Cron Expression: 0 0 21 * * Meaning
Cron expressions are used to schedule tasks to run at specific times or intervals. In this article, we will break down the meaning of the cron expression 0 0 21 * *.
Cron Expression Structure
A cron expression consists of five or six fields, separated by spaces. The five fields are:
- Minute (0-59)
- Hour (0-23)
- Day of the month (1-31)
- Month (1-12)
- Day of the week (0-6), where 0 = Sunday
The sixth field, which is optional, is the year (1970-2099).
**Breaking Down the Expression: 0 0 21 * * **
Let's break down the cron expression 0 0 21 * *:
- Minute:
0- The task will run at minute 0, which means the task will start at the beginning of the hour. - Hour:
0- The task will run at hour 21, which is equivalent to 9:00 PM. - Day of the month:
*- The asterisk is a wildcard character that means "any" value. Therefore, the task will run every day of the month. - Month:
*- Again, the asterisk is a wildcard character, meaning the task will run every month. - Day of the week:
*- The final asterisk indicates that the task will run every day of the week.
Meaning of the Cron Expression
In summary, the cron expression 0 0 21 * * means:
"The task will run every day at 9:00 PM (21:00) sharp."
This expression is useful for scheduling tasks that need to run daily at a specific time, such as daily backups or report generation.
I hope this helps! Let me know if you have any questions.
