<para><filename>systemd-timedated</filename> is a system service
that may be used as a mechanism to change the system clock and
- timezone, as well as to enable/disable NTP time synchronization.
+ timezone, as well as to enable/disable network time synchronization.
<filename>systemd-timedated</filename> is automatically activated
on request and terminates itself when it is unused.</para>
</refsect1>
<refsect1>
- <title>Environment</title>
-
- <variablelist class='environment-variables'>
- <varlistentry>
- <term><varname>$SYSTEMD_TIMEDATED_NTP_SERVICES</varname></term>
-
- <listitem><para>Colon-separated list of unit names of NTP client services.
- If not set, then
- <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
- is used. See the entries of NTP related commands of
- <citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- for details about this.</para>
-
- <para>Example:
- <programlisting>SYSTEMD_TIMEDATED_NTP_SERVICES=ntpd.service:chronyd.service:systemd-timesyncd.service</programlisting>
- </para></listitem>
- </varlistentry>
- </variablelist>
+ <title>List of network time synchronization services</title>
+
+ <para><command>systemd-timesyncd</command> will look for files with a <literal>.list</literal> extension
+ in <filename>ntp-units.d/</filename> directories. Each file is parsed as a list of unit names, one per
+ line. Empty lines and lines with comments (<literal>#</literal>) are ignored. Files are read from
+ <filename>/usr/lib/systemd/ntp-units.d/</filename> and the corresponding directories under
+ <filename>/etc/</filename>, <filename>/run/</filename>, <filename>/usr/local/lib/</filename>. Files in
+ <filename>/etc/</filename> override files with the same name in <filename>/run/</filename>,
+ <filename>/usr/local/lib/</filename>, and <filename>/usr/lib/</filename>. Files in
+ <filename>/run/</filename> override files with the same name under <filename>/usr/</filename>. Packages
+ should install their configuration files in <filename>/usr/lib/</filename> (distribution packages) or
+ <filename>/usr/local/lib/</filename> (local installs).</para>
+
+ <example>
+ <title><filename>ntp-units.d/</filename> entry for <command>systemd-timesyncd</command></title>
+ <programlisting># /usr/lib/systemd/ntp-units.d/80-systemd-timesync.list
+systemd-timesyncd.service
+</programlisting>
+ </example>
+
+ <para>If the environment variable <varname>$SYSTEMD_TIMEDATED_NTP_SERVICES</varname> is set,
+ <command>systemd-timesyncd</command> will parse the contents of that variable as a colon-separated list
+ of unit names. When set, this variable overrides the file-based list described above.</para>
+
+ <example>
+ <title>An override that specifies that <command>chronyd</command> should be used if available</title>
+ <programlisting>SYSTEMD_TIMEDATED_NTP_SERVICES=chronyd.service:systemd-timesyncd.service</programlisting>
+ </example>
</refsect1>
+
<refsect1>
<title>See Also</title>
<para>