Two scheduled task execution methods in linux

Article Title: Two scheduled task execution methods in linux. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

(1) at command

If we want to run a specific task only once, we need to use the at monitoring program.

Setting the at command is very easy. It indicates the time at which the command will be run. At is similar to the print process. It puts the task in the/var/spool/at directory and runs it at the specified time. The at command is equivalent to another shell. when running the at time command, it sends commands one by one and can input any command or program. The at now + time command can be used to indicate the task.

Assume that a large database needs to be processed without a system, for example, at 03:10 AM. Then we should first establish the/home/kyle/do_job script management database and plan to process the results in the/home/kyle/do_job file. The normal method is to start the following command:

# At 2: 05 tomorrow

At>/home/kyle/do_job

At> Ctrl + D

Time Representation in AT Time

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Time example

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Minute at now + 5 minutes task run in 5 minutes

Hour at now + 1 hour task run in 1 Hour

Days at now + 3 days task run in 3 Days

Weeks at now + 2 weeks task run in two Weeks

Fixed at midnight task runs at midnight

Fixed at pm

Note: Check whether the atq service is enabled. Some operating systems may not be started by default. linux does not start by default, whereas ubuntu does. Run the service atd check syntax, run the service atd status Command to check the atd status, and run the service atd start command to start the atd service.

View the specific content of at execution: It is generally located under the/var/spool/at directory and opened with vi. The last part is your execution program.

(2) crontab

Cron is a linux scheduled execution tool that can run jobs without human intervention. Since Cron is a built-in service in Linux, but it does not automatically get up, you can use the following methods to start and close this service:

/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

/Sbin/service crond status // view service status

You can also enable this service automatically when the system starts:

Add:

/Sbin/service crond start

Now that the Cron Service is in the process, we can use it. The Cron Service provides the following interfaces for you to use:

1. directly use crontab for editing

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 needs this parameter when executing this command.

Crontab-l // list the details of a user's cron Service

Crontab-r // delete a user's cron Service

Crontab-e // edit a user's cron Service

For example, to view your cron settings as root: crontab-u root-l

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

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

Some examples of crontab files:

# Restart apache at every night.

30 21 ***/usr/local/etc/rc. d/lighttpd restart

#1, 10, and 22 every month

45 4, 10, 22 **/usr/local/etc/rc. d/lighttpd restart

#06:10 every morning

10 6 **** date

# Every two hours

0 */2 * date

# Every two hours from PM to am, am

0 23-7/2, 8 **** date

# Am on the 4th day of each month and from Monday to Wednesday of each week

0 11 4 * mon-wed date

# A.m. of July

0 4 1 jan * date