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SYSTEMD-T....SERVICE(8) systemd-timesyncd.serviceSYSTEMD-T....SERVICE(8)
systemd-timesyncd.service, systemd-timesyncd - Network Time
Synchronization
systemd-timesyncd.service
/usr/lib/systemd/systemd-timesyncd
systemd-timesyncd 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 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.
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.
systemd-timesyncd initialization 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.
/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).
When initializing, the local clock is advanced to the
modification time of this file (if the file timestamp is in
the past this adjustment is not made). If the file does not
exist yet, the clock is instead advanced to the modification
time of /usr/lib/clock-epoch – if it exists – or to a time
derived from the source tree at build time. This mechanism is
used to ensure that the system clock remains somewhat
reasonably initialized and roughly monotonic across reboots,
in case no battery-buffered local RTC is available.
Added in version 219.
/usr/lib/clock-epoch
The modification time ("mtime") of this file is used for
advancing the system clock in case
/var/lib/systemd/timesync/clock does not exist yet, see
above.
Added in version 254.
/run/systemd/timesync/synchronized
A file that is touched on each successful synchronization, to
assist systemd-time-wait-sync and other applications to
detecting synchronization with accurate reference clocks.
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 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) 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
man-pages@man7.org
systemd 257~devel SYSTEMD-T....SERVICE(8)
Pages that refer to this page: timedatectl(1), 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 2024-06-26 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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