Linux Task management

There are two types of task management under Linux, one-time and periodic. One-time is at and batch, and the cycle is divided into system tasks and user tasks.

Disposable tasks:

1. Command format: at [option] Time

2. Option option:-l Specify queue-F to specify file-L view Queue-D Delete queue

3, Time:teatime noon midnight Teatime tomorrow Now

4, the execution method: with at command has the interactive way and the batch processing two kinds of ways. Interactive is when the user enters at [option] time and waits for the user to continue entering the command to execute at the cursor, then submits the task with Ctrl+d. The batch will use-F, the user will execute the command to write to the file, and then use-F to specify the file.

5. Execution result: The result of execution will be sent to the user in the likeness of mail.

6, and Batch difference: Batch can not specify the time, but choose the user system idle time to execute.

Recurring tasks:

Principle of execution: Both the system task and the user task are performed 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, formatted as * * * user command

Time Format: *-. /is a symbol that can be used. * represents all the desirable values for that bit,-represents a continuous value in this interval. Represents the discrete value of this interval,/#表示在某区间每隔 # Perform a task

User tasks:

Command: Using the crontab command, you can use the parameters of the-e call editor in editor to edit,-u Specify the user,-L to view the task,-R to delete the crontab file.

Example:

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

Not divisible how to resolve: available at execution. Write in file while True;do Ls/sleep 10;done

In addition to Crontab, there is also a command to Supplement crontab, Anacron. It is used to detect if a task in Crontab has missed the last time it was executed, and if so, to have the task execute at some time after booting.

　　　　　　　　

Linux Task management