How to realize the Application scenario and basic use of Crontab in Linux

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Linux version: CentOS 6.6

Application scenarios, such as:

① executes a program every minute to check the running status of the system.

② needs to do statistics on the business data of the past day in the early hours of every morning.

③ needs to back up log files every week.

④ backs up the database every month.

Crontab is a tool for setting periodic execution. The task that is executed periodically is called Cron Job, and the periodic execution list is called Cron Table.

[check crontab service]

① checks if the Crontab tool is installed:

The code is as follows:

Crontab-l

② checks whether the crontab service is started:

The code is as follows:

Service crond status

If the cron service is not installed, you can install the cron service with the following command:

The code is as follows:

Yum install vixie-cron

Yum install crontabs

Example 1. Prints the current time to a log file every minute

The code is as follows:

Corntab-e

Press O and enter:

The code is as follows:

* / 1 * date > > / tmp/log.txt

Press Esc and enter: wq! Save.

Reuse

The code is as follows:

Crontab-l

View scheduled tasks:

View the current time:

The code is as follows:

Date

View / tmp/log.txt

The code is as follows:

Tail-f / tmp/log.txt

Tail-f: keep displaying the last few lines of a file

Tail-3: displays the last three lines of a file

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