Linux operating system timing task system

cron is a timed execution tool for Linux that runs jobs without human intervention. Since Cron is a built-in service for Linux, but it does not automatically get up, you can start and shut down the service in the following ways:

/sbin/service crond start //Start the service

/sbin/Service crond stop //close service

/sbin/service crond restart //restart service

/sbin/service crond reload //reload configuration

You can also This service is automatically started when the system is started:

At the end of the /etc /rc.d/rc.local script:

/sbin/service crond start

Now that the Cron service is already in the process, we can use this service. The Cron service provides the following interfaces for everyone to use:

1. Edit directly with the crontab command

The cron service provides the crontab command to set the cron service. The following are some parameters and descriptions of this command:

crontab -u //Set a user's cron service, generally the root user is executing this This parameter is required when the command is

crontab -l //list some use The details of the cron service

crontab -r //delete the cron service without a user

crontab -e //edit a user's cron service

For example, root Check your own cron settings: crontab -u root -l

For example, root wants to delete fred's cron settings: crontab -u fred -r

When editing the cron service, edit the content There are some formats and conventions, enter: crontab -u root -e

Enter the vi edit mode, the edited content must conform to the following format: */1 * * * * ls >> /tmp/Ls.tx t

crond resident command for task scheduling

crond is a command that linux uses to execute programs on a regular basis. This task scheduling command is initiated by default when the operating system is installed. The crond command periodically checks for work to be performed every minute, and if there is work to be performed, it will be automatically executed.

1. The task of linux task scheduling is mainly divided into the following two categories:

*The work performed by the system: the work to be performed periodically by the system, such as backing up system data, cleaning the cache

*Personal Execution: A job that a user does on a regular basis, such as checking the mail server for new messages every 10 minutes, which can be set by each user.

2.crontab command options:

-u specifies a user,

-l lists a user's task plan,

-r delete A user's task,

-eEdit a user's task

3.cron file syntax:

minute hour, month, and week week command

0-59 0-23 1-31 1-12 0-6 command (value range, 0 means that a general line corresponds to a task on Sunday)

4. Remember the meaning of several special symbols:

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

"/" stands for " every ",

"-" represents from some Number to a number,

"," separate several discrete numbers

First, the task scheduling setting file is written

can be edited with crontab -e command Edit the user's cron file under /var/spool/cron, or modify the /etc/crontab file directly

The specific format is as follows:

Minute Hour Day Month Dayofweek command

Minutes, hours, days, days, and weeks Order

Each field represents the following meaning:

Minute Performs the task every few minutes of the hour

Hour performs the task for the first few hours of the day
>

Day Perform the task on the first few days of the month

Month Perform the task in the first few months of each year

DayOfWeek Perform the task on the first few days of each week

Command Specifies the program to be executed

In these fields, except for the fields that must be specified each time, the other fields are optional fields, which can be determined as needed. For fields that are not specified, use “*” to fill their location.

Examples are as follows:

5 * * * * ls Specifies the ls command to be executed once every 5 minutes of the hour

30 5 * * * ls specifies 5:30 every day Execute the ls command

30 7 8 * * ls Specify 7:30 on the 8th of each month to execute the ls command

30 5 8 6 * ls Specify 5:30 on June 8th of each year Execute the ls command

30 6 * * 0 ls Specify to execute the ls command every 6:30 on Sunday [Note: 0 means Sunday, 1 means week 1, and so on, it can also be expressed in English, sun means On Sunday, mon said Monday and so on. ]

30 3 10,20 * * ls Execute the ls command at 3:30 on the 10th and 20th of each month [Note: “, & rdquo; used to connect multiple non-contiguous time slots]

25 8-11 * * * ls Execute the ls command at the 25th minute of 8-11 every day [Note: “-” used to connect consecutive time periods]

*/15 * * * * ls Execute the ls command every 15 minutes [ie 0 15 30 45 per hour 60 minutes to execute the ls command]

30 6 */10 * * ls Every 10 days, every 10 days : 30 Execute an ls command [that is, execute the ls command at 6:30 on the 1, 11, 21, and 31 of each month. ]

Execute all executables in the /etc/cron.daily directory as root at 7:50 every day

50 7 * * * root run-parts /etc/cron.daily [ ,null,null,3],Note: The run-parts parameter indicates that all executable files in the following directory are executed. ]

Second, the new scheduling task

There are two ways to add a new scheduling task:

1. At the command line, type: crontab -e and add the corresponding task. Wq saves and exits.

2, directly edit the /etc/crontab file, vi /etc/crontab, add the corresponding task.

Third, view the scheduling task

crontab -l //list all current scheduling tasks

crontab -l -u jp //list all scheduling of user jp Task

Fourth, delete the task scheduling work

crontab -r //delete all task scheduling work

Five, the task scheduling execution results of the steering

1: Execute the ls command at 5:30 every day and output the result to the /jp/test file

30 5 * * * ls >/jp/test 2>&1

Note: 2>&1 indicates the execution result and error message.

Edit /etc/crontab file configuration cron

The cron service not only reads all the files in /var/spool/cron every minute, but also needs to read /etc/crontab once, so we Configuring this file can also do something with the cron service. The configuration with crontab is for a certain user, and editing /etc/crontab is a task for the system. The file format of this file is:

SHELL=/bin/bash

PATH=/sbin:/bin:/usr/sbin:/usr/bin

MAILTO= Root //If there is an error, or there is data output, the data is sent to this account as an email

HOME=///The path the user runs, here is the root directory

# run-parts

01 * * * * root run-parts /etc/cron.hourly //execute scripts in /etc/cron.hourly every hour

02 4 * * * root run-parts /etc/cron.daily //Execute scripts in /etc/cron.daily every day

22 4 * * 0 root run-parts /etc/cron.weekly //execute /etc/cron every week. Scripts in weekly

42 4 1 * * root run-parts /etc/cron.monthly //execute the scripts in /etc/cron.monthly every month

Note to everyone" Run-parts" This parameter, if you remove this parameter, you can write a script name to run later, instead of the folder name.

For example: 1. At the command line, type: crontab -e Then add the corresponding task, wq save and exit.

2, directly edit the /etc/crontab file, ie vi /etc/crontab, add the corresponding task

11 2 21 10 * rm -rf /mnt/fb