diff options
Diffstat (limited to '')
| -rw-r--r-- | man/systemd-timesyncd.service.xml | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/man/systemd-timesyncd.service.xml b/man/systemd-timesyncd.service.xml new file mode 100644 index 0000000..45fb6b7 --- /dev/null +++ b/man/systemd-timesyncd.service.xml @@ -0,0 +1,127 @@ +<?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'> + + <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> + </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></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> |