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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2014 Kay Sievers
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="systemd-timesyncd.service" conditional='ENABLE_TIMESYNCD'>
<refentryinfo>
<title>systemd-timesyncd.service</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Kay</firstname>
<surname>Sievers</surname>
<email>kay@vrfy.org</email>
</author>
</authorgroup>
</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>
</refsect1>
<refsect1>
<title>Files</title>
<variablelist>
<varlistentry>
<term><filename>/var/lib/systemd/clock</filename></term>
<listitem>
<para>This file contains the timestamp of the last successful
synchronization.</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>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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