Linux Scheduled Tasks

Scheduled Tasks in Linux

Executes the specified task within the agreed time, called a scheduled task.

There are generally two ways to schedule tasks in Linux:

Scheduled Tasks and recurring scheduled tasks that are performed at once

One-time scheduled tasks, using command at

a at: Perform a specified task at a specified time in the future ;

It is used in the format: at [option] ... Time

Time is specified.

(1) Absolute time

hh:mm

Mmdd[cc]yy,

Mm/dd/[cc]yy,

Dd.mm.[cc]yy or [Cc]yy-mm-dd

Example 1:650) this.width=650; "Src=" http://s3.51cto.com/wyfs02/M02/72/DD/wKioL1Xu_UmQQJMgAABzEoaNwVI956.jpg " Title= "At1.png" alt= "Wkiol1xu_umqqjmgaabzeoanwvi956.jpg"/>

Submit the task using Ctrl+d after the input is complete

(2) Relative time

now+ #UNIT The #unit time after the current time

Unit: Minute, hour, day, week

Example 2:650) this.width=650; "Src=" http://s3.51cto.com/wyfs02/M00/72/DD/wKioL1Xu_fyxZES9AAB4imlfbMc427.jpg " Title= "At2.png" alt= "Wkiol1xu_fyxzes9aab4imlfbmc427.jpg"/>

(3) Blur time

Midnight,noon,teatime,tomorrow,minute, hour, day, week

[option] Options for command execution

Common options:

-L: View a list of such running jobs in the job queue; equivalent to using the ATQ command;

-C At_job_num: Look at the contents of the running job, At_job_num is the job ID number;

-Q queue:at Job queue;

-D: Delete the specified job; equivalent to ATRM

Example 3:650) this.width=650; "Src=" http://s3.51cto.com/wyfs02/M01/72/DD/wKioL1XvACjxqua6AAEyEX8Yoqc561.jpg " Title= "At3.png" alt= "Wkiol1xvacjxqua6aaeyex8yoqc561.jpg"/>

-f/path/from/somefile: Reads the job to be run from the specified file;

Two recurring tasks

There are two types of recurring tasks:

(1) System cron task; There is no default running user identity, so you need to specify the additional runner;

Task File/etc/crontab program is edited by default using Vim

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

First 5 fields: Time points, respectively, day and week

After 2 fields:

User-name: Run the task as a user

command to being executed: to run a task

(2) User Cron Task: Submitted by a user, the default is to run as the submitter, so there is no need to specify additional

run by;

/var/spool/cron/username

# * * * * * command to be executed

5 Time points:

Minutes: valid value range 0-59;

Hours: 0-23

Day: 1-31

Month: 1-12

Weeks: 0-7

Note: The date of the month and the number of weeks, not recommended to use at the same time;

Time notation:

*: Each time point in the valid value range of the time point;

-: A specific continuous time range, 3-7

,: A discrete point in time, 3,5,7

/#: The amount of time in a valid time frame, for specifying the frequency;

(3) Example/bin/echo * * * * * * "Hello world!"

Represents 15:30 of daily tasks

Example * * * * 4/bin/echo "Hello world!"

Represents 15:30 per Thursday of performing tasks

Example 1-4 * */bin/echo "Hello world!"

Represents 15:30 missions per Monday through Thursday

Example 3,7 * */bin/echo "Hello world!"

Represents the 15:30 missions of 3rd and 7th each month.

Example 5:*/6 * * * */bin/echo "Hello world!"

Indicates that a scheduled task is executed every 6 minutes

Example 6:1 */4 * * */bin/echo "Hello world!"

Indicates that a scheduled task is performed every 4 hours, and if the minute field is *, it is reached

Every minute of the hour is executed.

(4) crontab command:

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

-u User: Not managing your own cron task, but specifying the target user's cron task; root only

Manage the permissions of other users ' cron tasks, and manage their own by default;

-l:list, list the tasks;

-r:remove to remove all tasks;

-e:edit, edit, open a default editor for the current shell session to edit the cron task table;

Homework Exercises:

1, every Monday to Saturday 3:20 A.M., run the CP command to archive the/etc/directory, storage location is/BACKUPS/ETC-YYYY-MM-DD;

2 0 3 * * 1-6/usr/bin/cp-r/etc//backups/etc-$ (date + '%y-%m-%d ')

2, every Sunday 2:30 A.M., run the CP command to backup the/etc/fstab file, the storage location is/BACKUP/FSTAB-YYYY-MM-DD-HH-MM-SS;

3 0 2 * * 0/usr/bin/cp/etc/fstab/backups/etc-$ (date + '%y-%m-%d-%h-%m-%s ')

3, every night 12 o'clock, get all the lines in the/proc/meminfo file starting with S or M, appended to the/statistics/meminfo.txt file, and the daily message before, to add a similar =============== separator line;

0 0 * * * echo "==============================================" >> meminfo.txt &&/usr/bin/egrep "^ (s| M) "/proc/meminfo >> meminfo.txt

Linux Scheduled Tasks