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2dd79846dd
Systems that have an accurate real-time clock may have an initial unsynchronized time that is close enough to the synchronized time that the final adjustment doesn't trigger a waking "clock set" event. Have timesyncd touch a file in its runtime directory as a secondary signal for synchronization. Continue to support the timerfd-based trigger as a sufficient condition when the watchfile is not present. Closes issue #8683
116 lines
4.3 KiB
XML
116 lines
4.3 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2014 Kay Sievers
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-->
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<refentry id="systemd-timesyncd.service" conditional='ENABLE_TIMESYNCD'>
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<refentryinfo>
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<title>systemd-timesyncd.service</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Kay</firstname>
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<surname>Sievers</surname>
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<email>kay@vrfy.org</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-timesyncd.service</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-timesyncd.service</refname>
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<refname>systemd-timesyncd</refname>
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<refpurpose>Network Time Synchronization</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-timesyncd.service</filename></para>
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<para><filename>/usr/lib/systemd/systemd-timesyncd</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-timesyncd</filename> is a system service
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that may be used to synchronize the local system clock with a
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remote Network Time Protocol server. It also saves the local time
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to disk every time the clock has been synchronized and uses this
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to possibly advance the system realtime clock on subsequent
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reboots to ensure it monotonically advances even if the system
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lacks a battery-buffered RTC chip.</para>
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<para>The <filename>systemd-timesyncd</filename> service
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specifically implements only SNTP. This minimalistic
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service will set the system clock for large offsets or
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slowly adjust it for smaller deltas. More complex use
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cases are not covered by <filename>systemd-timesyncd</filename>.</para>
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<para>The NTP servers contacted are determined from the global
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settings in
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<citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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the per-link static settings in <filename>.network</filename>
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files, and the per-link dynamic settings received over DHCP. See
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<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for more details.</para>
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<para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
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<command>set-ntp</command> command may be used to enable and
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start, or disable and stop this service.</para>
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</refsect1>
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<refsect1>
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<title>Files</title>
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<variablelist>
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<varlistentry>
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<term><filename>/var/lib/systemd/timesync/clock</filename></term>
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<listitem>
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<para>The modification time of this file indicates the timestamp of the last successful
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synchronization.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><filename>/run/systemd/timesync/synchronized</filename></term>
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<listitem>
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<para>A file that is touched on each successful synchronization, to assist
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<filename>systemd-time-wait-sync</filename> and other applications to detecting synchronization
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events.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-time-wait-sync.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>localtime</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>hwclock</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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