Linux crontab Command Detailed

1.crontab Command Overview

　　

Command parameters:

-u User: Used to set a user's crontab service, for example, "-u ixdba" means to set IXDBA user's crontab service, this parameter is usually run by the root user.

File:file is the name of the command file, which indicates that file is the Crontab task list and loaded into crontab. If this file is not specified on the command line, the crontab command will accept the commands typed on the standard input (keyboard) and load them into crontab.

-E: Edits the contents of a user's crontab file. If you do not specify a user, the crontab file for the current user is edited.

-L: Displays the contents of a user's crontab file, or displays the contents of the current user's crontab file if no user is specified.

-r: Deletes a user's crontab file from the/var/spool/cron directory and, if no user is specified, deletes the current user's crontab file by default.

-I: Give a confirmation prompt when deleting a user's crontab file.

Meaning of the 2.crontab command

In the crontab file created by the user, each line represents a task, each field of each row represents a setting, its format is divided into six fields, the first five is the time setting segment, and the sixth paragraph is the command segment to execute, in the following format:

　　　　

Minute hour day Month Week command

which

Minute: Represents minutes, which can be any integer from 0 to 59.

Hour: Represents the hour, which can be any integer from 0 to 23.

Day: Represents a date, which can be any integer from 1 to 31.

Month: Represents the month, which can be any integer from 1 to 12.

Week: Represents the day of the week, which can be any integer from 0 to 7, where 0 or 7 represents Sunday.

Command: Commands to execute, either system commands or script files that you write yourself

　　In each of these fields, you can also use the following special characters:

Asterisk (*): represents all possible values, such as the month field if it is an asterisk, the command action is executed monthly after the constraints of other fields are met.

Comma (,): You can specify a list range with a comma-separated value, for example, "1,2,5,7,8,9"

Middle Bar (-): An integer range can be represented by a middle bar between integers, such as "2-6" for "2,3,4,5,6"

Forward slash (/): You can specify the interval frequency of the time with a forward slash, such as "0-23/2", which is performed every two hours. A forward slash can be used with asterisks, such as */10, if used in the minute field, which means that it executes every 10 minutes.

Linux crontab Command Detailed