Cron expressions-Elastic Compute Service(ECS)-阿里云帮助中心

When you run a Cloud Assistant command in the Elastic Compute Service (ECS) console or by calling an API operation, you can specify a cron expression to define a schedule on which to run the command. This topic describes the basic syntax of cron expressions and provides examples on how to use cron expressions.

Basic syntax of cron expressions

A cron expression is a string that represents the schedule for the execution of a job. A cron expression consists of six or seven fields (time units).

Cron expressions are in the following format:

Seconds Minutes Hours Day-of-month Month Day-of-week [Year]

<Year>: This field is optional.
For a single field:
- Each field can contain specific values, ranges, increments, or special characters.
- If a field has multiple values, separate them with a comma (,).
- Each field supports up to one leading zero. For example, 01 and 02 are allowed in the fields, but 001 and 002 are not.

For information about the value ranges and special characters supported by fields in cron expressions, see the Valid values of fields and Examples sections in this topic.

Valid values of fields

The following table describes the valid value ranges and special characters supported by the fields in cron expressions.

Field	Required	Value range	Special characters
Seconds	Yes	[0, 59]	* , - /
Minutes	Yes	[0, 59]	* , - /
Hours	Yes	[0, 23]	* , - /
Date	Yes	[1, 31]	* , - / ? L W
Month	Yes	[1, 12] or [JAN, DEC]	* , - /
Day-of-week	Yes	[1, 7] or [MON, SUN]. In Cloud Assistant commands, if you use the [1, 7] format, `1` represents Monday and `7` represents Sunday. Important The usage and meanings of cron expressions may vary based on the system, framework, or tool. In scenarios other than Cloud Assistant commands, the meanings of 1 and 7 in [1, 7] may vary. 1 may indicate Sunday and 7 may indicate Saturday.	* , - / ? L #
Year	No	[Current year, 2099]	* , - /

Special characters

Each field in cron expressions supports special characters that have specific meanings.

Special character	Meaning	Example
`*`	Includes all values.	In the `Month` field, `*` means every month.
`,`	A list of enumeration values.	In the `Minutes` field, `5,20` triggers once at the 5th minute and once at the 20th minute.
`-`	Specifies ranges.	In the `Minutes` field, `5-20` triggers every minute from the 5th to the 20th minute.
`/`	Specifies increments.	In the `Minutes` field, `0/15` starts at minute 0 and repeats every 15 minutes. `3/20` starts at minute 3 and repeats every 20 minutes.
`?`	This indicates an unspecified value and is used only for dates and weeks.	If you specify a value in either the `Day-of-month` or `Day-of-week` field, set the other field to `?` to avoid conflicts.
`L`	Stands for "last". It represents the last day and is supported only in the `Day-of-month` and `Day-of-week` fields. Important Do not combine `L` with lists or ranges. This combination can cause logical errors.	In the `Day-of-month` field, `L` means the last day of the month. In the `Day-of-week` field, `L` means the last day of the week—Sunday (`SUN`). If you add a value before `L`, such as `6L` in the `Day-of-week` field, it means the last Saturday of the month.
`W`	Represents the nearest weekday (Monday to Friday) to a specified day. The `W` character does not cross month boundaries. The `LW` combination represents the last weekday of the month.	In the `Day-of-month` field, `5W` triggers on the nearest weekday to the 5th. If the 5th is a Saturday, it triggers on Friday the 4th. If the 5th is a Sunday, it triggers on Monday the 6th. If the 5th falls on a weekday, it triggers on the 5th.
`#`	Specifies a day of the week in the month. Important This character is supported only in the `Day-of-week` field.	In the `Day-of-week` field, `4#2` means the second Thursday of the month.

Examples

Scenario		Value
Run a task at a specific time every day.	Run the task at 10:15 every day.	`0 15 10 ? * *`
Run a task at a specific time every day.	Run the task at 12:00 every day.	`0 0 12 * * ?`
Run a task at specific times every day.	Run the task at 10:00, 14:00, and 16:00 every day.	`0 0 10,14,16 * * ?`
Run a task at a fixed interval.	Run the task every half hour from 09:00 to 17:00 every day.	`0 0/30 9-17 * * ?`
	Run the task every minute from 14:00 to 14:59 every day.	`0 * 14 * * ?`
	Run the task every minute from 14:00 to 14:05 every day.	`0 0-5 14 * * ?`
	Run the task every 5 minutes from 14:00 to 14:55 every day.	`0 0/5 14 * * ?`
	Run the task every 5 minutes from 14:00 to 14:55 and from 18:00 to 18:55 every day.	`0 0/5 14,18 * * ?`
Run a task on specific days of the month or week.	Run the task at 12:00 every Wednesday.	`0 0 12 ? * WED`
	Run the task at 10:15 on the 15th day of every month.	`0 15 10 15 * ?`
	Run the task at 10:15 on the last day of every month.	`0 15 10 L * ?`
	Run the task at 10:15 on the last Saturday of every month.	`0 15 10 ? * 6L`
	Run the task at 10:15 on the 3rd Saturday of every month.	`0 15 10 ? * 6#3`
Run a task on specific days in specific years.	Run the task at 14:10 and 14:44 every Wednesday in March every year.	`0 10,44 14 ? 3 WED`
	Run the task at 10:15 every day in 2022.	`0 15 10 ? * * 2022`
	Run the task at 10:15 every day every year.	`0 15 10 ? * * *`
	Run the task every 5 minutes from 14:00 to 14:55 and from 18:00 to 18:55 every day in 2022.	`0 0/5 14,18 * * ? 2022`
	Run the task at 10:15 on the 3rd Saturday of every month in 2022 and 2023.	`0 15 10 ? * 6#3 2022,2023`
	Run the task every half hour from 9:00 to 17:30 every day in 2022 to 2025.	`0 0/30 9-17 * * ? 2022-2025`
	Run the task at 14:10 and 14:44 every Wednesday in March every 2 years starting from 2022.	`0 10,44 14 ? 3 WED 2022/2`