What is the format of the linux task schedule string?

The Linux task schedule string is "crontab", and the format is "* * * * * command": 1. The first * represents the hour; 2. The second * represents the day of the week; 3. The third * represents the day of the month; 4. The fourth * represents the month; 5. command represents the command/script.

The operating system of this tutorial: Linux5.18.14 system, Dell G3 computer.

In Linux, the task plan uses the crontab (cron table) string to specify the execution time of the task. The crontab string consists of 5 or 6 fields, each field is separated by spaces or tabs, indicating the execution time and frequency of the task.

The standard cron expression format is as follows:

* * * * * command
│ │ │ │ │
│ │ │ │ └─── 命令/脚本
│ │ │ └───── 第几个月份 (1 - 12)
│ │ └─────── 每月的第几天 (1 - 31)
│ └───────── 每周的第几天 (0 - 7,其中 0 和 7 都代表星期日)
└─────────── 小时 (0 - 23)

The five fields above represent minutes, hours, days of the month, months, and days of the week respectively. The wildcard "*" means match all possible values. For example, use " * " to mean every minute, and " */5 " to mean every 5 minutes.

In addition, you can also use special characters to represent a more flexible plan:

• The ellipsis (-) represents a range of consecutive values, such as "9-17" Represents hours from 9 to 17.

• Comma (,) is used to list multiple discrete values, such as "1,3,5" for 1, 3, and 5.

• The asterisk (*) means matching all possible values, such as " * " means every minute, every hour or every day.

• Slash (/) is used to specify the interval, such as "*/5" means every 5 units.

Here are some examples:

• Run the script every day at 2 PM: 0 14 * * * command

• Run the script every Sunday at 3 am: 0 3 * * 0 command

• Run the script every hour: 0 * * * * command

• Run the script every 5 minutes: */5 * * * * command

It should be noted that users can use the crontab -e command to edit their own cron expressions and Save it to the task schedule. Use the crontab -l command to list all cron tasks of the current user.

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