Crontab Timing Task Detailed

Scheduled tasks are divided into 2 species:

1. Exceptions: Perform the work according to a certain cycle, such as monthly salary, daily work report, daily need of punch, etc.

2. Temporary: Specify the time to execute the order, this time do not have to do next time, such as girlfriend's birthday, leadership inspection work, etc.;

The work of these scheduled tasks Linux can also help us, for example: Every day early 6 : 00 before work email

for recurring tasks, use Cron order;

for temporary tasks, use at order;

at Command: Executes the specified command at a specified time, and then cancels the command from the system after execution;

Cron Command: Executes the specified command periodically at a specified time;

installation crontab :

Yum Install Crontabs

Description

/etc/init.d/crond Start Start the service

/etc/init.d/crond Stop Close Service

/etc/init.d/crond Restart Restart Service

/etc/init.d/crond Reload Reload Configuration

View crontab Service Status: /etc/init.d/crondd Status

View crontab If the service is set to boot, execute the command: Ntsysv

add to boot: chkconfig–level Crond on

1. crontab command

function Description: Setting Timers

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

Additional notes: 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, and 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 Delete the user's timer settings;

-u< User name > Specifies the name of the user to set the timer;

2. crontab format

Basic format: * * * * * command

              points   when   Day   Month   Week     Command

The 1th column represents: Minutes 1~~59 per minute with * or */1

The 2nd column indicates: Hour 1~~23 (0 means 0 points)

The 3rd column represents: Date 1~~31

The 4th column indicates: Month 1~~12

The 5th column represents: Week 0~~6 (0 = Sunday)

The 6th column represents: Run command

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3. Case

* * * * * /etc/init.d/nginx Restart restart Nginx every 21:30

45 4 1 ,10,22 * */etc/init.d/nginx restart       1, 10, 22nd 4:45 minutes restart Nginx

10 1 * * 6 ,0/etc/init.d/nginx restart            1:10 Restart Nginx per week, 6th

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

every 30 minutes

0 * * 6/etc/init.d/nginx restart                Restart Nginx

at 23 points per Saturday

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

every hour

* 23-7/1 * * */etc/init.d/nginx restart            23 o'clock to 7 a.m., restart Nginx

every hour

0 4 * Mon-wed/etc/init.d/nginx restart          Monday to Wednesday 11 o'clock, 4th/month restart Nginx

0 4 1 Jan */etc/init.d/nginx restart 4-point restart of nginx on January 1

*/30 * * * * /usr/sbin/ntpdate 210.72.145.20 synchronize time every 30 minutes

This article is from the "rely on some numbers" blog, please be sure to keep this source http://liubao0312.blog.51cto.com/2213529/1601293

Crontab Timing Task Detailed