SYSTEMD-TI...D.SERVICE(8) systemd-timesyncd.service SYSTEMD-TI...D.SERVICE(8)
NAME
systemd-timesyncd.service, systemd-timesyncd - Network Time
Synchronization
SYNOPSIS
systemd-timesyncd.service
/usr/lib/systemd/systemd-timesyncd
DESCRIPTION
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.
FILES
/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.
SEE ALSO
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)
systemd 257.13 SYSTEMD-TI...D.SERVICE(8)
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