mirror of
https://github.com/systemd/systemd.git
synced 2024-11-23 18:23:32 +08:00
aefdc1124f
As I noticed a lot of missing information when trying to implement checking
for missing info. I reimplemented the version information script to be more
robust, and here is the result.
Follow up to ec07c3c80b
135 lines
6.7 KiB
XML
135 lines
6.7 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
|
||
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
||
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
|
||
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
|
||
|
||
<refentry id="systemd-timesyncd.service" conditional='ENABLE_TIMESYNCD'
|
||
xmlns:xi="http://www.w3.org/2001/XInclude">
|
||
|
||
<refentryinfo>
|
||
<title>systemd-timesyncd.service</title>
|
||
<productname>systemd</productname>
|
||
</refentryinfo>
|
||
|
||
<refmeta>
|
||
<refentrytitle>systemd-timesyncd.service</refentrytitle>
|
||
<manvolnum>8</manvolnum>
|
||
</refmeta>
|
||
|
||
<refnamediv>
|
||
<refname>systemd-timesyncd.service</refname>
|
||
<refname>systemd-timesyncd</refname>
|
||
<refpurpose>Network Time Synchronization</refpurpose>
|
||
</refnamediv>
|
||
|
||
<refsynopsisdiv>
|
||
<para><filename>systemd-timesyncd.service</filename></para>
|
||
<para><filename>/usr/lib/systemd/systemd-timesyncd</filename></para>
|
||
</refsynopsisdiv>
|
||
|
||
<refsect1>
|
||
<title>Description</title>
|
||
|
||
<para><filename>systemd-timesyncd</filename> is a system service that may be used to synchronize the
|
||
local system clock with a remote Network Time Protocol (NTP) server. It also saves the local time to disk
|
||
every time the clock has been synchronized and uses this to possibly advance the system realtime clock on
|
||
subsequent reboots to ensure it (roughly) monotonically advances even if the system lacks a
|
||
battery-buffered RTC chip.</para>
|
||
|
||
<para>The <filename>systemd-timesyncd</filename> service implements SNTP only. This minimalistic service
|
||
will step the system clock for large offsets or slowly adjust it for smaller deltas. Complex use cases
|
||
that require full NTP support (and where SNTP is not sufficient) are not covered by
|
||
<filename>systemd-timesyncd</filename>.</para>
|
||
|
||
<para>The NTP servers contacted are determined from the global settings in
|
||
<citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, the
|
||
per-link static settings in <filename>.network</filename> files, and the per-link dynamic settings
|
||
received over DHCP. See
|
||
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
|
||
further details.</para>
|
||
|
||
<para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
|
||
<command>set-ntp</command> command may be used to enable and start, or disable and stop this
|
||
service.</para>
|
||
|
||
<para><citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
|
||
<command>timesync-status</command> or <command>show-timesync</command> command can be used to show the
|
||
current status of this service.</para>
|
||
|
||
<para><filename>systemd-timesyncd</filename> initialization delays the start of units that are ordered
|
||
after <filename>time-set.target</filename> (see
|
||
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
|
||
details) until the local time has been updated from <filename>/var/lib/systemd/timesync/clock</filename>
|
||
(see below) in order to make it roughly monotonic. It does not delay other units until synchronization
|
||
with an accurate reference time sources has been reached. Use
|
||
<citerefentry><refentrytitle>systemd-time-wait-sync.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
|
||
to achieve that, which will delay start of units that are ordered after
|
||
<filename>time-sync.target</filename> until synchronization to an accurate reference clock is
|
||
reached.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Files</title>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term><filename>/var/lib/systemd/timesync/clock</filename></term>
|
||
|
||
<listitem>
|
||
<para>The modification time ("mtime") of this file is updated on each successful NTP
|
||
synchronization or after each <varname>SaveIntervalSec=</varname> time interval, as specified in
|
||
<citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
|
||
|
||
<para>When initializing, the local clock is advanced to the modification time of this file (if the
|
||
file timestamp is in the past this adjustment is not made). If the file does not exist yet, the
|
||
clock is instead advanced to the modification time of <filename>/usr/lib/clock-epoch</filename> –
|
||
if it exists – or to a time derived from the source tree at build time. This mechanism is used to
|
||
ensure that the system clock remains somewhat reasonably initialized and roughly monotonic across
|
||
reboots, in case no battery-buffered local RTC is available.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v219"/>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><filename>/usr/lib/clock-epoch</filename></term>
|
||
|
||
<listitem><para>The modification time ("mtime") of this file is used for advancing the system clock
|
||
in case <filename>/var/lib/systemd/timesync/clock</filename> does not exist yet, see
|
||
above.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><filename>/run/systemd/timesync/synchronized</filename></term>
|
||
|
||
<listitem>
|
||
<para>A file that is touched on each successful synchronization, to assist
|
||
<filename>systemd-time-wait-sync</filename> and other applications to detecting synchronization
|
||
with accurate reference clocks.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v239"/>
|
||
</listitem>
|
||
|
||
</varlistentry>
|
||
</variablelist>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>See Also</title>
|
||
<para>
|
||
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>systemd-time-wait-sync.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>localtime</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
||
<citerefentry project='man-pages'><refentrytitle>hwclock</refentrytitle><manvolnum>8</manvolnum></citerefentry>
|
||
</para>
|
||
</refsect1>
|
||
|
||
</refentry>
|