man/systemd.time.xml

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   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
  69 2hours
  70 48hr
  71 1y 12month
  72 55s500ms
  73 300ms20s 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   </refsect1>
  79
  80   <refsect1>
  81     <title>Displaying Timestamps</title>
  82
  83     <para>Timestamps refer to specific, unique points in time. On
  84     display, systemd will format these in the local timezone as
  85     follows:</para>
  86
  87     <programlisting>Fri 2012-11-23 23:02:15 CET</programlisting>
  88
  89     <para>The weekday is printed in the abbreviated English language form. The formatting is locale-independent.</para>
  90
  91     <para>In some cases timestamps are shown in the UTC timezone instead of the local timezone, which is indicated via
  92     the <literal>UTC</literal> timezone specifier in the output.</para>
  93
  94     <para>In some cases timestamps are shown with microsecond granularity. In this case the sub-second remainder is
  95     separated by a full stop from the seconds component.</para>
  96   </refsect1>
  97
  98   <refsect1>
  99     <title>Parsing Timestamps</title>
 100
 101     <para>When parsing, systemd will accept a similar syntax, but expects no timezone specification, unless it is given
 102     as the literal string <literal>UTC</literal> (for the UTC timezone), or is specified to be the locally configured
 103     timezone, or the timezone name in the IANA timezone database format. The complete list of timezones
 104     supported on your system can be obtained using the <literal>timedatectl list-timezones</literal>
 105     (see <citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>).
 106     Using IANA format is recommended over local timezone names, as less prone to errors (eg: with local timezone it's possible to
 107     specify daylight saving time in winter, while it's incorrect). The weekday specification is optional, but when
 108     the weekday is specified, it must either be in the abbreviated (<literal>Wed</literal>) or non-abbreviated
 109     (<literal>Wednesday</literal>) English language form (case does not matter), and is not subject to the locale
 110     choice of the user.  Either the date, or the time part may be omitted, in which case the current date or 00:00:00,
 111     respectively, is assumed. The seconds component of the time may also be omitted, in which case ":00" is
 112     assumed. Year numbers may be specified in full or may be abbreviated (omitting the century).</para>
 113
 114     <para>A timestamp is considered invalid if a weekday is specified and the date does not match the specified day of
 115     the week.</para>
 116
 117     <para>When parsing, systemd will also accept a few special
 118     placeholders instead of timestamps: <literal>now</literal> may be
 119     used to refer to the current time (or of the invocation of the
 120     command that is currently executed). <literal>today</literal>,
 121     <literal>yesterday</literal>, and <literal>tomorrow</literal> refer to
 122     00:00:00 of the current day, the day before, or the next day,
 123     respectively.</para>
 124
 125     <para>When parsing, systemd will also accept relative time
 126     specifications. A time span (see above) that is prefixed with
 127     <literal>+</literal> is evaluated to the current time plus the
 128     specified time span. Correspondingly, a time span that is prefixed
 129     with <literal>-</literal> is evaluated to the current time minus
 130     the specified time span. Instead of prefixing the time span with
 131     <literal>+</literal> or <literal>-</literal>, it may also be
 132     suffixed with a space and the word <literal>left</literal> or
 133     <literal>ago</literal>.</para>
 134
 135     <para>Finally, a timespan prefixed with <literal>@</literal> is
 136     evaluated relative to the UNIX time epoch 1st Jan, 1970,
 137     00:00.</para>
 138
 139     <para>Examples for valid timestamps and their normalized form
 140     (assuming the current time was 2012-11-23 18:15:22 and the timezone
 141     was UTC+8, for example TZ=Asia/Shanghai):</para>
 142
 143     <programlisting>  Fri 2012-11-23 11:12:13 → Fri 2012-11-23 11:12:13
 144       2012-11-23 11:12:13 → Fri 2012-11-23 11:12:13
 145   2012-11-23 11:12:13 UTC → Fri 2012-11-23 19:12:13
 146                2012-11-23 → Fri 2012-11-23 00:00:00
 147                  12-11-23 → Fri 2012-11-23 00:00:00
 148                  11:12:13 → Fri 2012-11-23 11:12:13
 149                     11:12 → Fri 2012-11-23 11:12:00
 150                       now → Fri 2012-11-23 18:15:22
 151                     today → Fri 2012-11-23 00:00:00
 152                 today UTC → Fri 2012-11-23 16:00:00
 153                 yesterday → Fri 2012-11-22 00:00:00
 154                  tomorrow → Fri 2012-11-24 00:00:00
 155 tomorrow Pacific/Auckland → Thu 2012-11-23 19:00:00
 156                  +3h30min → Fri 2012-11-23 21:45:22
 157                       -5s → Fri 2012-11-23 18:15:17
 158                 11min ago → Fri 2012-11-23 18:04:22
 159               @1395716396 → Tue 2014-03-25 03:59:56</programlisting>
 160
 161     <para>Note that timestamps displayed by remote systems with a non-matching timezone are usually not parsable
 162     locally, as the timezone component is not understood (unless it happens to be <literal>UTC</literal>).</para>
 163
 164     <para>Timestamps may also be specified with microsecond granularity. The sub-second remainder is expected separated
 165     by a full stop from the seconds component. Example:</para>
 166
 167     <programlisting>2014-03-25 03:59:56.654563</programlisting>
 168
 169     <para>In some cases, systemd will display a relative timestamp (relative to the current time, or the time of
 170     invocation of the command) instead of or in addition to an absolute timestamp as described above. A relative
 171     timestamp is formatted as follows:</para>
 172
 173     <programlisting>2 months 5 days ago</programlisting>
 174
 175     <para>Note that a relative timestamp is also accepted where a timestamp is expected (see above).</para>
 176   </refsect1>
 177
 178   <refsect1>
 179     <title>Calendar Events</title>
 180
 181     <para>Calendar events may be used to refer to one or more points
 182     in time in a single expression. They form a superset of the
 183     absolute timestamps explained above:</para>
 184
 185     <programlisting>Thu,Fri 2012-*-1,5 11:12:13</programlisting>
 186
 187     <para>The above refers to 11:12:13 of the first or fifth day of
 188     any month of the year 2012, but only if that day is a Thursday or
 189     Friday.</para>
 190
 191     <para>The weekday specification is optional. If specified, it
 192     should consist of one or more English language weekday names,
 193     either in the abbreviated (Wed) or non-abbreviated (Wednesday)
 194     form (case does not matter), separated by commas. Specifying two
 195     weekdays separated by <literal>..</literal> refers to a range of
 196     continuous weekdays. <literal>,</literal> and <literal>..</literal>
 197     may be combined freely.</para>
 198
 199     <para>In the date and time specifications, any component may be
 200     specified as <literal>*</literal> in which case any value will
 201     match. Alternatively, each component can be specified as a list of
 202     values separated by commas. Values may be suffixed with
 203     <literal>/</literal> and a repetition value, which indicates that
 204     the value itself and the value plus all multiples of the repetition value
 205     are matched.  Two values separated by <literal>..</literal> may be used
 206     to indicate a range of values; ranges may also be followed with
 207     <literal>/</literal> and a repetition value.</para>
 208
 209     <para>A date specification may use <literal>~</literal> to indicate the
 210     last day(s) in a month. For example, <literal>*-02~03</literal> means
 211     "the third last day in February," and <literal>Mon *-05~07/1</literal>
 212     means "the last Monday in May."</para>
 213
 214     <para>The seconds component may contain decimal fractions both in
 215     the value and the repetition. All fractions are rounded to 6
 216     decimal places.</para>
 217
 218     <para>Either time or date specification may be omitted, in which
 219     case the current day and 00:00:00 is implied, respectively. If the
 220     second component is not specified, <literal>:00</literal> is
 221     assumed.</para>
 222
 223     <para>Timezone can be specified as the literal string <literal>UTC</literal>, or
 224     the local timezone, similar to the supported syntax of timestamps (see above), or the timezone
 225     in the IANA timezone database format (also see above).</para>
 226
 227   <para>The following special expressions may be used as shorthands for longer normalized forms:</para>
 228
 229     <programlisting>    minutely → *-*-* *:*:00
 230       hourly → *-*-* *:00:00
 231        daily → *-*-* 00:00:00
 232      monthly → *-*-01 00:00:00
 233       weekly → Mon *-*-* 00:00:00
 234       yearly → *-01-01 00:00:00
 235    quarterly → *-01,04,07,10-01 00:00:00
 236 semiannually → *-01,07-01 00:00:00
 237    </programlisting>
 238
 239     <para>Examples for valid timestamps and their
 240     normalized form:</para>
 241
 242 <programlisting>  Sat,Thu,Mon..Wed,Sat..Sun → Mon..Thu,Sat,Sun *-*-* 00:00:00
 243       Mon,Sun 12-*-* 2,1:23 → Mon,Sun 2012-*-* 01,02:23:00
 244                     Wed *-1 → Wed *-*-01 00:00:00
 245            Wed..Wed,Wed *-1 → Wed *-*-01 00:00:00
 246                  Wed, 17:48 → Wed *-*-* 17:48:00
 247 Wed..Sat,Tue 12-10-15 1:2:3 → Tue..Sat 2012-10-15 01:02:03
 248                 *-*-7 0:0:0 → *-*-07 00:00:00
 249                       10-15 → *-10-15 00:00:00
 250         monday *-12-* 17:00 → Mon *-12-* 17:00:00
 251   Mon,Fri *-*-3,1,2 *:30:45 → Mon,Fri *-*-01,02,03 *:30:45
 252        12,14,13,12:20,10,30 → *-*-* 12,13,14:10,20,30:00
 253             12..14:10,20,30 → *-*-* 12..14:10,20,30:00
 254   mon,fri *-1/2-1,3 *:30:45 → Mon,Fri *-01/2-01,03 *:30:45
 255              03-05 08:05:40 → *-03-05 08:05:40
 256                    08:05:40 → *-*-* 08:05:40
 257                       05:40 → *-*-* 05:40:00
 258      Sat,Sun 12-05 08:05:40 → Sat,Sun *-12-05 08:05:40
 259            Sat,Sun 08:05:40 → Sat,Sun *-*-* 08:05:40
 260            2003-03-05 05:40 → 2003-03-05 05:40:00
 261  05:40:23.4200004/3.1700005 → *-*-* 05:40:23.420000/3.170001
 262              2003-02..04-05 → 2003-02..04-05 00:00:00
 263        2003-03-05 05:40 UTC → 2003-03-05 05:40:00 UTC
 264                  2003-03-05 → 2003-03-05 00:00:00
 265                       03-05 → *-03-05 00:00:00
 266                      hourly → *-*-* *:00:00
 267                       daily → *-*-* 00:00:00
 268                   daily UTC → *-*-* 00:00:00 UTC
 269                     monthly → *-*-01 00:00:00
 270                      weekly → Mon *-*-* 00:00:00
 271     weekly Pacific/Auckland → Mon *-*-* 00:00:00 Pacific/Auckland
 272                      yearly → *-01-01 00:00:00
 273                    annually → *-01-01 00:00:00
 274                       *:2/3 → *-*-* *:02/3:00</programlisting>
 275
 276       <para>Calendar events are used by timer units, see
 277       <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 278       for details.</para>
 279
 280       <para>Use the <command>calendar</command> command of
 281       <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry> to validate
 282       and normalize calendar time specifications for testing purposes. The tool also calculates when a specified
 283       calendar event would elapse next.</para>
 284   </refsect1>
 285
 286   <refsect1>
 287       <title>See Also</title>
 288       <para>
 289         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 290         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 291         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 292         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 293         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 294         <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 295       </para>
 296   </refsect1>
 297
 298 </refentry>