How to use crontab to run scheduled tasks in CentOS Linux

Install crontab: yuminstallcrontabs description: /sbin/servicecrondstart // start the service/sbin/servicecrondstop // close the service/sbin/servicecrondrestart // restart the service/sbin/servicecrondreload // re-load...

 

Install crontab:

Yum install crontabs

 

Note:

/Sbin/service crond start // start the service

/Sbin/service crond stop // close the service

/Sbin/service crond restart // restart the service

/Sbin/service crond reload // reload the configuration

 

 

View crontab service status: service crond status

 

Start the crontab service manually: service crond start

 

Check whether the crontab service is set to start at startup. run the following command: ntsysv.

 

Add boot auto start:

Chkconfig-level 35 crond on

 

1. crontab command

 

Function description: sets a timer.

 

Syntax: crontab [-u <用户名称> ] [Configuration file] or crontab [-u <用户名称> ] [-Elr]

 

Note: cron is a resident service that provides the timer function to allow users to execute preset commands or programs at specific times. You can use the timer function as long as you edit the timer configuration file. The configuration file format is as follows:

Minute Hour Day Month DayOFWeek Command

 

Parameters:

-E: Edit the timer settings of the user.

-L list the timer settings of this user.

-R: delete the timer settings of this user.

-U <用户名称> Specifies the user name to set the timer.

 

2. crontab format

 

Basic format:

* *** Command

Hour, day, month, and Week commands

 

The 1st column indicates minute 1 ~ 59. each minute is represented by * or */1.

The first column indicates the hour 1 ~ 23 (0 indicates 0 points)

The 3rd column indicates the date 1 ~ 31

The 4th column indicates the month 1 ~ 12

The identification number of column 5th is from day of the week to day ~ 6 (0 indicates Sunday)

6th columns of commands to run

 

# Use the hash sign to prefix a comment

# + ------ Minute (0-59)

# | + ----- Hour (0-23)

# | + ---- Day of month (1-31)

# | + --- Month (1-12)

# | + -- Day of week (0-7) (Sunday = 0 or 7)

# |

# ***** Command to be executed

 

Some examples of crontab files:

 

30 21 ***/etc/init. d/nginx restart

Restart nginx at every night.

 

45 4, 10, 22 **/etc/init. d/nginx restart

Restart nginx at on the 1st, 10th, and 22th of every month.

 

10 1 ** 6, 0/etc/init. d/nginx restart

Restart nginx at every Saturday and Sunday.

 

0, 30 18-23 ***/etc/init. d/nginx restart

Restart nginx every 30 minutes from to every day.

 

0 23 ** 6/etc/init. d/nginx restart

Restart nginx at every Saturday.

 

**/1 ***/etc/init. d/nginx restart

Restart nginx every hour

 

* 23-7/1 ***/etc/init. d/nginx restart

Restart nginx every hour between PM and PM.

 

0 11 4 * mon-wed/etc/init. d/nginx restart

Restart nginx from every Monday to every Wednesday on the 4th of each month

 

0 4 1 jan */etc/init. d/nginx restart

Restart nginx at on January 1, January 1

 

*/30 */usr/sbin/ntpdate 210.72.145.20

Synchronization time every half hour

 

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