Cron Expression: 0 0 0/1 1/1 * * - Understanding the Meaning
Cron expressions are used to schedule tasks in various systems, including Linux and Unix-based operating systems. They consist of five or six fields, separated by spaces, that specify the timing and frequency of the task execution. In this article, we will break down the cron expression 0 0 0/1 1/1 * * and explain its meaning.
Fields in a Cron Expression
A cron expression typically consists of five fields, each representing a different aspect of the scheduling:
- Minute (0-59)
- Hour (0-23)
- Day of the month (1-31)
- Month (1-12)
- Day of the week (0-6), where 0 = Sunday
In some cases, a sixth field can be added to specify the username or command to run.
Breaking Down the Expression: 0 0 0/1 1/1 * *
Let's analyze the given cron expression:
0 0 0/1 1/1 * *
Field 1: Minute (0)
The first field specifies the minute of the hour when the task should run. In this case, it is set to 0, which means the task will run at the start of every hour.
Field 2: Hour (0)
The second field specifies the hour of the day when the task should run. Again, it is set to 0, which means the task will run at 12:00 AM (midnight).
Field 3: Day of the month (0/1)
The third field specifies the day of the month when the task should run. The 0/1 syntax indicates that the task will run every 1 day, starting from the 1st day of the month. This means the task will run on the 1st, 2nd, 3rd, ..., 31st day of the month.
Field 4: Month (1/1)
The fourth field specifies the month when the task should run. The 1/1 syntax indicates that the task will run every 1 month, starting from January. This means the task will run in January, February, March, ..., December.
Field 5: Day of the week (*)
The fifth field specifies the day of the week when the task should run. The * is a wildcard character, which means the task will run every day of the week, i.e., Sunday, Monday, Tuesday, ..., Saturday.
In Summary
The cron expression 0 0 0/1 1/1 * * can be read as:
"Run the task at 12:00 AM (midnight), every day, starting from the 1st day of every month, every 1 day, every 1 month, every day of the week."
In other words, the task will run daily at midnight, starting from the first day of every month.
