NAME

       systemd-timesyncd.service, systemd-timesyncd - Network Time Synchronization

SYNOPSIS

       systemd-timesyncd.service

       /usr/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.

           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.

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)