SYSTEMD-TIMESYNCD.SERVICE(8systemd-timesyncd.serviSYSTEMD-TIMESYNCD.SERVICE(8)
NAME
systemd-timesyncd.service, systemd-timesyncd - Network Time
Synchronization
SYNOPSIS
systemd-timesyncd.service
/lib/systemd/systemd-timesyncd
DESCRIPTION
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.
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).
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.
/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.
/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.
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 252 SYSTEMD-TIMESYNCD.SERVICE(8)
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