How do I set up a scheduled task in Linux using cron?

Linux timing tasks include: cron, anacron, at, etc., and the cron service is mainly introduced here.

Explanation of terms: cron is the service name, crond is the background process, and crontab is the customized scheduled task table.

Package Installation:

To use the cron service, you need to install the vixie-cron package and the crontabs package, which are used as follows:

The vixie-cron package is the main program for cron.

The crontabs package is a program used to install, uninstall, or list the ** used to drive the cron daemon.

Check if the cron package is installed: rpm -qa|grep vixie-cron

Check whether the crontabs package is installed: rpm -qa|grep crontabs

If not, run the following command to install the software package (the package must exist):

rpm -ivh

rpm -ivh crontabs*

yum install vixie-cron

yum install crontabs

The details are as follows: a cron expression is a string, the string is separated by 5 or 6 spaces, divided into 6 or 7 fields, each field represents a meaning, cron has the following two syntax forms: (1) seconds minutes hours dayofmonth month dayofweek year (2) seconds minutes hours dayofmonth month dayofweek

1) Seconds, minutes, days, months, weeks, years.

2) Seconds, minutes, days, months, weeks.

1.seconds Allowed value range: 0 59, not allowed to be empty shed value.

2.Cent Allowed value range: 0 59, null value is not allowed.

3.When the allowed values range: 0 23, null values are not allowed.

4.Day allowed value range: 1-31, null value is not allowed.

5.Month Allowed value range: 1 12 (jan-dec), null values are not allowed.

6.Week Jujube Allowed value range: 1 7 (sun-sat), 1 for Sunday (the first day of the week), and so on, 7 for Saturday (the last day of the week), not allowed to be null.

7.Year Allowed Value Range: 1970 2099 , Allowed to be empty.