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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+ SPDX-License-Identifier: LGPL-2.1+
+-->
+
+<refentry id="systemd.time">
+
+ <refentryinfo>
+ <title>systemd.time</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>systemd.time</refentrytitle>
+ <manvolnum>7</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>systemd.time</refname>
+ <refpurpose>Time and date specifications</refpurpose>
+ </refnamediv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>In systemd, timestamps, time spans, and calendar events are
+ displayed and may be specified in closely related syntaxes.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Displaying Time Spans</title>
+
+ <para>Time spans refer to time durations. On display, systemd will present time spans as a space-separated series
+ of time values each suffixed by a time unit. Example:</para>
+
+ <programlisting>2h 30min</programlisting>
+
+ <para>All specified time values are meant to be added up. The above hence refers to 150 minutes. Display is
+ locale-independent, only English names for the time units are used.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Parsing Time Spans</title>
+
+ <para>When parsing, systemd will accept the same time span syntax.
+ Separating spaces may be omitted. The following time units are
+ understood:</para>
+
+ <itemizedlist>
+ <listitem><para>usec, us, µs</para></listitem>
+ <listitem><para>msec, ms</para></listitem>
+ <listitem><para>seconds, second, sec, s</para></listitem>
+ <listitem><para>minutes, minute, min, m</para></listitem>
+ <listitem><para>hours, hour, hr, h</para></listitem>
+ <listitem><para>days, day, d</para></listitem>
+ <listitem><para>weeks, week, w</para></listitem>
+ <listitem><para>months, month, M (defined as 30.44 days)</para></listitem>
+ <listitem><para>years, year, y (defined as 365.25 days)</para></listitem>
+ </itemizedlist>
+
+ <para>If no time unit is specified, generally seconds are assumed, but some exceptions exist and are marked as
+ such. In a few cases <literal>ns</literal>, <literal>nsec</literal> is accepted too, where the granularity of the
+ time span permits this. Parsing is generally locale-independent, non-English names for the time units are not
+ accepted.</para>
+
+ <para>Examples for valid time span specifications:</para>
+
+ <programlisting>2 h
+2hours
+48hr
+1y 12month
+55s500ms
+300ms20s 5day</programlisting>
+
+ <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>
+ </refsect1>
+
+ <refsect1>
+ <title>Displaying Timestamps</title>
+
+ <para>Timestamps refer to specific, unique points in time. On
+ display, systemd will format these in the local timezone as
+ follows:</para>
+
+ <programlisting>Fri 2012-11-23 23:02:15 CET</programlisting>
+
+ <para>The weekday is printed in the abbreviated English language form. The formatting is locale-independent.</para>
+
+ <para>In some cases timestamps are shown in the UTC timezone instead of the local timezone, which is indicated via
+ the <literal>UTC</literal> timezone specifier in the output.</para>
+
+ <para>In some cases timestamps are shown with microsecond granularity. In this case the sub-second remainder is
+ separated by a full stop from the seconds component.</para>
+ </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>A timestamp is considered invalid if a weekday is specified and the date does not match the specified day of
+ the week.</para>
+
+ <para>When parsing, systemd will also accept a few special
+ placeholders instead of timestamps: <literal>now</literal> may be
+ used to refer to the current time (or of the invocation of the
+ command that is currently executed). <literal>today</literal>,
+ <literal>yesterday</literal>, and <literal>tomorrow</literal> refer to
+ 00:00:00 of the current day, the day before, or the next day,
+ respectively.</para>
+
+ <para>When parsing, systemd will also accept relative time
+ specifications. A time span (see above) that is prefixed with
+ <literal>+</literal> is evaluated to the current time plus the
+ specified time span. Correspondingly, a time span that is prefixed
+ with <literal>-</literal> is evaluated to the current time minus
+ the specified time span. Instead of prefixing the time span with
+ <literal>+</literal> or <literal>-</literal>, it may also be
+ suffixed with a space and the word <literal>left</literal> or
+ <literal>ago</literal>.</para>
+
+ <para>Finally, a timespan prefixed with <literal>@</literal> is
+ evaluated relative to the UNIX time epoch 1st Jan, 1970,
+ 00:00.</para>
+
+ <para>Examples for valid timestamps and their normalized form
+ (assuming the current time was 2012-11-23 18:15:22 and the timezone
+ was UTC+8, for example TZ=Asia/Shanghai):</para>
+
+ <programlisting> Fri 2012-11-23 11:12:13 → Fri 2012-11-23 11:12:13
+ 2012-11-23 11:12:13 → Fri 2012-11-23 11:12:13
+ 2012-11-23 11:12:13 UTC → Fri 2012-11-23 19:12:13
+ 2012-11-23 → Fri 2012-11-23 00:00:00
+ 12-11-23 → Fri 2012-11-23 00:00:00
+ 11:12:13 → Fri 2012-11-23 11:12:13
+ 11:12 → Fri 2012-11-23 11:12:00
+ now → Fri 2012-11-23 18:15:22
+ today → Fri 2012-11-23 00:00:00
+ today UTC → Fri 2012-11-23 16:00:00
+ yesterday → Fri 2012-11-22 00:00:00
+ tomorrow → Fri 2012-11-24 00:00:00
+tomorrow Pacific/Auckland → Thu 2012-11-23 19:00:00
+ +3h30min → Fri 2012-11-23 21:45:22
+ -5s → Fri 2012-11-23 18:15:17
+ 11min ago → Fri 2012-11-23 18:04:22
+ @1395716396 → Tue 2014-03-25 03:59:56</programlisting>
+
+ <para>Note that timestamps displayed by remote systems with a non-matching timezone are usually not parsable
+ locally, as the timezone component is not understood (unless it happens to be <literal>UTC</literal>).</para>
+
+ <para>Timestamps may also be specified with microsecond granularity. The sub-second remainder is expected separated
+ by a full stop from the seconds component. Example:</para>
+
+ <programlisting>2014-03-25 03:59:56.654563</programlisting>
+
+ <para>In some cases, systemd will display a relative timestamp (relative to the current time, or the time of
+ invocation of the command) instead of or in addition to an absolute timestamp as described above. A relative
+ timestamp is formatted as follows:</para>
+
+ <programlisting>2 months 5 days ago</programlisting>
+
+ <para>Note that a relative timestamp is also accepted where a timestamp is expected (see above).</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Calendar Events</title>
+
+ <para>Calendar events may be used to refer to one or more points
+ in time in a single expression. They form a superset of the
+ absolute timestamps explained above:</para>
+
+ <programlisting>Thu,Fri 2012-*-1,5 11:12:13</programlisting>
+
+ <para>The above refers to 11:12:13 of the first or fifth day of
+ any month of the year 2012, but only if that day is a Thursday or
+ Friday.</para>
+
+ <para>The weekday specification is optional. If specified, it
+ should consist of one or more English language weekday names,
+ either in the abbreviated (Wed) or non-abbreviated (Wednesday)
+ form (case does not matter), separated by commas. Specifying two
+ weekdays separated by <literal>..</literal> refers to a range of
+ continuous weekdays. <literal>,</literal> and <literal>..</literal>
+ may be combined freely.</para>
+
+ <para>In the date and time specifications, any component may be
+ specified as <literal>*</literal> in which case any value will
+ match. Alternatively, each component can be specified as a list of
+ values separated by commas. Values may be suffixed with
+ <literal>/</literal> and a repetition value, which indicates that
+ the value itself and the value plus all multiples of the repetition value
+ are matched. Two values separated by <literal>..</literal> may be used
+ to indicate a range of values; ranges may also be followed with
+ <literal>/</literal> and a repetition value.</para>
+
+ <para>A date specification may use <literal>~</literal> to indicate the
+ last day(s) in a month. For example, <literal>*-02~03</literal> means
+ "the third last day in February," and <literal>Mon *-05~07/1</literal>
+ means "the last Monday in May."</para>
+
+ <para>The seconds component may contain decimal fractions both in
+ the value and the repetition. All fractions are rounded to 6
+ decimal places.</para>
+
+ <para>Either time or date specification may be omitted, in which
+ case the current day and 00:00:00 is implied, respectively. If the
+ second component is not specified, <literal>:00</literal> is
+ assumed.</para>
+
+ <para>Timezone can be specified as the literal string <literal>UTC</literal>, or
+ the local timezone, similar to the supported syntax of timestamps (see above), or the timezone
+ in the IANA timezone database format (also see above).</para>
+
+ <para>The following special expressions may be used as shorthands for longer normalized forms:</para>
+
+ <programlisting> minutely → *-*-* *:*:00
+ hourly → *-*-* *:00:00
+ daily → *-*-* 00:00:00
+ monthly → *-*-01 00:00:00
+ weekly → Mon *-*-* 00:00:00
+ yearly → *-01-01 00:00:00
+ quarterly → *-01,04,07,10-01 00:00:00
+semiannually → *-01,07-01 00:00:00
+ </programlisting>
+
+ <para>Examples for valid timestamps and their
+ normalized form:</para>
+
+<programlisting> Sat,Thu,Mon..Wed,Sat..Sun → Mon..Thu,Sat,Sun *-*-* 00:00:00
+ Mon,Sun 12-*-* 2,1:23 → Mon,Sun 2012-*-* 01,02:23:00
+ Wed *-1 → Wed *-*-01 00:00:00
+ Wed..Wed,Wed *-1 → Wed *-*-01 00:00:00
+ Wed, 17:48 → Wed *-*-* 17:48:00
+Wed..Sat,Tue 12-10-15 1:2:3 → Tue..Sat 2012-10-15 01:02:03
+ *-*-7 0:0:0 → *-*-07 00:00:00
+ 10-15 → *-10-15 00:00:00
+ monday *-12-* 17:00 → Mon *-12-* 17:00:00
+ Mon,Fri *-*-3,1,2 *:30:45 → Mon,Fri *-*-01,02,03 *:30:45
+ 12,14,13,12:20,10,30 → *-*-* 12,13,14:10,20,30:00
+ 12..14:10,20,30 → *-*-* 12..14:10,20,30:00
+ mon,fri *-1/2-1,3 *:30:45 → Mon,Fri *-01/2-01,03 *:30:45
+ 03-05 08:05:40 → *-03-05 08:05:40
+ 08:05:40 → *-*-* 08:05:40
+ 05:40 → *-*-* 05:40:00
+ Sat,Sun 12-05 08:05:40 → Sat,Sun *-12-05 08:05:40
+ Sat,Sun 08:05:40 → Sat,Sun *-*-* 08:05:40
+ 2003-03-05 05:40 → 2003-03-05 05:40:00
+ 05:40:23.4200004/3.1700005 → *-*-* 05:40:23.420000/3.170001
+ 2003-02..04-05 → 2003-02..04-05 00:00:00
+ 2003-03-05 05:40 UTC → 2003-03-05 05:40:00 UTC
+ 2003-03-05 → 2003-03-05 00:00:00
+ 03-05 → *-03-05 00:00:00
+ hourly → *-*-* *:00:00
+ daily → *-*-* 00:00:00
+ daily UTC → *-*-* 00:00:00 UTC
+ monthly → *-*-01 00:00:00
+ weekly → Mon *-*-* 00:00:00
+ weekly Pacific/Auckland → Mon *-*-* 00:00:00 Pacific/Auckland
+ yearly → *-01-01 00:00:00
+ annually → *-01-01 00:00:00
+ *:2/3 → *-*-* *:02/3:00</programlisting>
+
+ <para>Calendar events are used by timer units, see
+ <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details.</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>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>