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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="systemd-timesyncd.service" conditional='ENABLE_TIMESYNCD'>
<refentryinfo>
<title>systemd-timesyncd.service</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-timesyncd.service</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-timesyncd.service</refname>
<refname>systemd-timesyncd</refname>
<refpurpose>Network Time Synchronization</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>systemd-timesyncd.service</filename></para>
<para><filename>/usr/lib/systemd/systemd-timesyncd</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-timesyncd</filename> is a system service
that may be used to synchronize the local system clock with a
remote Network Time Protocol 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 monotonically advances even if the system
lacks a battery-buffered RTC chip.</para>
<para>The <filename>systemd-timesyncd</filename> service
specifically implements only SNTP. This minimalistic
service will set the system clock for large offsets or
slowly adjust it for smaller deltas. More complex use
cases are not covered by <filename>systemd-timesyncd</filename>.</para>
<para>The NTP servers contacted are determined from the global
settings in
<citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
the per-link static settings in <filename>.network</filename>
files, and the per-link dynamic settings received over DHCP. See
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more details.</para>
<para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
<command>set-ntp</command> command may be used to enable and
start, or disable and stop this service.</para>
<para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
<command>timesync-status</command> or <command>show-timesync</command> command can be used to show the
current status of this service.</para>
</refsect1>
<refsect1>
<title>Files</title>
<variablelist>
<varlistentry>
<term><filename>/var/lib/systemd/timesync/clock</filename></term>
<listitem>
<para>The modification time of this file indicates the timestamp of the last successful
synchronization (or at least the systemd build date, in case synchronization was not
possible).</para>
</listitem>
</varlistentry>
<varlistentry>
<term><filename>/run/systemd/timesync/synchronized</filename></term>
<listitem>
<para>A file that is touched on each successful synchronization, to assist
<filename>systemd-time-wait-sync</filename> and other applications to detecting synchronization
events.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-time-wait-sync.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>localtime</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>hwclock</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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