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4<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
5
6<refentry id="systemd.time">
7
8  <refentryinfo>
9    <title>systemd.time</title>
10    <productname>systemd</productname>
11  </refentryinfo>
12
13  <refmeta>
14    <refentrytitle>systemd.time</refentrytitle>
15    <manvolnum>7</manvolnum>
16  </refmeta>
17
18  <refnamediv>
19    <refname>systemd.time</refname>
20    <refpurpose>Time and date specifications</refpurpose>
21  </refnamediv>
22
23  <refsect1>
24    <title>Description</title>
25
26    <para>In systemd, timestamps, time spans, and calendar events are
27    displayed and may be specified in closely related syntaxes.</para>
28  </refsect1>
29
30  <refsect1>
31    <title>Displaying Time Spans</title>
32
33    <para>Time spans refer to time durations. On display, systemd will present time spans as a space-separated series
34    of time values each suffixed by a time unit. Example:</para>
35
36    <programlisting>2h 30min</programlisting>
37
38    <para>All specified time values are meant to be added up. The above hence refers to 150 minutes. Display is
39    locale-independent, only English names for the time units are used.</para>
40  </refsect1>
41
42  <refsect1>
43    <title>Parsing Time Spans</title>
44
45    <para>When parsing, systemd will accept the same time span syntax.
46    Separating spaces may be omitted. The following time units are
47    understood:</para>
48
49    <itemizedlist>
50      <listitem><para>usec, us, µs</para></listitem>
51      <listitem><para>msec, ms</para></listitem>
52      <listitem><para>seconds, second, sec, s</para></listitem>
53      <listitem><para>minutes, minute, min, m</para></listitem>
54      <listitem><para>hours, hour, hr, h</para></listitem>
55      <listitem><para>days, day, d</para></listitem>
56      <listitem><para>weeks, week, w</para></listitem>
57      <listitem><para>months, month, M (defined as 30.44 days)</para></listitem>
58      <listitem><para>years, year, y (defined as 365.25 days)</para></listitem>
59    </itemizedlist>
60
61    <para>If no time unit is specified, generally seconds are assumed, but some exceptions exist and are marked as
62    such. In a few cases <literal>ns</literal>, <literal>nsec</literal> is accepted too, where the granularity of the
63    time span permits this. Parsing is generally locale-independent, non-English names for the time units are not
64    accepted.</para>
65
66    <para>Examples for valid time span specifications:</para>
67
68    <programlisting>2 h
692hours
7048hr
711y 12month
7255s500ms
73300ms20s 5day</programlisting>
74
75    <para>One can use the <command>timespan</command> command of
76    <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
77    to normalise a textual time span for testing and validation purposes.</para>
78
79    <para>Internally, systemd generally operates with microsecond time granularity, while the default time
80    unit in user-configurable time spans is usually seconds (see above). This disparity becomes visible when
81    comparing the same settings in the (high-level) unit file syntax with the matching (more low-level) D-Bus
82    properties (which are what
83    <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
84    <command>show</command> command displays). The former typically are suffixed with <literal>…Sec</literal>
85    to indicate the default unit of seconds, the latter are typically suffixed with <literal>…USec</literal>
86    to indicate the underlying low-level time unit, even if they both encapsulate the very same
87    settings.</para>
88  </refsect1>
89
90  <refsect1>
91    <title>Displaying Timestamps</title>
92
93    <para>Timestamps refer to specific, unique points in time. On
94    display, systemd will format these in the local timezone as
95    follows:</para>
96
97    <programlisting>Fri 2012-11-23 23:02:15 CET</programlisting>
98
99    <para>The weekday is printed in the abbreviated English language form. The formatting is locale-independent.</para>
100
101    <para>In some cases timestamps are shown in the UTC timezone instead of the local timezone, which is indicated via
102    the <literal>UTC</literal> timezone specifier in the output.</para>
103
104    <para>In some cases timestamps are shown with microsecond granularity. In this case the sub-second remainder is
105    separated by a full stop from the seconds component.</para>
106  </refsect1>
107
108  <refsect1>
109    <title>Parsing Timestamps</title>
110
111    <para>When parsing, systemd will accept a similar syntax, but expects no timezone specification, unless
112    it is given as the literal string <literal>UTC</literal> (for the UTC timezone), or is specified to be
113    the locally configured timezone, or the timezone name in the IANA timezone database format. The complete
114    list of timezones supported on your system can be obtained using the <literal>timedatectl
115    list-timezones</literal> (see
116    <citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>).  Using
117    IANA format is recommended over local timezone names, as less prone to errors (e.g. with local timezone
118    it's possible to specify daylight saving time in winter, even though that is not correct). The weekday
119    specification is optional, but when the weekday is specified, it must either be in the abbreviated
120    (<literal>Wed</literal>) or non-abbreviated (<literal>Wednesday</literal>) English language form (case
121    does not matter), and is not subject to the locale choice of the user. Either the date, or the time part
122    may be omitted, in which case the current date or 00:00:00, respectively, is assumed. The seconds
123    component of the time may also be omitted, in which case ":00" is assumed. Year numbers may be specified
124    in full or may be abbreviated (omitting the century).</para>
125
126    <para>A timestamp is considered invalid if a weekday is specified and the date does not match the specified day of
127    the week.</para>
128
129    <para>When parsing, systemd will also accept a few special
130    placeholders instead of timestamps: <literal>now</literal> may be
131    used to refer to the current time (or of the invocation of the
132    command that is currently executed). <literal>today</literal>,
133    <literal>yesterday</literal>, and <literal>tomorrow</literal> refer to
134    00:00:00 of the current day, the day before, or the next day,
135    respectively.</para>
136
137    <para>When parsing, systemd will also accept relative time
138    specifications. A time span (see above) that is prefixed with
139    <literal>+</literal> is evaluated to the current time plus the
140    specified time span. Correspondingly, a time span that is prefixed
141    with <literal>-</literal> is evaluated to the current time minus
142    the specified time span. Instead of prefixing the time span with
143    <literal>+</literal> or <literal>-</literal>, it may also be
144    suffixed with a space and the word <literal>left</literal> or
145    <literal>ago</literal>.</para>
146
147    <para>Finally, a timespan prefixed with <literal>@</literal> is
148    evaluated relative to the UNIX time epoch 1st Jan, 1970,
149    00:00.</para>
150
151    <para>Examples for valid timestamps and their normalized form (assuming the current time was 2012-11-23
152    18:15:22 and the timezone was UTC+8, for example <literal>TZ=:Asia/Shanghai</literal>):</para>
153
154    <programlisting>  Fri 2012-11-23 11:12:13 → Fri 2012-11-23 11:12:13
155      2012-11-23 11:12:13 → Fri 2012-11-23 11:12:13
156  2012-11-23 11:12:13 UTC → Fri 2012-11-23 19:12:13
157               2012-11-23 → Fri 2012-11-23 00:00:00
158                 12-11-23 → Fri 2012-11-23 00:00:00
159                 11:12:13 → Fri 2012-11-23 11:12:13
160                    11:12 → Fri 2012-11-23 11:12:00
161                      now → Fri 2012-11-23 18:15:22
162                    today → Fri 2012-11-23 00:00:00
163                today UTC → Fri 2012-11-23 16:00:00
164                yesterday → Fri 2012-11-22 00:00:00
165                 tomorrow → Fri 2012-11-24 00:00:00
166tomorrow Pacific/Auckland → Thu 2012-11-23 19:00:00
167                 +3h30min → Fri 2012-11-23 21:45:22
168                      -5s → Fri 2012-11-23 18:15:17
169                11min ago → Fri 2012-11-23 18:04:22
170              @1395716396 → Tue 2014-03-25 03:59:56</programlisting>
171
172    <para>Note that timestamps displayed by remote systems with a non-matching timezone are usually not parsable
173    locally, as the timezone component is not understood (unless it happens to be <literal>UTC</literal>).</para>
174
175    <para>Timestamps may also be specified with microsecond granularity. The sub-second remainder is expected separated
176    by a full stop from the seconds component. Example:</para>
177
178    <programlisting>2014-03-25 03:59:56.654563</programlisting>
179
180    <para>In some cases, systemd will display a relative timestamp (relative to the current time, or the time of
181    invocation of the command) instead of or in addition to an absolute timestamp as described above. A relative
182    timestamp is formatted as follows:</para>
183
184    <programlisting>2 months 5 days ago</programlisting>
185
186    <para>Note that a relative timestamp is also accepted where a timestamp is expected (see above).</para>
187
188    <para>Use the <command>timestamp</command> command of
189    <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry> to
190    validate and normalize timestamps for testing purposes.</para>
191  </refsect1>
192
193  <refsect1>
194    <title>Calendar Events</title>
195
196    <para>Calendar events may be used to refer to one or more points
197    in time in a single expression. They form a superset of the
198    absolute timestamps explained above:</para>
199
200    <programlisting>Thu,Fri 2012-*-1,5 11:12:13</programlisting>
201
202    <para>The above refers to 11:12:13 of the first or fifth day of
203    any month of the year 2012, but only if that day is a Thursday or
204    Friday.</para>
205
206    <para>The weekday specification is optional. If specified, it
207    should consist of one or more English language weekday names,
208    either in the abbreviated (Wed) or non-abbreviated (Wednesday)
209    form (case does not matter), separated by commas. Specifying two
210    weekdays separated by <literal>..</literal> refers to a range of
211    continuous weekdays. <literal>,</literal> and <literal>..</literal>
212    may be combined freely.</para>
213
214    <para>In the date and time specifications, any component may be specified as <literal>*</literal> in
215    which case any value will match. Alternatively, each component can be specified as a list of values
216    separated by commas. Values may be suffixed with <literal>/</literal> and a repetition value, which
217    indicates that the value itself and the value plus all multiples of the repetition value are matched.
218    Two values separated by <literal>..</literal> may be used to indicate a range of values; ranges may also
219    be followed with <literal>/</literal> and a repetition value, in which case the expression matches all
220    times starting with the start value, and continuing with all multiples of the repetition value relative
221    to the start value, ending at the end value the latest.</para>
222
223    <para>A date specification may use <literal>~</literal> to indicate the
224    last day(s) in a month. For example, <literal>*-02~03</literal> means
225    "the third last day in February," and <literal>Mon *-05~07/1</literal>
226    means "the last Monday in May."</para>
227
228    <para>The seconds component may contain decimal fractions both in
229    the value and the repetition. All fractions are rounded to 6
230    decimal places.</para>
231
232    <para>Either time or date specification may be omitted, in which
233    case the current day and 00:00:00 is implied, respectively. If the
234    second component is not specified, <literal>:00</literal> is
235    assumed.</para>
236
237    <para>Timezone can be specified as the literal string <literal>UTC</literal>, or
238    the local timezone, similar to the supported syntax of timestamps (see above), or the timezone
239    in the IANA timezone database format (also see above).</para>
240
241  <para>The following special expressions may be used as shorthands for longer normalized forms:</para>
242
243    <programlisting>    minutely → *-*-* *:*:00
244      hourly → *-*-* *:00:00
245       daily → *-*-* 00:00:00
246     monthly → *-*-01 00:00:00
247      weekly → Mon *-*-* 00:00:00
248      yearly → *-01-01 00:00:00
249   quarterly → *-01,04,07,10-01 00:00:00
250semiannually → *-01,07-01 00:00:00
251   </programlisting>
252
253    <para>Examples for valid timestamps and their
254    normalized form:</para>
255
256<programlisting>  Sat,Thu,Mon..Wed,Sat..Sun → Mon..Thu,Sat,Sun *-*-* 00:00:00
257      Mon,Sun 12-*-* 2,1:23 → Mon,Sun 2012-*-* 01,02:23:00
258                    Wed *-1 → Wed *-*-01 00:00:00
259           Wed..Wed,Wed *-1 → Wed *-*-01 00:00:00
260                 Wed, 17:48 → Wed *-*-* 17:48:00
261Wed..Sat,Tue 12-10-15 1:2:3 → Tue..Sat 2012-10-15 01:02:03
262                *-*-7 0:0:0 → *-*-07 00:00:00
263                      10-15 → *-10-15 00:00:00
264        monday *-12-* 17:00 → Mon *-12-* 17:00:00
265  Mon,Fri *-*-3,1,2 *:30:45 → Mon,Fri *-*-01,02,03 *:30:45
266       12,14,13,12:20,10,30 → *-*-* 12,13,14:10,20,30:00
267            12..14:10,20,30 → *-*-* 12..14:10,20,30:00
268  mon,fri *-1/2-1,3 *:30:45 → Mon,Fri *-01/2-01,03 *:30:45
269             03-05 08:05:40 → *-03-05 08:05:40
270                   08:05:40 → *-*-* 08:05:40
271                      05:40 → *-*-* 05:40:00
272     Sat,Sun 12-05 08:05:40 → Sat,Sun *-12-05 08:05:40
273           Sat,Sun 08:05:40 → Sat,Sun *-*-* 08:05:40
274           2003-03-05 05:40 → 2003-03-05 05:40:00
275 05:40:23.4200004/3.1700005 → *-*-* 05:40:23.420000/3.170001
276             2003-02..04-05 → 2003-02..04-05 00:00:00
277       2003-03-05 05:40 UTC → 2003-03-05 05:40:00 UTC
278                 2003-03-05 → 2003-03-05 00:00:00
279                      03-05 → *-03-05 00:00:00
280                     hourly → *-*-* *:00:00
281                      daily → *-*-* 00:00:00
282                  daily UTC → *-*-* 00:00:00 UTC
283                    monthly → *-*-01 00:00:00
284                     weekly → Mon *-*-* 00:00:00
285    weekly Pacific/Auckland → Mon *-*-* 00:00:00 Pacific/Auckland
286                     yearly → *-01-01 00:00:00
287                   annually → *-01-01 00:00:00
288                      *:2/3 → *-*-* *:02/3:00</programlisting>
289
290      <para>Calendar events are used by timer units, see
291      <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
292      for details.</para>
293
294      <para>Use the <command>calendar</command> command of
295      <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry> to validate
296      and normalize calendar time specifications for testing purposes. The tool also calculates when a specified
297      calendar event would occur next.</para>
298  </refsect1>
299
300  <refsect1>
301      <title>See Also</title>
302      <para>
303        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
304        <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
305        <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
306        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
307        <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
308        <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
309      </para>
310  </refsect1>
311
312</refentry>
313