man/systemd-timesyncd.service.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
   9
  10   Copyright 2014 Kay Sievers
  11 -->
  12
  13 <refentry id="systemd-timesyncd.service" conditional='ENABLE_TIMESYNCD'>
  14
  15   <refentryinfo>
  16     <title>systemd-timesyncd.service</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>Developer</contrib>
  22         <firstname>Kay</firstname>
  23         <surname>Sievers</surname>
  24         <email>kay@vrfy.org</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>systemd-timesyncd.service</refentrytitle>
  31     <manvolnum>8</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>systemd-timesyncd.service</refname>
  36     <refname>systemd-timesyncd</refname>
  37     <refpurpose>Network Time Synchronization</refpurpose>
  38   </refnamediv>
  39
  40   <refsynopsisdiv>
  41     <para><filename>systemd-timesyncd.service</filename></para>
  42     <para><filename>/usr/lib/systemd/systemd-timesyncd</filename></para>
  43   </refsynopsisdiv>
  44
  45   <refsect1>
  46     <title>Description</title>
  47
  48     <para><filename>systemd-timesyncd</filename> is a system service
  49     that may be used to synchronize the local system clock with a
  50     remote Network Time Protocol server. It also saves the local time
  51     to disk every time the clock has been synchronized and uses this
  52     to possibly advance the system realtime clock on subsequent
  53     reboots to ensure it monotonically advances even if the system
  54     lacks a battery-buffered RTC chip.</para>
  55
  56     <para>The <filename>systemd-timesyncd</filename> service
  57     specifically implements only SNTP. This minimalistic
  58     service will set the system clock for large offsets or
  59     slowly adjust it for smaller deltas. More complex use
  60     cases are not covered by <filename>systemd-timesyncd</filename>.</para>
  61
  62     <para>The NTP servers contacted are determined from the global
  63     settings in
  64     <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  65     the per-link static settings in <filename>.network</filename>
  66     files, and the per-link dynamic settings received over DHCP. See
  67     <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  68     for more details.</para>
  69
  70     <para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
  71     <command>set-ntp</command> command may be used to enable and
  72     start, or disable and stop this service.</para>
  73   </refsect1>
  74
  75   <refsect1>
  76     <title>Files</title>
  77
  78     <variablelist>
  79       <varlistentry>
  80         <term><filename>/var/lib/systemd/timesync/clock</filename></term>
  81
  82         <listitem>
  83           <para>This file contains the timestamp of the last successful
  84           synchronization.</para>
  85         </listitem>
  86       </varlistentry>
  87     </variablelist>
  88   </refsect1>
  89
  90   <refsect1>
  91     <title>See Also</title>
  92     <para>
  93       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  94       <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  95       <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  96       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  97       <citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  98       <citerefentry><refentrytitle>localtime</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  99       <citerefentry project='man-pages'><refentrytitle>hwclock</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 100     </para>
 101   </refsect1>
 102
 103 </refentry>