man/systemd-timesyncd.service.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="systemd-timesyncd.service" conditional='ENABLE_TIMESYNCD'>
   7
   8   <refentryinfo>
   9     <title>systemd-timesyncd.service</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd-timesyncd.service</refentrytitle>
  15     <manvolnum>8</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>systemd-timesyncd.service</refname>
  20     <refname>systemd-timesyncd</refname>
  21     <refpurpose>Network Time Synchronization</refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <para><filename>systemd-timesyncd.service</filename></para>
  26     <para><filename>/usr/lib/systemd/systemd-timesyncd</filename></para>
  27   </refsynopsisdiv>
  28
  29   <refsect1>
  30     <title>Description</title>
  31
  32     <para><filename>systemd-timesyncd</filename> is a system service
  33     that may be used to synchronize the local system clock with a
  34     remote Network Time Protocol server. It also saves the local time
  35     to disk every time the clock has been synchronized and uses this
  36     to possibly advance the system realtime clock on subsequent
  37     reboots to ensure it monotonically advances even if the system
  38     lacks a battery-buffered RTC chip.</para>
  39
  40     <para>The <filename>systemd-timesyncd</filename> service
  41     specifically implements only SNTP. This minimalistic
  42     service will set the system clock for large offsets or
  43     slowly adjust it for smaller deltas. More complex use
  44     cases are not covered by <filename>systemd-timesyncd</filename>.</para>
  45
  46     <para>The NTP servers contacted are determined from the global
  47     settings in
  48     <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  49     the per-link static settings in <filename>.network</filename>
  50     files, and the per-link dynamic settings received over DHCP. See
  51     <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  52     for more details.</para>
  53
  54     <para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
  55     <command>set-ntp</command> command may be used to enable and
  56     start, or disable and stop this service.</para>
  57
  58     <para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
  59     <command>timesync-status</command> or <command>show-timesync</command> command can be used to show the
  60     current status of this service.</para>
  61   </refsect1>
  62
  63   <refsect1>
  64     <title>Files</title>
  65
  66     <variablelist>
  67       <varlistentry>
  68         <term><filename>/var/lib/systemd/timesync/clock</filename></term>
  69
  70         <listitem>
  71           <para>The modification time of this file indicates the timestamp of the last successful
  72           synchronization (or at least the systemd build date, in case synchronization was not
  73           possible).</para>
  74         </listitem>
  75       </varlistentry>
  76
  77       <varlistentry>
  78         <term><filename>/run/systemd/timesync/synchronized</filename></term>
  79
  80         <listitem>
  81           <para>A file that is touched on each successful synchronization, to assist
  82           <filename>systemd-time-wait-sync</filename> and other applications to detecting synchronization
  83           events.</para>
  84         </listitem>
  85
  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>systemd-time-wait-sync.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  98       <citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  99       <citerefentry><refentrytitle>localtime</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 100       <citerefentry project='man-pages'><refentrytitle>hwclock</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 101     </para>
 102   </refsect1>
 103
 104 </refentry>