<?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+ -->
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="systemd.time">
<para>One can use the <command>timespan</command> command of
<citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
to normalise a textual time span for testing and validation purposes.</para>
+
+ <para>Internally, systemd generally operates with microsecond time granularity, while the default time
+ unit in user-configurable time spans is usually seconds (see above). This disparity becomes visible when
+ comparing the same settings in the (high-level) unit file syntax with the matching (more low-level) D-Bus
+ properties (which are what
+ <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
+ <command>show</command> command displays). The former typically are suffixed with <literal>…Sec</literal>
+ to indicate the default unit of seconds, the latter are typically suffixed with <literal>…USec</literal>
+ to indicate the underlying low-level time unit, even if they both encapsulate the very same
+ settings.</para>
</refsect1>
<refsect1>
<refsect1>
<title>Parsing Timestamps</title>
- <para>When parsing, systemd will accept a similar syntax, but expects no timezone specification, unless it is given
- as the literal string <literal>UTC</literal> (for the UTC timezone), or is specified to be the locally configured
- timezone, or the timezone name in the IANA timezone database format. The complete list of timezones
- supported on your system can be obtained using the <literal>timedatectl list-timezones</literal>
- (see <citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>).
- Using IANA format is recommended over local timezone names, as less prone to errors (eg: with local timezone it's possible to
- specify daylight saving time in winter, while it's incorrect). The weekday specification is optional, but when
- the weekday is specified, it must either be in the abbreviated (<literal>Wed</literal>) or non-abbreviated
- (<literal>Wednesday</literal>) English language form (case does not matter), and is not subject to the locale
- choice of the user. Either the date, or the time part may be omitted, in which case the current date or 00:00:00,
- respectively, is assumed. The seconds component of the time may also be omitted, in which case ":00" is
- assumed. Year numbers may be specified in full or may be abbreviated (omitting the century).</para>
+ <para>When parsing, systemd will accept a similar syntax, but expects no timezone specification, unless
+ it is given as the literal string <literal>UTC</literal> (for the UTC timezone), or is specified to be
+ the locally configured timezone, or the timezone name in the IANA timezone database format. The complete
+ list of timezones supported on your system can be obtained using the <literal>timedatectl
+ list-timezones</literal> (see
+ <citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>). Using
+ IANA format is recommended over local timezone names, as less prone to errors (e.g. with local timezone
+ it's possible to specify daylight saving time in winter, even though that is not correct). The weekday
+ specification is optional, but when the weekday is specified, it must either be in the abbreviated
+ (<literal>Wed</literal>) or non-abbreviated (<literal>Wednesday</literal>) English language form (case
+ does not matter), and is not subject to the locale choice of the user. Either the date, or the time part
+ may be omitted, in which case the current date or 00:00:00, respectively, is assumed. The seconds
+ component of the time may also be omitted, in which case ":00" is assumed. Year numbers may be specified
+ in full or may be abbreviated (omitting the century).</para>
<para>A timestamp is considered invalid if a weekday is specified and the date does not match the specified day of
the week.</para>
<para>Use the <command>calendar</command> command of
<citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry> to validate
and normalize calendar time specifications for testing purposes. The tool also calculates when a specified
- calendar event would elapse next.</para>
+ calendar event would occur next.</para>
</refsect1>
<refsect1>
projects / thirdparty / systemd.git / blobdiff