1 <?xml version='
1.0'
?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
6 <refentry id=
"timesyncd.conf" conditional='ENABLE_TIMESYNCD'
7 xmlns:
xi=
"http://www.w3.org/2001/XInclude">
9 <title>timesyncd.conf
</title>
10 <productname>systemd
</productname>
14 <refentrytitle>timesyncd.conf
</refentrytitle>
15 <manvolnum>5</manvolnum>
19 <refname>timesyncd.conf
</refname>
20 <refname>timesyncd.conf.d
</refname>
21 <refpurpose>Network Time Synchronization configuration files
</refpurpose>
26 <member><filename>/etc/systemd/timesyncd.conf
</filename></member>
27 <member><filename>/etc/systemd/timesyncd.conf.d/*.conf
</filename></member>
28 <member><filename>/run/systemd/timesyncd.conf.d/*.conf
</filename></member>
29 <member><filename>/usr/lib/systemd/timesyncd.conf.d/*.conf
</filename></member>
34 <title>Description
</title>
36 <para>These configuration files control NTP network time synchronization. See
37 <citerefentry><refentrytitle>systemd.syntax
</refentrytitle><manvolnum>7</manvolnum></citerefentry>
38 for a general description of the syntax.
</para>
41 <xi:include href=
"standard-conf.xml" xpointer=
"main-conf" />
44 <title>Options
</title>
46 <para>The following settings are configured in the [Time] section:
</para>
48 <variablelist class='network-directives'
>
51 <term><varname>NTP=
</varname></term>
52 <listitem><para>A space-separated list of NTP server host names or IP addresses. During runtime this
53 list is combined with any per-interface NTP servers acquired from
54 <citerefentry><refentrytitle>systemd-networkd.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
55 <command>systemd-timesyncd
</command> will contact all configured system or per-interface servers in
56 turn, until one responds. When the empty string is assigned, the list of NTP servers is reset, and
57 all prior assignments will have no effect. This setting defaults to an empty list.
</para>
59 <xi:include href=
"version-info.xml" xpointer=
"v216"/></listitem>
63 <term><varname>FallbackNTP=
</varname></term>
64 <listitem><para>A space-separated list of NTP server host names or IP addresses to be used as the
65 fallback NTP servers. Any per-interface NTP servers obtained from
66 <citerefentry><refentrytitle>systemd-networkd.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
67 take precedence over this setting, as do any servers set via
<varname>NTP=
</varname> above. This
68 setting is hence only relevant if no other NTP server information is known. When the empty string is
69 assigned, the list of NTP servers is reset, and all prior assignments will have no effect. If this
70 option is not given, a compiled-in list of NTP servers is used.
</para>
72 <xi:include href=
"version-info.xml" xpointer=
"v216"/></listitem>
76 <term><varname>RootDistanceMaxSec=
</varname></term>
77 <listitem><para>Maximum acceptable root distance, i.e. the maximum estimated time required for a
78 packet to travel to the server we are connected to from the server with the reference clock. If
79 the current server does not satisfy this limit,
<command>systemd-timesyncd
</command> will switch
80 to a different server.
</para>
82 <para>Takes a time span value. The default unit is seconds, but other units may be specified, see
83 <citerefentry><refentrytitle>systemd.time
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
84 Defaults to
5 seconds.
</para>
86 <xi:include href=
"version-info.xml" xpointer=
"v236"/></listitem>
90 <term><varname>PollIntervalMinSec=
</varname></term>
91 <term><varname>PollIntervalMaxSec=
</varname></term>
92 <listitem><para>The minimum and maximum poll intervals for NTP messages. Polling starts at the
93 minimum poll interval, and is adjusted within the specified limits in response to received packets.
96 <para>Each setting takes a time span value. The default unit is seconds, but other units may be
98 <citerefentry><refentrytitle>systemd.time
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
99 <varname>PollIntervalMinSec=
</varname> defaults to
32 seconds and must not be smaller than
100 16 seconds.
<varname>PollIntervalMaxSec=
</varname> defaults to
34 min
8 s (
2048 seconds) and must be
101 larger than
<varname>PollIntervalMinSec=
</varname>.
</para>
103 <xi:include href=
"version-info.xml" xpointer=
"v236"/></listitem>
107 <term><varname>ConnectionRetrySec=
</varname></term>
108 <listitem><para>Specifies the minimum delay before subsequent attempts to contact a new NTP server
111 <para>Takes a time span value. The default unit is seconds, but other units may be specified, see
112 <citerefentry><refentrytitle>systemd.time
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
113 Defaults to
30 seconds and must not be smaller than
1 second.
</para>
115 <xi:include href=
"version-info.xml" xpointer=
"v248"/></listitem>
119 <term><varname>SaveIntervalSec=
</varname></term>
120 <listitem><para>The interval at which the current time is periodically saved to disk, in the absence
121 of any recent synchronisation from an NTP server. This is especially useful for offline systems
122 with no local RTC, as it will guarantee that the system clock remains roughly monotonic across
125 <para>Takes a time interval value. The default unit is seconds, but other units may be specified, see
126 <citerefentry><refentrytitle>systemd.time
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
127 Defaults to
60 seconds.
</para>
129 <xi:include href=
"version-info.xml" xpointer=
"v250"/></listitem>
136 <title>See Also
</title>
137 <para><simplelist type=
"inline">
138 <member><citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
139 <member><citerefentry><refentrytitle>systemd-timesyncd.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
140 <member><citerefentry><refentrytitle>systemd-networkd.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>