man/systemd-timesyncd.service.xml

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