Shell learns 57 days----Linux task management, summarizing and extending to the previous lecture

Linux task Management

There are two types of task management under Linux , each of which is one-time and periodic . Disposable is at and the Batch, periodicity is divided into the system regardless of what and user tasks .

Disposable Tasks :

1. Command format : at [ options ] time

2. Options :

Option name	Description
-I ( uppercase I)	Specify a queue
-F	Specify file
-L ( lowercase l)	View queues
-D	Delete queue

3.time:teatime noon Midnight Teatime tomorrow Now

4, operation mode: With at command has interactive mode and batch processing two ways.

Interactive is when the user enters at [option] time and waits for the user to continue entering the command to run at the cursor, and then submits the task with ctrl+d . The batch is going to use -F. is the command that the user will run to write to the file, and then use - f to specify the file.

5. Running result: The result of the operation will be sent to the user in the likeness of the mail.

6, and batch difference:Batch can not specify the time, but choose the user system spare time to run.

Recurring tasks:

How it works: Both the system task and the user task are run by the daemon crond reading the user-defined file. When the system task file is /etc/crontab, the user task file is /var/spool/cron/username.

System tasks:

Task definition Format: Each row defines a task. Format is * * * user command

Time Format:*-./ is a symbol that can be used. * represents all the desirable values for this bit. - represents a continuous value in this interval. . represents the discrete value of this interval, /# indicates that at intervals of # run a task once

User tasks:

Command: Use the crontab command. The number of parameters that can be used is the- e call editor in editor to edit,-u Specify user,-l View tasks,-r Delete crontab files.

Examples:

How to achieve a second-level task:* * * * * * for i in {1...4};d o/bin/echo "Hello"; Sleep 1;done

Not divisible how to solve: available at run. Write in the file while true;do ls/sleep 10;done

In addition to the crontab , another command is a supplement to crontab ,anacron.

It is used to detect If a task in the crontab has missed the last run time, and if so, let the task run at some time after power-on.

Shell learns 57 days----Linux task management, summarizing and extending to the previous lecture