Cron Expression: 0 0 3 * * Meaning Explained
In Linux and Unix-like operating systems, cron jobs are used to schedule tasks to run at specific times or intervals. A cron expression is a string consisting of five or six fields separated by spaces, used to specify the timing of a cron job. One common cron expression is 0 0 3 * *, but what does it mean?
Breaking Down the Cron Expression
Let's break down the 0 0 3 * * cron expression into its individual components:
Minute (0)
The first field represents the minute of the hour, ranging from 0 to 59. In this case, the value is 0, which means the task will run at the start of the hour.
Hour (0)
The second field represents the hour of the day, ranging from 0 to 23. In this case, the value is also 0, which means the task will run at midnight.
Day of the Month (3)
The third field represents the day of the month, ranging from 1 to 31. In this case, the value is 3, which means the task will run on the 3rd day of the month.
Month (*)
The fourth field represents the month of the year, ranging from 1 to 12. The asterisk (*) is a wildcard character, which means the task will run every month.
Day of the Week (*)
The fifth field represents the day of the week, ranging from 0 (Sunday) to 6 (Saturday). The asterisk (*) is again a wildcard character, which means the task will run every day of the week.
What Does the Cron Expression Mean?
Putting it all together, the 0 0 3 * * cron expression means:
"Run the task at 3:00 AM on the 3rd day of every month, every day of the week."
In other words, the task will run at 3:00 AM on the 3rd day of January, February, March, and so on, every year.
Conclusion
Cron expressions can be complex and confusing, but by breaking them down into their individual components, it's easier to understand their meaning. In this case, the 0 0 3 * * cron expression schedules a task to run at 3:00 AM on the 3rd day of every month, every day of the week.
