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| <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
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| <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
| |
| <refentry id="systemd-timesyncd.service" conditional='ENABLE_TIMESYNCD'> |
| |
| <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>. |
| At the minimum, it will be set to the systemd build date. It is used to ensure that the system clock |
| remains roughly monotonic across reboots, in case no local RTC is available.</para> |
| </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> |
| </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> |