timedatectl(1)'s set-ntp command may be used to enable and start,
or disable and stop this service.
timedatectl(1)'s timesync-status or show-timesync command can be
used to show the current status of this service.
Initialization of systemd-timesyncd.service delays the start of
units that are ordered after time-set.target (see
systemd.special(7) for details) until the local time has been
updated from /var/lib/systemd/timesync/clock (see below) in order
to make it roughly monotonic. It does not delay other units until
synchronization with an accurate reference time sources has been
reached. Use systemd-time-wait-sync.service(8) to achieve that,
which will delay start of units that are ordered after
time-sync.target until synchronization to an accurate reference
clock is reached.
systemd and systemd-timesyncd advance the system clock to the
"epoch" (the lowest date above which the system clock time is
assumed to be set correctly). See "System clock epoch" section in
systemd(1) for details. systemd will set the clock when
initializing, but /var/lib/systemd/timesync/clock might not yet be
available at that point. systemd-timesyncd will advance the clock
when it is started and notices that the system clock is before the
modification time of /var/lib/systemd/timesync/clock.
/var/lib/systemd/timesync/clock
The modification time ("mtime") of this file is updated on
each successful NTP synchronization or after each
SaveIntervalSec= time interval, as specified in
timesyncd.conf(5).
If present, the modification time of this file is used for the
epoch by systemd(1) and systemd-timesyncd.service.
Added in version 219.
/run/systemd/timesync/synchronized
A file that is touched on each successful synchronization to
assist systemd-time-wait-sync.service(8) service and other
applications in detecting synchronization to an accurate
reference clock.
Added in version 239.
systemd(1), timesyncd.conf(5), systemd.network(5),
systemd-networkd.service(8), systemd-time-wait-sync.service(8),
systemd.special(7), timedatectl(1), localtime(5), hwclock(8)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 258~rc2 SYSTEMD-T....SERVICE(8)
Pages that refer to this page: systemd(1), timedatectl(1), org.freedesktop.timesync1(5), systemd.network(5), timesyncd.conf(5), systemd.directives(7), systemd.index(7), systemd.special(7), systemd-timedated.service(8), systemd-time-wait-sync.service(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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