Cron spec

CRON Expression Format

A cron expression represents a set of times, using 6 space-separated fields.

Field name   | Mandatory? | Allowed values  | Allowed special characters
----------   | ---------- | --------------  | --------------------------
Seconds      | Yes        | 0-59            | * / , -
Minutes      | Yes        | 0-59            | * / , -
Hours        | Yes        | 0-23            | * / , -
Day of month | Yes        | 1-31            | * / , - ?
Month        | Yes        | 1-12 or JAN-DEC | * / , -
Day of week  | Yes        | 0-6 or SUN-SAT  | * / , - ?

Note: Month and Day-of-week field values are case insensitive. “SUN”, “Sun”, and “sun” are equally accepted.

Special Characters

Asterisk ( * )

The asterisk indicates that the cron expression will match for all values of the field; e.g., using an asterisk in the 5th field (month) would indicate every month.

Slash ( / )

Slashes are used to describe increments of ranges. For example 3-5915 in the 1st field (minutes) would indicate the 3rd minute of the hour and every 15 minutes thereafter. The form “*\/…” is equivalent to the form “first-last/…”, that is, an increment over the largest possible range of the field. The form “N/…” is accepted as meaning “N-MAX/…”, that is, starting at N, use the increment until the end of that specific range. It does not wrap around.

Comma ( , )

Commas are used to separate items of a list. For example, using “MON,WED,FRI” in the 5th field (day of week) would mean Mondays, Wednesdays and Fridays.

Hyphen ( - )

Hyphens are used to define ranges. For example, 9-17 would indicate every hour between 9am and 5pm inclusive.

Question mark ( ? )

Question mark may be used instead of ‘*’ for leaving either day-of-month or day-of-week blank.

Predefined schedules

You may use one of several pre-defined schedules in place of a cron expression.

Entry                  | Description                                | Equivalent To
-----                  | -----------                                | -------------
@yearly (or @annually) | Run once a year, midnight, Jan. 1st        | 0 0 0 1 1 *
@monthly               | Run once a month, midnight, first of month | 0 0 0 1 * *
@weekly                | Run once a week, midnight on Sunday        | 0 0 0 * * 0
@daily (or @midnight)  | Run once a day, midnight                   | 0 0 0 * * *
@hourly                | Run once an hour, beginning of hour        | 0 0 * * * *
@minutely              | Run once a minute, beginning of minute     | 0 * * * * *

Intervals

You may also schedule a job to execute at fixed intervals. This is supported by formatting the cron spec like this:

@every <duration>

where “duration” is a string accepted by time.ParseDuration (http://golang.org/pkg/time/#ParseDuration).

For example, “@every 1h30m10s” would indicate a schedule that activates every 1 hour, 30 minutes, 10 seconds.

Note: The interval does not take the job runtime into account. For example, if a job takes 3 minutes to run, and it is scheduled to run every 5 minutes, it will have only 2 minutes of idle time between each run.

Fixed times

You may also want to schedule a job to be executed once. This is supported by formatting the cron spec like this:

@at <datetime>

Where “datetime” is a string accepted by time.Parse in RFC3339 format (https://golang.org/pkg/time/#Parse).

For example, “@at 2018-01-02T15:04:00Z” would run the job on the specified date and time assuming UTC timezone.

Time zones

Dkron is able to schedule jobs in time zones, if you specify the timezone parameter in a job definition.

If the time zone is not specified, the following rules apply:

All interpretation and scheduling is done in the machine’s local time zone (as provided by the Go time package (http://www.golang.org/pkg/time).

Be aware that jobs scheduled during daylight-savings leap-ahead transitions will not be run!

If you specify timezone the job will be schduled taking into account daylight-savings and leap-ahead transitions, running the job in the actual time in the specified time zone.