LinuxVPS/use Crontab on the server to automate VPS

LinuxVPS/use Crontab on the server to automate VPS

VPS or servers often require VPS or servers to regularly back up data, regularly restart a service, or regularly execute a program. Generally, Crontab is used in Linux, in Windows, scheduled tasks are used (Windows's Gui settings are relatively simple). The following describes how to install and use Crontab on Linux VPS/server.

Crontab is a common scheduled execution tool in Unix/Linux systems. It can run specified jobs without manual intervention.

1. Installing Crontab 1. Installing Crontab under CentOS

Yum install vixie-cron crontabs // install Crontab

Chkconfig crond on // set to auto-start upon startup
Service crond start // start

Note: The vixie-cron software package is the main program of cron. The crontabs software package is used to install, uninstall, or list the tables used to drive the cron daemon process.

2. Install Crontab under Debian

Apt-get install cron // Debian is installed in most cases.

/Etc/init. d/cron restart // restart Crontab

Ii. How to Use Crontab 1. View crontab scheduled execution task list crontab-l2 and add crontab scheduled execution task crontab-e

When you enter the crontab Task Command, the default editor of crontab may be different.

As shown in, the nano editor is easy to use. Simply press the crontab command format at the end of the file, press Ctrl + x to exit, and press y to save.

In the vi Editor, press the I key, press the crontab command format at the end of the file, press the ESC key, and press ENTER wq to press the Enter key.

3. crontab Task Command writing format

Format:	Minute	Hour	Dayofmonth	Month	Dayofweek	Command
Explanation:	Minutes	Hours	Date	Monthly payment	Week	Command
Range:	0-59	0 ~ 23	1 ~ 31	1 ~ 12	0 ~ Both 7, 0, and 7 represent Sunday.

In crontab, we often use the four symbols "*" and "-/n". Well, I 'd like to draw another table to make it clearer:

Symbol	Explanation
* (Asterisk)	All valid values. For example, the backup command is executed at, regardless of the number of months, days, and weeks.
, (Comma)	Split multiple values. For example, execute the command at 09:30 on the first, 16th, and 20th of every month.
-(Minus sign)	Represents a period of time. For example, 0 9-17 *** checkmail executes the checkmail command from to every day.
/N	It indicates a long interval of n. For example, */5 * check executes the check command every 5 minutes, which is the same as 0-59/5.

The following are some examples for better understanding:

Run the backup program at every day: 0 3 ***/root/backup. sh

Run the log cleanup program at 08:30 every Sunday: 30 8 ** 7/root/clear. sh

Run the test program at 5 zero o'clock every week: 0 0 ** test

Run the wenchuan program at on January 1, May 12 every year: 0 14 12 5 */root/wenchuan

Restart php-fpm from to every 15 minutes: */15 18-23 ***/etc/init. d/php-fpm