Linux System Command Learning Series-timed Task crontab command

Previous section review:

1. Use of the AT command

2. Job: Create a task 10 minutes after shutdown

At now+10 minutes

At>shutdown

At><eot>

In this section we proceed to the second command of the routine task management command: Cron

Before using the command, see if the Crond service is turned on

Service Crond Status

If it is not turned on, it can be opened with service Crond start

Note: Some Linux system service Cron status to view.

1. Editing Task Crontab–e

The format of the crontab command is as follows

* * * * * command

This format is preceded by 5 * followed by a command to execute

The meanings of 5 stars are:

The first *, representing minutes, 1-59, per minute can be expressed in * and */1

The second *, representing the hour, 0-23

The third *, which represents a date, 1-31

Fourth *, indicating the month, 1-12

Fifth *, representing the week, 0-6,0 said Sunday

Here are some examples to illustrate

* * * * * echo ' hello ' >>/tmp/test.txt

*/1 * * * * echo ' hello ' >>/tmp/test.txt

The above indicates that the output of Hello is executed every minute and the output is written to the/tmp/test.txt file

After you save the exit, you can see that the hello is output in the/tmp/test.txt

More examples:

* */1 * * * echo ' hello ' >>/tmp/test.txt

Indicates hourly execution

* 23-3/1 * * * echo ' hello ' >>/tmp/test.txt

Indicates that 23 to 3 points are executed every hour.

* * * echo ' hello ' >>/tmp/test.txt

To be executed 8:30 every night.

1 * * echo ' hello ' >>/tmp/test.txt

Indicates 1th # 10:10 per month to perform operations

1 1 * echo ' hello ' >>/tmp/test.txt

Represents an operation on January 1 10:10 every year

Ten * * 1 echo ' Hello ' >>/tmp/test.txt

Represents every Monday 10:10 operation

2. View Task Crontab–l

Use Crontab–l to see all your custom tasks

The command exists in the/var/spool/cron/root file

3. Delete All Tasks Crontab–r

Use Crontab–r to delete all custom tasks

4. System built-in timer task

Below the/etc/you can see

There are cron.daily,cron.hourly,cron.monthly,cron.weekly folders that represent the daily, hourly, monthly, and weekly scheduled tasks to be performed by the system. Take one of these as an example to see the system's timing tasks

Job: Define a timed task that outputs Hello world to the/tmp/test.txt file every minute

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Linux System Command Learning Series-timed Task crontab command