Use Cron to set timed tasks under CentOS and Ubuntu

1. Start the Cron tool [PS: Use root privileges]

CentOS Boot cron Two ways

A)/etc/init.d/crond start

b) Service Crond start

Ubuntu Startup Cron Two ways

A)/etc/init.d/cron start

b) Service cron start (recommended)

2. Add timed tasks [execute LS command per hour]

Centos

CRONTAB-E command to open a file

Add a line: 0 * * * * ls

Ubuntu

CRONTAB-E command to open the file [PS: The first time with this command, will let you select a text editor, enter the corresponding editor number, the question is explained later]

Add a line: 0 * * * * ls

Save exit

3. View Scheduled Tasks

centos| | Ubuntu

Crontab-l

Above is the operation of a simple scheduled task,

crontab command Options

crontab file [-u user] replaces the default crontab file with the specified files, for example: Crontab/var/mycron.txt-u root

If you want to restore the default file, perform a crontab-r delete task

crontab-l [-u user] lists the current tasks for the specified user

CRONTAB-E [-u user] Edit specified user timing task

Crontab-r [-u user] Deletes the current task for the specified user

crontab file Syntax

The format is: minutes (0-59) hours (0-23) days (1-31) months (1-12) weeks (0-6) Order (command)

Remember the meanings of several special symbols:

"*" represents a number in the range of values,

"/" stands for "every",

"-" represents a number to a number,

"," separate a few discrete numbers

For example:

5 * * * * ls indicates the first 5 minutes of each hour to execute the LS command

5 * * 0 ls indicates the LS command is executed at 5:30 points per Sunday

3-8 * * ls indicates that the LS command is executed at the 20th point every day from 3 o'clock to 8.

*/15 * * * * * php-f/varwww/index.php means the php file is executed once per hour 0,15,30,45

　　　　

　　

Let's talk about some of the difficulties I've encountered in Ubuntu.

I forgot to choose the editor when I was crontab-e, so I came up with this interface

This is forgetting to choose Vim Editor, in fact can also be edited in the file, just a little strange, OK, continue

After adding the execution task to the last line of the file: Ctrl+x exit, then enter Y to save, then return to exit, OK, it's done.

But I'm a compulsive patient, feeling a little uncomfortable, I want to use VIM, continue

Enter sudo select-editor on the command line, select the corresponding vim serial number, OK, finally complete

Use Cron to set timed tasks under CentOS and Ubuntu