欄位有哪些

每行包含5個欄位，用製表符或空格隔開，從左至右依次是：

分 時 天 月 星期

每個欄位的取值範圍

分鐘 一小時中(0–59)
時 一天中 (0–23)
天 一個月中(1–31)
月 一年中 (1–12)
星期 一週中 （0 和 7 都代表星期日）

為了每個欄位可以取多個值，可以用下面操作符，按優先順序：

• * 匹配範圍內所有值
• M-N specifies a range of values
• M-N/X or /X steps by intervals of X through the specified range or whole valid range
• A,B,...,Z enumerates multiple values
To allow periodically scheduled tasks to produce even load on the system, the symbol H (for “hash”) should be used wherever possible. For example, using 0 0

* * for a dozen daily jobs will cause a large spike at midnight. In contrast, using H H * * * would still execute each job once a day, but not all at the same time, better using limited resources.
The H symbol can be used with a range. For example, H H(0-7) * * * means some time between 12:00 AM (midnight) to 7:59 AM. You can also use step intervals with H, with or without ranges.
The H symbol can be thought of as a random value over a range, but it actually is a hash of the job name, not a random function, so that the value remains stable for any given project.
Beware that for the day of month field, short cycles such as /3 or H/3 will not work consistently near the end of most months, due to variable month lengths. For example, /3 will run on the 1st, 4th, …31st days of a long month, then again the next day of the next month. Hashes are always chosen in the 1-28 range, so H/3 will produce a gap between runs of between 3 and 6 days at the end of a month. (Longer cycles will also have inconsistent lengths but the effect may be relatively less noticeable.)
Empty lines and lines that start with # will be ignored as comments.
In addition, @yearly, @annually, @monthly, @weekly, @daily, @midnight, and @hourly are supported as convenient aliases. These use the hash system for automatic balancing. For example, @hourly is the same as H * * * * and could mean at any time during the hour. @midnight actually means some time between 12:00 AM and 2:59 AM.
Examples:

every fifteen minutes (perhaps at :07, :22, :37, :52)

H/15 * * * *

every ten minutes in the first half of every hour (three times, perhaps at :04, :14, :24)

H(0-29)/10 * * * *

once every two hours at 45 minutes past the hour starting at 9:45 AM and finishing at 3:45 PM every weekday.

45 9-16/2 * * 1-5

once in every two hours slot between 9 AM and 5 PM every weekday (perhaps at 10:38 AM, 12:38 PM, 2:38 PM, 4:38 PM)

H H(9-16)/2 * * 1-5

once a day on the 1st and 15th of every month except December

H H 1,15 1-11 *