Linux Task Scheduler, recurring task execution

Perform one task at a time in the future: at, Batch

To run a task periodically: cron

e-Mail Service:

Smtp:simple Mail Transmission protocol for mail delivery

Pop3:post Office Protocol

Imap4:internet Mail Access Protocol

Mailx-send and receive Internet mail

Mua:mail User Agent

MAILX [-S ' SUBJECT '] username[@hostname]

The message body is generated:

(1) give directly, Ctrl+d;

(2) Input redirection

(3) through the pipeline

Echo-e "How is you?\nhow old is you?" | Mail

AT command:

At [option] Time

Time:

hh:mm [YYYY-MM-DD]

Noon, midnight, teatime

Tomorrow

Now+#{minutes,hours,days, or weeks}

Common options:

-Q QUEUE:

-L: Lists jobs waiting to be run in the specified queue; equivalent to ATQ

-D: Deletes the specified job; equivalent to ATRM

-C: View specific job Tasks

-f/path/from/somefile: Reading a task from a specified file

Note: The execution result of the job is notified to the relevant user by mail

Batch command:

Allow the system to choose its own idle time to perform the tasks specified here

Recurring Task Scheduler: Cron

Related packages:

Cronie: Main package, provides Crond daemon and related auxiliary tools

Cronie-anacron:cronie to monitor the execution of Cronie tasks, such as when a task in Cronie has not run correctly at a point in time in the past, Anacron will then initiate this task

Crontabs: Includes centos to provide system maintenance tasks

Make sure that the Crond daemon is in a running state:

CentOS 7:

Systemctl Status Crond

CentOS 6:

Service Crond Status

The tasks that are scheduled to be performed periodically are submitted to Crond, which is implemented to the point of operation.

System Cron Task: System maintenance Job,/etc/crontab

User Cron task: crontab command

System Cron Task

# Example of Job definition:

#.----------------Minute (0-59)

# | .-------------Hour (0-23)

# |  | .----------Day of Month (1-31)

# |  |  | .-------month (1-12) OR jan,feb,mar,apr ...

# |  |  |  | .----Day of Week (0-6) (sunday=0 or 7) or Sun,mon,tue,wed,thu,fri,sat

# |  |  |  | |

# * * * * * * user-name command to be executed

Example: Run the echo command at 9:10

* * * * gentoo/bin/echo "howdy!"

Time notation:

(1) A specific value: A value in the range of valid values for a given point in time

(2) *: All values in the range of valid values at a given point in time, indicating "every ..."

(3) Discrete value: #,#,#

(4) Continuous value:-,#-#

(5) in the specified time range, define the step length,/#: #即为步长

Example: Echo command every 3 hours

0 */3 * * * gentoo/bin/echo "howdy!"

User cron:

crontab command definition, each user has a dedicated cron task file:/var/spool/cron/username

crontab command:

crontab [-u user] [-l |-r |-e] [-I.]

-L: List All Tasks

-E: Editing tasks

-R: Remove All Tasks

-I: Use with-R to allow users to selectively remove specified tasks in interactive mode

-U User: Only root can run, manage cron tasks for designated users

Note: The result of the operation is notified to the relevant user by email

(1) COMMAND >/dev/null

(2) COMMAND &>/dev/null

Note: For cron tasks,% has a special purpose; If you want to use% in the command, you need to escape, but if you put% in single quotes, you can also not escape

This article is from the "Ricky Technology Blog" blog, make sure to keep this source http://r1cky.blog.51cto.com/10646564/1773863

Linux Task Scheduler, recurring task execution