CRON
Syntax
┌───────────── minute (0 - 59)
│ ┌───────────── hour (0 - 23)
│ │ ┌───────────── day of the month (1 - 31)
│ │ │ ┌───────────── month (1 - 12)
│ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday;
│ │ │ │ │ 7 is also Sunday on some systems)
│ │ │ │ │
│ │ │ │ │
* * * * * <command to execute>
Expression
| Field | Required | Allowed values | Allowed special characters | Remarks |
|---|---|---|---|---|
| Minutes | Yes | 0-59 | * , - | |
| Hours | Yes | 0-23 | * , - | |
| Day of month | Yes | 1-31 | * , - ? L W ? | L W only in some implementations |
| Month | Yes | 1-12 or JAN-DEC | * , - | |
| Day of week | Yes | 0-6 or SUN-SAT | * , - ? L # | ? L # ? L # only in some implementations |
| Year | No | 1970-2099 | * , - | This field is not supported in standard/default implementations. |
-
Comma ( , )
Commas are used to separate items of a list. For example, using “MON,WED,FRI” in the 5th field (day of week) means Mondays, Wednesdays and Fridays
-
Dash( - )
Dash defines ranges. For example, 2000-2010 indicates every year between 2000 and 2010, inclusive
-
Percent ( % )
Percent-signs (%) in the command, unless escaped with backslash (), are changed into newline characters, and all data after the first % are sent to the command as standard input.
-
Question mark (?)
In some implementations, used instead of ‘*’ for leaving either day-of-month or day-of-week blank. Other cron implementations substitute “?” with the start-up time of the cron daemon.
-
Slash (/)
For example, */5 in the minutes field indicates every 5 minutes (see note below about frequencies). It is shorthand for the more verbose POSIX form 5,10,15,20,25,30,35,40,45,50,55,00.
Examples
- every minute
* * * * *
- every 5 minutes
*/5 * * * *
- every 2 hours
* */2 * * *
- 2am daily
0 2 * * *
- every Sunday at 5 PM
0 17 * * sun