(from github.com/ramaghattu)
This is just an information which can be added later to the documentation for scheduling crawl jobs and respective Unix formats it follows. Internally, the library used for scheduling jobs is cron4j. Hence the following format should be used below:
A UNIX crontab-like pattern is a string split in five space separated parts. Each part is intented as:
Minutes sub-pattern. During which minutes of the hour should the task been launched? The values range is from 0 to 59.
Hours sub-pattern. During which hours of the day should the task been launched? The values range is from 0 to 23.
Days of month sub-pattern. During which days of the month should the task been launched? The values range is from 1 to 31. The special value L can be used to recognize the last day of month.
Months sub-pattern. During which months of the year should the task been launched? The values range is from 1 (January) to 12 (December), otherwise this sub-pattern allows the aliases “jan”, “feb”, “mar”, “apr”, “may”, “jun”, “jul”, “aug”, “sep”, “oct”, “nov” and “dec”.
Days of week sub-pattern. During which days of the week should the task been launched? The values range is from 0 (Sunday) to 6 (Saturday), otherwise this sub-pattern allows the aliases “sun”, “mon”, “tue”, “wed”, “thu”, “fri” and “sat”.
The star wildcard character is also admitted, indicating “every minute of the hour”, “every hour of the day”, “every day of the month”, “every month of the year” and “every day of the week”, according to the sub-pattern in which it is used.
Once the scheduler is started, a task will be launched when the five parts in its scheduling pattern will be true at the same time.
Some examples:
5 * * * *
This pattern causes a task to be launched once every hour, at the begin of the fifth minute (00:05, 01:05, 02:05 etc.).
This pattern causes a task to be launched every minute.
- 12 * * Mon
This pattern causes a task to be launched every minute during the 12th hour of Monday. - 12 16 * Mon
This pattern causes a task to be launched every minute during the 12th hour of Monday, 16th, but only if the day is the 16th of the month.
Every sub-pattern can contain two or more comma separated values.
59 11 * * 1,2,3,4,5
This pattern causes a task to be launched at 11:59AM on Monday, Tuesday, Wednesday, Thursday and Friday.
Values intervals are admitted and defined using the minus character.
59 11 * * 1-5
This pattern is equivalent to the previous one.
The slash character can be used to identify step values within a range. It can be used both in the form */c and a-b/c. The subpattern is matched every c values of the range 0,maxvalue or a-b.
*/5 * * * *
This pattern causes a task to be launched every 5 minutes (0:00, 0:05, 0:10, 0:15 and so on).
3-18/5 * * * *
This pattern causes a task to be launched every 5 minutes starting from the third minute of the hour, up to the 18th (0:03, 0:08, 0:13, 0:18, 1:03, 1:08 and so on).
*/15 9-17 * * *
This pattern causes a task to be launched every 15 minutes between the 9th and 17th hour of the day (9:00, 9:15, 9:30, 9:45 and so on… note that the last execution will be at 17:45).
All the fresh described syntax rules can be used together. - 12 10-16/2 * *
This pattern causes a task to be launched every minute during the 12th hour of the day, but only if the day is the 10th, the 12th, the 14th or the 16th of the month. - 12 1-15,17,20-25 * *
This pattern causes a task to be launched every minute during the 12th hour of the day, but the day of the month must be between the 1st and the 15th, the 20th and the 25, or at least it must be the 17th.
Finally cron4j lets you combine more scheduling patterns into one, with the pipe character:
0 5 * * *|8 10 * * *|22 17 * * *
This pattern causes a task to be launched every day at 05:00, 10:08 and 17:22.