man/systemd-timesyncd.service.xml

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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   Copyright © 2014 Kay Sievers
   9 -->
  10
  11 <refentry id="systemd-timesyncd.service" conditional='ENABLE_TIMESYNCD'>
  12
  13   <refentryinfo>
  14     <title>systemd-timesyncd.service</title>
  15     <productname>systemd</productname>
  16
  17     <authorgroup>
  18       <author>
  19         <contrib>Developer</contrib>
  20         <firstname>Kay</firstname>
  21         <surname>Sievers</surname>
  22         <email>kay@vrfy.org</email>
  23       </author>
  24     </authorgroup>
  25   </refentryinfo>
  26
  27   <refmeta>
  28     <refentrytitle>systemd-timesyncd.service</refentrytitle>
  29     <manvolnum>8</manvolnum>
  30   </refmeta>
  31
  32   <refnamediv>
  33     <refname>systemd-timesyncd.service</refname>
  34     <refname>systemd-timesyncd</refname>
  35     <refpurpose>Network Time Synchronization</refpurpose>
  36   </refnamediv>
  37
  38   <refsynopsisdiv>
  39     <para><filename>systemd-timesyncd.service</filename></para>
  40     <para><filename>/usr/lib/systemd/systemd-timesyncd</filename></para>
  41   </refsynopsisdiv>
  42
  43   <refsect1>
  44     <title>Description</title>
  45
  46     <para><filename>systemd-timesyncd</filename> is a system service
  47     that may be used to synchronize the local system clock with a
  48     remote Network Time Protocol server. It also saves the local time
  49     to disk every time the clock has been synchronized and uses this
  50     to possibly advance the system realtime clock on subsequent
  51     reboots to ensure it monotonically advances even if the system
  52     lacks a battery-buffered RTC chip.</para>
  53
  54     <para>The <filename>systemd-timesyncd</filename> service
  55     specifically implements only SNTP. This minimalistic
  56     service will set the system clock for large offsets or
  57     slowly adjust it for smaller deltas. More complex use
  58     cases are not covered by <filename>systemd-timesyncd</filename>.</para>
  59
  60     <para>The NTP servers contacted are determined from the global
  61     settings in
  62     <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  63     the per-link static settings in <filename>.network</filename>
  64     files, and the per-link dynamic settings received over DHCP. See
  65     <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  66     for more details.</para>
  67
  68     <para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
  69     <command>set-ntp</command> command may be used to enable and
  70     start, or disable and stop this service.</para>
  71
  72     <para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
  73     <command>timesync-status</command> or <command>show-timesync</command> command can be used to show the
  74     current status of this service.</para>
  75   </refsect1>
  76
  77   <refsect1>
  78     <title>Files</title>
  79
  80     <variablelist>
  81       <varlistentry>
  82         <term><filename>/var/lib/systemd/timesync/clock</filename></term>
  83
  84         <listitem>
  85           <para>The modification time of this file indicates the timestamp of the last successful
  86           synchronization (or at least the systemd build date, in case synchronization was not
  87           possible).</para>
  88         </listitem>
  89       </varlistentry>
  90
  91       <varlistentry>
  92         <term><filename>/run/systemd/timesync/synchronized</filename></term>
  93
  94         <listitem>
  95           <para>A file that is touched on each successful synchronization, to assist
  96           <filename>systemd-time-wait-sync</filename> and other applications to detecting synchronization
  97           events.</para>
  98         </listitem>
  99
 100       </varlistentry>
 101     </variablelist>
 102   </refsect1>
 103
 104   <refsect1>
 105     <title>See Also</title>
 106     <para>
 107       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 108       <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 109       <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 110       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 111       <citerefentry><refentrytitle>systemd-time-wait-sync.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 112       <citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 113       <citerefentry><refentrytitle>localtime</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 114       <citerefentry project='man-pages'><refentrytitle>hwclock</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 115     </para>
 116   </refsect1>
 117
 118 </refentry>