CentOS installation crontab and how to use it

Install Crontab:
[email protected] ~]# Yum install Vixie-cron
[email protected] ~]# Yum install Crontabs

Description
Vixie-cron package is the main program of Cron;
The Crontabs package is a program used to install, uninstall, or list tables used to drive the cron daemon.
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Cron is a built-in service for Linux, but it does not automatically get up, and you can start and shut down this service in the following ways:
/sbin/service Crond Start//Startup service
/sbin/service Crond stop//Shut down service
/sbin/service crond Restart//Restart service
/sbin/service Crond Reload//Reload Configuration

View crontab Service Status: Crond status

Manually Start crontab services: Service Crond start

To see if the Crontab service is set to boot, execute command: NTSYSV

Add to boot auto start:
Chkconfig--level Crond on

1,crontab command

Feature Description: Set the timer.

Syntax: crontab [-u < user name >][profile] or crontab [-u < user name >][-ELR]

Additional note: Cron is a resident service that provides the function of a timer that allows the user to execute a preset instruction or program at a specific time. The function of the timer can be used as long as the user edits the timer's configuration file. Its configuration file format is as follows:
Minute Hour Day Month DayOFWeek Command

Parameters
-e Edit the user's timer settings.
-l lists the user's timer settings.
-R removes the user's timer settings.
-u< User name > Specifies the user name to set the timer.

2,crontab format

Basic format:
* * * * * command
Time-sharing Weekly command

The 1th column represents minutes 1~59 per minute with * or */1
The 2nd column represents the hour 1~23 (0 means 0 points)
The 3rd column represents the date 1~31
The 4th column represents the month 1~12
5th Column Identification Number Week 0~6 (0 = Sunday)
6th List of commands to run

Some examples of crontab files:

* * * * */usr/local/etc/rc.d/lighttpd restart
The above example shows that 21:30 restarts Apache per night.

4 1,10,22 * */USR/LOCAL/ETC/RC.D/LIGHTTPD restart
The above example shows that 4:45 restarts Apache on the 1, 10, and 22nd of the month.

1 * * 6,0/USR/LOCAL/ETC/RC.D/LIGHTTPD restart
The above example shows that 1:10 restarts Apache every Saturday and Sunday.

0,30 18-23 * * */usr/local/etc/rc.d/lighttpd restart
The above example shows that Apache restarts every 30 minutes from 18:00 to 23:00 every day.

0 * * 6/USR/LOCAL/ETC/RC.D/LIGHTTPD restart
The above example shows the restart of Apache every Saturday at 11:00am.

* */1 * * * */usr/local/etc/rc.d/lighttpd restart
Restart Apache every hour

* 23-7/1 * * * */usr/local/etc/rc.d/lighttpd restart
From 11 o'clock to 7 in the morning, restart Apache every hour.

0 4 * mon-wed/usr/local/etc/rc.d/lighttpd restart
4th per month with 11-point restart from Monday to Wednesday Apache

0 4 1 Jan */usr/local/etc/rc.d/lighttpd restart
4-point restart of Apache on January 1

*/30 * * * */usr/sbin/ntpdate 210.72.145.44
Synchronize time every half hour

The CRONTAB command has 3 main parameters:

-E: Edit the user's crontab.

-L: Lists the contents of the user's crontab.

-r: Deletes the contents of the user's crontab.

Execute CRONTAB-E, will automatically open the editor, you can edit your own crontab files, syntax and/etc/crontab files, different just, do not have to point out the execution of the user, edit and save.

Crontab-l used to view their crontab files, crontab-r delete their crontab.

CentOS installation crontab and how to use it